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Code Editor : socat.html

<html><head>
<title>socat</title>
<link rev="made" href="mailto:socat@dest-unreach.org">
</head>
<body>
<hr>
<h1>socat</h1>
<h2> </h2>

<a name="CONTENTS"></a>
<h2>CONTENTS</h2>
<a href="socat.html#NAME">NAME</a> 
<a href="socat.html#SYNOPSIS">SYNOPSIS</a> 
<a href="socat.html#DESCRIPTION">DESCRIPTION</a> 
<a href="socat.html#OPTIONS">OPTIONS</a> 
<a href="socat.html#ADDRESS_SPECIFICATIONS">ADDRESS SPECIFICATIONS</a> 
<a href="socat.html#ADDRESS_TYPES">ADDRESS TYPES</a> 
<a href="socat.html#ADDRESS_OPTIONS">ADDRESS OPTIONS</a> 
<a href="socat.html#VALUES">DATA VALUES</a> 
<a href="socat.html#EXAMPLES">EXAMPLES</a> 
<a href="socat.html#DIAGNOSTICS">DIAGNOSTICS</a> 
<a href="socat.html#FILES">FILES</a> 
<a href="socat.html#ENVIRONMENT_VARIABLES">ENVIRONMENT VARIABLES</a> 
<a href="socat.html#CREDITS">CREDITS</a> 
<a href="socat.html#VERSION">VERSION</a> 
<a href="socat.html#BUGS">BUGS</a> 
<a href="socat.html#SEEALSO">SEE ALSO</a> 

<a name="NAME"></a>
<h2>NAME</h2>socat - Multipurpose relay (SOcket CAT)

<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
<code>socat [options] &lt;address&gt; &lt;address&gt;</code> 
<code>socat -V</code> 
<code>socat -h[h[h]] | -?[?[?]]</code> 
<code>filan</code> 
<code>procan</code>

<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>

Socat is a command line based utility that establishes two bidirectional byte
streams and transfers data between them. Because the streams can be constructed
from a large set of different types of data sinks and sources 
(see <a href="socat.html#ADDRESS_TYPES">address types</a>), and because lots of
<a href="socat.html#ADDRESS_OPTIONS">address options</a> may be applied to the streams, socat can
be used for many different purposes. 

Filan is a utility that prints information about its active file
descriptors to stdout. It has been written for debugging socat, but might be
useful for other purposes too. Use the -h option to find more infos.

Procan is a utility that prints information about process parameters to
stdout. It has been written to better understand 
some UNIX process properties and for debugging socat, but might be 
useful for other purposes too.

The life cycle of a socat instance typically consists of four phases.

In the init phase, the command line options are parsed and logging is
initialized. 

During the open phase, socat opens the first address and afterwards the
second address. These steps are usually blocking; thus, especially for complex address types like socks,
connection requests or authentication dialogs must be completed before the next
step is started.

In the transfer phase, socat watches both streams' read and write file
descriptors via 
<code>select()</code>
, and, when data is available on one side and
can be written to the other side, socat reads it, performs newline
character conversions if required, and writes the data to the write file
descriptor of the other stream, then continues waiting for more data in both
directions.

When one of the streams effectively reaches EOF, the closing phase
begins. Socat transfers the EOF condition to the other stream,
i.e. tries to shutdown only its write stream, giving it a chance to
terminate gracefully. For a defined time socat continues to transfer data in
the other direction, but then closes all remaining channels and terminates.

<a name="OPTIONS"></a>
<h2>OPTIONS</h2>

Socat provides some command line options that modify the behaviour of the
program. They have nothing to do with so called
<a href="socat.html#ADDRESS_OPTIONS">address options</a> that are used as parts of <a href="socat.html#ADDRESS_SPECIFICATIONS">address specifications</a>.

<dl>
<dt><code>-V</code><dd>
 Print version and available feature information to stdout, and exit.
<dt><code>-h | -?</code><dd>
 Print a help text to stdout describing command line options and available address
 types, and exit.
<dt><code>-hh | -??</code><dd>
 Like -h, plus a list of the short names of all available address options. Some options are
 platform dependend, so this output is helpful for checking the particular
 implementation. 
<dt><code>-hhh | -???</code><dd>
 Like -hh, plus a list of all available address option names.
<a name="option_d"></a><dt><code>-d</code><dd>
 Without this option, only fatal and error messages are generated; applying
 this option also prints warning messages. See <a href="socat.html#DIAGNOSTICS">DIAGNOSTICS</a>
 for more information. 
<a name="option_d_d"></a><dt><code>-d -d</code><dd> Prints fatal, error, warning, and notice messages.
<dt><code>-d -d -d</code><dd> Prints fatal, error, warning, notice, and info messages.
<dt><code>-d -d -d -d</code><dd> Prints fatal, error, warning, notice, info, and debug
 messages. 
<dt><code>-D</code><dd>
 Logs information about file descriptors before starting the transfer phase.
<dt><code>-ly[&lt;facility&gt;]</code><dd>
 Writes messages to syslog instead of stderr; severity as defined with -d
 option. With optional <a href="socat.html#TYPE_FACILITY">&lt;facility&gt;</a>, the syslog type can
 be selected, default is "daemon". Third party libraries might not obey this
 option.
<dt><code>-lf</code><code> &lt;logfile&gt;</code><dd>
 Writes messages to &lt;logfile&gt; [<a href="socat.html#TYPE_FILENAME">filename</a>] instead of
 stderr. Some third party libraries, in particular libwrap, might not obey
 this option.
<dt><code>-ls</code><dd>
 Writes messages to stderr (this is the default). Some third party libraries 
 might not obey this option, in particular libwrap appears to only log to
 syslog. 
<a name="option_lp"></a><dt><code>-lp</code><code>&lt;progname&gt;</code><dd>
 Overrides the program name printed in error messages and used for
 constructing environment variable names.
<dt><code>-lu</code><dd>
 Extends the timestamp of error messages to microsecond resolution. Does not
 work when logging to syslog.
<a name="option_lm"></a><dt><code>-lm[&lt;facility&gt;]</code><dd>
 Mixed log mode. During startup messages are printed to stderr; when socat 
 starts the transfer phase loop or daemon mode (i.e. after opening all
 streams and before starting data transfer, or, with listening sockets with
 fork option, before the first accept call), it switches logging to syslog. 
 With optional <a href="socat.html#TYPE_FACILITY">&lt;facility&gt;</a>, the syslog type can be
 selected, default is "daemon". 
<a name="option_lh"></a><dt><code>-lh</code><dd>
 Adds hostname to log messages. Uses the value from environment variable
 HOSTNAME or the value retrieved with <code>uname()</code> if HOSTNAME is not set.
<dt><code>-v</code><dd>
 Writes the transferred data not only to their target streams, but also to
 stderr. The output format is text with some conversions for readability, and
 prefixed with "&gt; " or "&lt; " indicating flow directions.
<dt><code>-x</code><dd>
 Writes the transferred data not only to their target streams, but also to
 stderr. The output format is hexadecimal, prefixed with "&gt; " or "&lt; "
 indicating flow directions. Can be combined with 
<code>-v</code>
.
<dt><code>-r &lt;file&gt;</code><dd>
 Dumps the raw (binary) data flowing from left to right address to the given
 file.
<dt><code>-R &lt;file&gt;</code><dd>
 Dumps the raw (binary) data flowing from right to left address to the given
 file.
<a name="option_b"></a><dt><code>-b</code><code>&lt;size&gt;</code><dd>
 Sets the data transfer block &lt;size&gt; [<a href="socat.html#TYPE_SIZE_T">size_t</a>].
 At most &lt;size&gt; bytes are transferred per step. Default is 8192 bytes. 
<a name="option_s"></a><dt><code>-s</code><dd>
 By default, socat terminates when an error occurred to prevent the process
 from running when some option could not be applied. With this
 option, socat is sloppy with errors and tries to continue. Even with this
 option, socat will exit on fatals, and will abort connection attempts when
 security checks failed.
<a name="option_t"></a><dt><code>-t</code><code>&lt;timeout&gt;</code><dd>
 When one channel has reached EOF, the write part of the other channel is shut
 down. Then, socat waits &lt;timeout&gt; [<a href="socat.html#TYPE_TIMEVAL">timeval</a>] seconds
 before terminating. Default is 0.5 seconds. This timeout only applies to
 addresses where write and read part can be closed independently. When during
 the timeout interval the read part gives EOF, socat terminates without
 awaiting the timeout.
<a name="option_T"></a><dt><code>-T</code><code>&lt;timeout&gt;</code><dd>
 Total inactivity timeout: when socat is already in the transfer loop and
 nothing has happened for &lt;timeout&gt; [<a href="socat.html#TYPE_TIMEVAL">timeval</a>] seconds
 (no data arrived, no interrupt occurred...) then it terminates.
 Useful with protocols like UDP that cannot transfer EOF.
<a name="option_u"></a><dt><code>-u</code><dd>
 Uses unidirectional mode. The first address is only used for reading, and the
 second address is only used for writing (<a href="socat.html#EXAMPLE_option_u">example</a>). 
<a name="option_U"></a><dt><code>-U</code><dd>
 Uses unidirectional mode in reverse direction. The first address is only
 used for writing, and the second address is only used for reading. 
<a name="option_g"></a><dt><code>-g</code><dd>
 During address option parsing, don't check if the option is considered
 useful in the given address environment. Use it if you want to force, e.g.,
 appliance of a socket option to a serial device.
<a name="option_L"></a><dt><code>-L</code><code>&lt;lockfile&gt;</code><dd>
 If lockfile exists, exits with error. If lockfile does not exist, creates it
 and continues, unlinks lockfile on exit.
<a name="option_W"></a><dt><code>-W</code><code>&lt;lockfile&gt;</code><dd>
 If lockfile exists, waits until it disappears. When lockfile does not exist,
 creates it and continues, unlinks lockfile on exit.
<a name="option_4"></a><dt><code>-4</code><dd>
 Use IP version 4 in case that the addresses do not implicitly or explicitly
 specify a version; this is the default.
<a name="option_6"></a><dt><code>-6</code><dd>
 Use IP version 6 in case that the addresses do not implicitly or explicitly
 specify a version.
</dl>

<a name="ADDRESS_SPECIFICATIONS"></a>
<h2>ADDRESS SPECIFICATIONS</h2>

With the address command line arguments, the user gives socat instructions and
the necessary information for establishing the byte streams. 

An address specification usually consists of an address type
keyword, zero or more required address parameters separated by ':' from the keyword and
from each 
other, and zero or more address options separated by ','. 

The keyword specifies the address type (e.g., TCP4, OPEN, EXEC). For some
keywords there exist synonyms ('-' for STDIO, TCP for TCP4). Keywords are case
insensitive.
For a few special address types, the keyword may be omitted:
Address specifications starting with a number are assumed to be FD (raw file
descriptor) addresses; 
if a '/' is found before the first ':' or ',', GOPEN (generic file open) is
assumed. 

The required number and type of address parameters depend on the address
type. E.g., TCP4 requires a server specification (name or address), and a port
specification (number or service name). 

Zero or more address options may be given with each address. They influence the
address in some ways. 
Options consist of an option keyword or an option keyword and a value,
separated by '='. Option keywords are case insensitive.
For filtering the options that are useful with an address
type, each option is member of one option group. For
each address type there is a set of option groups allowed. Only options
belonging to one of these address groups may be used (except with <a href="socat.html#option_g">option -g</a>). 

<a name="ADDRESS_DUAL"></a>
Address specifications following the above schema are also called single
address specifications.
Two single addresses can be combined with "!!" to form a dual type
address for one channel. Here, the first address is used by socat for reading
data, and the 
second address for writing data. There is no way to specify an option only once
for being applied to both single addresses.

Usually, addresses are opened in read/write
mode. When an address is part of a dual address specification, or when
<a href="socat.html#option_u">option -u</a> or <a href="socat.html#option_U">-U</a> is used, an address might be
used only for reading or for writing. Considering this is important with some
address types.

With socat version 1.5.0 and higher, the lexical analysis tries to handle
quotes and parenthesis meaningfully and allows escaping of special characters. 
If one of the characters ( { [ ' is found, the corresponding closing 
character - ) } ] ' - is looked for; they may also be nested. Within these
constructs, socats special characters and strings : , !! are not handled
specially. All those characters and strings can be escaped with \ or within ""

<a name="ADDRESS_TYPES"></a>
<h2>ADDRESS TYPES</h2>

This section describes the available address types with their keywords,
parameters, and semantics.

<dl>
<a name="ADDRESS_CREAT"></a><dt><code>CREATE:&lt;filename&gt;</code><dd>
 Opens <a href="socat.html#TYPE_FILENAME">&lt;filename&gt;</a> with 
<code>creat()</code>
 and uses the file
 descriptor for writing. 
 This address type requires write-only context, because a file opened with
 
<code>creat</code>
 cannot be read from. 
 Flags like O_LARGEFILE cannot be applied. If you need them use
 <a href="socat.html#ADDRESS_OPEN">OPEN</a> with options
 <a href="socat.html#OPTION_O_CREAT">create</a>,<a href="socat.html#OPTION_O_TRUNC">create</a>. 
 &lt;filename&gt; must be a valid existing or not existing path.
 If &lt;filename&gt; is a named pipe, 
<code>creat()</code>
 might block;
 if &lt;filename&gt; refers to a socket, this is an error. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_REG">REG</a>,<a href="socat.html#GROUP_NAMED">NAMED</a> 
 Useful options:
 <a href="socat.html#OPTION_MODE">mode</a>,
 <a href="socat.html#OPTION_USER">user</a>,
 <a href="socat.html#OPTION_GROUP">group</a>,
 <a href="socat.html#OPTION_UNLINK_EARLY">unlink-early</a>,
 <a href="socat.html#OPTION_UNLINK_LATE">unlink-late</a>,
 <a href="socat.html#OPTION_APPEND">append</a> 
 See also: <a href="socat.html#ADDRESS_OPEN">OPEN</a>, <a href="socat.html#ADDRESS_GOPEN">GOPEN</a>
<a name="ADDRESS_EXEC"></a><dt><code>EXEC:&lt;command-line&gt;</code><dd>
 Forks a sub process that establishes communication with its parent process
 and invokes the specified program with 
<code>execvp()</code>
.
 <a href="socat.html#TYPE_COMMAND_LINE">&lt;command-line&gt;</a> is a simple command
 with arguments separated by single spaces. If the program name
 contains a '/', the part after the last '/' is taken as ARGV[0]. If the
 program name is a relative 
 path, the 
<code>execvp()</code>
 semantics for finding the program via
 
<code>$PATH</code>
 
 apply. After successful program start, socat writes data to stdin of the
 process and reads from its stdout using a UNIX domain socket generated by
 
<code>socketpair()</code>
 per default. (<a href="socat.html#EXAMPLE_ADDRESS_EXEC">example</a>) 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_EXEC">EXEC</a>,<a href="socat.html#GROUP_FORK">FORK</a>,<a href="socat.html#GROUP_TERMIOS">TERMIOS</a> 
 Useful options:
 <a href="socat.html#OPTION_PATH">path</a>,
 <a href="socat.html#OPTION_FDIN">fdin</a>,
 <a href="socat.html#OPTION_FDOUT">fdout</a>,
 <a href="socat.html#OPTION_CHROOT">chroot</a>,
 <a href="socat.html#OPTION_SUBSTUSER">su</a>,
 <a href="socat.html#OPTION_SUBSTUSER_DELAYED">su-d</a>,
 <a href="socat.html#OPTION_NOFORK">nofork</a>,
 <a href="socat.html#OPTION_PTY">pty</a>,
 <a href="socat.html#OPTION_STDERR">stderr</a>,
 <a href="socat.html#OPTION_CTTY">ctty</a>,
 <a href="socat.html#OPTION_SETSID">setsid</a>,
 <a href="socat.html#OPTION_PIPES">pipes</a>,
 <a href="socat.html#OPTION_LOGIN">login</a>,
 <a href="socat.html#OPTION_SIGINT">sigint</a>,
 <a href="socat.html#OPTION_SIGQUIT">sigquit</a> 
 See also: <a href="socat.html#ADDRESS_SYSTEM">SYSTEM</a>
<a name="ADDRESS_FD"></a><dt><code>FD:&lt;fdnum&gt;</code><dd>
 Uses the file descriptor <a href="socat.html#TYPE_FDNUM">&lt;fdnum&gt;</a>. It must already exist as
 valid UN*X file descriptor. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a> (<a href="socat.html#GROUP_TERMIOS">TERMIOS</a>,<a href="socat.html#GROUP_REG">REG</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>) 
 See also:
 <a href="socat.html#ADDRESS_STDIO">STDIO</a>,
 <a href="socat.html#ADDRESS_STDIN">STDIN</a>,
 <a href="socat.html#ADDRESS_STDOUT">STDOUT</a>,
 <a href="socat.html#ADDRESS_STDERR">STDERR</a> 
<a name="ADDRESS_GOPEN"></a><dt><code>GOPEN:&lt;filename&gt;</code><dd>
 (Generic open) This address type tries to handle any file system entry
 except directories usefully. <a href="socat.html#TYPE_FILENAME">&lt;filename&gt;</a> may be a
 relative or absolute path. If it already exists, its type is checked. 
 In case of a UNIX domain socket, socat connects; if connecting fails,
 socat assumes a datagram socket and uses 
<code>sendto()</code>
 calls.
 If the entry is not a socket, socat opens it applying the 
<code>O_APPEND</code>

flag. 
 If it does not exist, it is opened with flag
 
<code>O_CREAT</code>
 as a regular file (<a href="socat.html#EXAMPLE_ADDRESS_GOPEN">example</a>). 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_REG">REG</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_NAMED">NAMED</a>,<a href="socat.html#GROUP_OPEN">OPEN</a> 
 See also:
 <a href="socat.html#ADDRESS_OPEN">OPEN</a>,
 <a href="socat.html#ADDRESS_CREAT">CREATE</a>,
 <a href="socat.html#ADDRESS_UNIX_CONNECT">UNIX-CONNECT</a>

<a name="ADDRESS_IP_SENDTO"></a><dt><code>IP-SENDTO:&lt;host&gt;:&lt;protocol&gt;</code><dd>
 Opens a raw IP socket. Depending on host specification or option <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>, IP protocol version
 4 or 6 is used. It uses <a href="socat.html#TYPE_PROTOCOL">&lt;protocol&gt;</a> to send packets
 to &lt;host&gt; [<a href="socat.html#TYPE_IP_ADDRESS">IP address</a>] and receives packets from
 host, ignores packets from other hosts. 
 Protocol 255 uses the raw socket with the IP header being part of the
 data. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a> 
 Useful options:
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_TTL">ttl</a> 
 See also:
 <a href="socat.html#ADDRESS_IP4_SENDTO">IP4-SENDTO</a>,
 <a href="socat.html#ADDRESS_IP6_SENDTO">IP6-SENDTO</a>,
 <a href="socat.html#ADDRESS_IP_RECVFROM">IP-RECVFROM</a>,
 <a href="socat.html#ADDRESS_IP_RECV">IP-RECV</a>,
 <a href="socat.html#ADDRESS_UDP_SENDTO">UDP-SENDTO</a>,
 <a href="socat.html#ADDRESS_UNIX_SENDTO">UNIX-SENDTO</a>
<a name="ADDRESS_INTERFACE"></a><dt><code>INTERFACE:&lt;interface&gt;</code><dd>
 Communicates with a network connected on an interface using raw packets
 including link level data. <a href="socat.html#TYPE_INTERFACE">&lt;interface&gt;</a> is the name of
 the network interface. Currently only available on Linux.
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a> 
 Useful options:
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_SO_TYPE">type</a> 
 See also: <a href="socat.html#ADDRESS_IP_RECV">ip-recv</a>
<a name="ADDRESS_IP4_SENDTO"></a><dt><code>IP4-SENDTO:&lt;host&gt;:&lt;protocol&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_IP_SENDTO">IP-SENDTO</a>, but always uses IPv4. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a> 
<a name="ADDRESS_IP6_SENDTO"></a><dt><code>IP6-SENDTO:&lt;host&gt;:&lt;protocol&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_IP_SENDTO">IP-SENDTO</a>, but always uses IPv6. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP6">IP6</a> 

<a name="ADDRESS_IP_DATAGRAM"></a><dt><code>IP-DATAGRAM:&lt;address&gt;:&lt;protocol&gt;</code><dd>
 Sends outgoing data to the specified address which may in particular be a
 broadcast or multicast address. Packets arriving on the local socket are
 checked if their source addresses match
 <a href="socat.html#OPTION_RANGE">RANGE</a> or <a href="socat.html#OPTION_TCPWRAPPERS">TCPWRAP</a>
 options. This address type can for example be used for implementing
 symmetric or asymmetric broadcast or multicast communications. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>, <a href="socat.html#GROUP_SOCKET">SOCKET</a>,
 <a href="socat.html#GROUP_IP4">IP4</a>, <a href="socat.html#GROUP_IP6">IP6</a>, <a href="socat.html#GROUP_RANGE">RANGE</a> 
 Useful options:
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_RANGE">range</a>,
 <a href="socat.html#OPTION_TCPWRAPPERS">tcpwrap</a>,
 <a href="socat.html#OPTION_SO_BROADCAST">broadcast</a>,
 <a href="socat.html#OPTION_IP_MULTICAST_LOOP">ip-multicast-loop</a>,
 <a href="socat.html#OPTION_IP_MULTICAST_TTL">ip-multicast-ttl</a>,
 <a href="socat.html#OPTION_IP_MULTICAST_IF">ip-multicast-if</a>,
 <a href="socat.html#OPTION_IP_ADD_MEMBERSHIP">ip-add-membership</a>,
 <a href="socat.html#OPTION_IP_ADD_SOURCE_MEMBERSHIP">ip-add-source-membership</a>,
 <a href="socat.html#OPTION_TTL">ttl</a>,
 <a href="socat.html#OPTION_TOS">tos</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a> 
 See also:
 <a href="socat.html#ADDRESS_IP4_DATAGRAM">IP4-DATAGRAM</a>,
 <a href="socat.html#ADDRESS_IP6_DATAGRAM">IP6-DATAGRAM</a>,
 <a href="socat.html#ADDRESS_IP_SENDTO">IP-SENDTO</a>,
 <a href="socat.html#ADDRESS_IP_RECVFROM">IP-RECVFROM</a>,
 <a href="socat.html#ADDRESS_IP_RECV">IP-RECV</a>,
 <a href="socat.html#ADDRESS_UDP_DATAGRAM">UDP-DATAGRAM</a>
<a name="ADDRESS_IP4_DATAGRAM"></a><dt><code>IP4-DATAGRAM:&lt;host&gt;:&lt;protocol&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_IP_DATAGRAM">IP-DATAGRAM</a>, but always uses IPv4.
 (<a href="socat.html#EXAMPLE_ADDRESS_IP4_BROADCAST_CLIENT">example</a>) 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 
<a name="ADDRESS_IP6_DATAGRAM"></a><dt><code>IP6-DATAGRAM:&lt;host&gt;:&lt;protocol&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_IP_DATAGRAM">IP-DATAGRAM</a>, but always uses IPv6. Please
 note that IPv6 does not know broadcasts. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 

<a name="ADDRESS_IP_RECVFROM"></a><dt><code>IP-RECVFROM:&lt;protocol&gt;</code><dd>
 Opens a raw IP socket of <a href="socat.html#TYPE_PROTOCOL">&lt;protocol&gt;</a>. Depending on option <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>, IP protocol version
 4 or 6 is used. It receives one packet from an unspecified peer and may send one or more answer packets to that peer.
 This mode is particularly useful with fork option where each arriving packet - from arbitrary peers - is handled by its own sub process.
 This allows a behaviour similar to typical UDP based servers like ntpd or
 named. 
 Please note that the reply packets might be fetched as incoming traffic when
 sender and receiver IP address are identical because there is no port number
 to distinguish the sockets. 
 This address works well with IP-SENDTO address peers (see above).
 Protocol 255 uses the raw socket with the IP header being part of the
 data. 
 See the <a href="socat.html#NOTE_RECVFROM">note about RECVFROM addresses</a>. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 
 Useful options:
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_FORK">fork</a>,
 <a href="socat.html#OPTION_RANGE">range</a>,
 <a href="socat.html#OPTION_TTL">ttl</a>,
 <a href="socat.html#OPTION_SO_BROADCAST">broadcast</a> 
 See also:
 <a href="socat.html#ADDRESS_IP4_RECVFROM">IP4-RECVFROM</a>,
 <a href="socat.html#ADDRESS_IP6_RECVFROM">IP6-RECVFROM</a>,
 <a href="socat.html#ADDRESS_IP_SENDTO">IP-SENDTO</a>,
 <a href="socat.html#ADDRESS_IP_RECV">IP-RECV</a>,
 <a href="socat.html#ADDRESS_UDP_RECVFROM">UDP-RECVFROM</a>,
 <a href="socat.html#ADDRESS_UNIX_RECVFROM">UNIX-RECVFROM</a> 
<a name="ADDRESS_IP4_RECVFROM"></a><dt><code>IP4-RECVFROM:&lt;protocol&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_IP_RECVFROM">IP-RECVFROM</a>, but always uses IPv4. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 
<a name="ADDRESS_IP6_RECVFROM"></a><dt><code>IP6-RECVFROM:&lt;protocol&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_IP_RECVFROM">IP-RECVFROM</a>, but always uses IPv6. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 

<a name="ADDRESS_IP_RECV"></a><dt><code>IP-RECV:&lt;protocol&gt;</code><dd>
 Opens a raw IP socket of <a href="socat.html#TYPE_PROTOCOL">&lt;protocol&gt;</a>. Depending on option <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>, IP protocol version
 4 or 6 is used. It receives packets from multiple unspecified peers and merges the data.
 No replies are possible.
 It can be, e.g., addressed by socat IP-SENDTO address peers.
 Protocol 255 uses the raw socket with the IP header being part of the
 data. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 
 Useful options:
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_RANGE">range</a> 
 See also:
 <a href="socat.html#ADDRESS_IP4_RECV">IP4-RECV</a>,
 <a href="socat.html#ADDRESS_IP6_RECV">IP6-RECV</a>,
 <a href="socat.html#ADDRESS_IP_SENDTO">IP-SENDTO</a>,
 <a href="socat.html#ADDRESS_IP_RECVFROM">IP-RECVFROM</a>,
 <a href="socat.html#ADDRESS_UDP_RECV">UDP-RECV</a>,
 <a href="socat.html#ADDRESS_UNIX_RECV">UNIX-RECV</a> 
<a name="ADDRESS_IP4_RECV"></a><dt><code>IP4-RECV:&lt;protocol&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_IP_RECV">IP-RECV</a>, but always uses IPv4. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 
<a name="ADDRESS_IP6_RECV"></a><dt><code>IP6-RECV:&lt;protocol&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_IP_RECV">IP-RECV</a>, but always uses IPv6. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 

<a name="ADDRESS_OPEN"></a><dt><code>OPEN:&lt;filename&gt;</code><dd>
 Opens <a href="socat.html#TYPE_FILENAME">&lt;filename&gt;</a> using the 
<code>open()</code>
 system call
 (<a href="socat.html#EXAMPLE_ADDRESS_OPEN">example</a>).
 This operation fails on UNIX domain sockets. 
 Note: This address type is rarely useful in bidirectional mode. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_REG">REG</a>,<a href="socat.html#GROUP_NAMED">NAMED</a>,<a href="socat.html#GROUP_OPEN">OPEN</a> 
 Useful options:
 <a href="socat.html#OPTION_O_CREAT">creat</a>,
 <a href="socat.html#OPTION_EXCL">excl</a>,
 <a href="socat.html#OPTION_O_NOATIME">noatime</a>,
 <a href="socat.html#OPTION_NOFOLLOW">nofollow</a>,
 <a href="socat.html#OPTION_APPEND">append</a>,
 <a href="socat.html#OPTION_RDONLY">rdonly</a>,
 <a href="socat.html#OPTION_WRONLY">wronly</a>,
 <a href="socat.html#OPTION_LOCK">lock</a>,
 <a href="socat.html#OPTION_READBYTES">readbytes</a>,
 <a href="socat.html#OPTION_IGNOREEOF">ignoreeof</a> 
 See also:
 <a href="socat.html#ADDRESS_CREAT">CREATE</a>,
 <a href="socat.html#ADDRESS_GOPEN">GOPEN</a>,
 <a href="socat.html#ADDRESS_UNIX_CONNECT">UNIX-CONNECT</a>

<a name="ADDRESS_OPENSSL_CONNECT"></a><dt><code>OPENSSL:&lt;host&gt;:&lt;port&gt;</code><dd>
 Tries to establish a SSL connection to &lt;port&gt; [<a href="socat.html#TYPE_TCP_SERVICE">TCP
 service</a>] on 
 &lt;host&gt; [<a href="socat.html#TYPE_IP_ADDRESS">IP address</a>] using TCP/IP version 4 or 6
 depending on address specification, name resolution, or option
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>. 
 NOTE: Up to version 1.7.2.4
 the server certificate was only checked for validity against the system
 certificate store or <a href="socat.html#OPTION_OPENSSL_CAFILE">cafile</a> or
 <a href="socat.html#OPTION_OPENSSL_CAPATH">capath</a>,
 but not for match with the server's name or its IP address.
 Since version 1.7.3.0 socat checks the peer certificate for match with the
 &lt;host&gt; parameter or the value of the 
 <a href="socat.html#OPTION_OPENSSL_COMMONNAME">openssl-commonname</a> option.
 Socat tries to match it against the certificates subject commonName,
 and the certificates extension subjectAltName DNS names. Wildcards in the
 certificate are supported. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_TCP">TCP</a>,<a href="socat.html#GROUP_OPENSSL">OPENSSL</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_OPENSSL_CIPHERLIST">cipher</a>,
 <a href="socat.html#OPTION_OPENSSL_VERIFY">verify</a>,
 <a href="socat.html#OPTION_OPENSSL_COMMONNAME">commonname</a>,
 <a href="socat.html#OPTION_OPENSSL_CAFILE">cafile</a>,
 <a href="socat.html#OPTION_OPENSSL_CAPATH">capath</a>,
 <a href="socat.html#OPTION_OPENSSL_CERTIFICATE">certificate</a>,
 <a href="socat.html#OPTION_OPENSSL_KEY">key</a>,
 <a href="socat.html#OPTION_OPENSSL_COMPRESS">compress</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_CONNECT_TIMEOUT">connect-timeout</a>,
 <a href="socat.html#OPTION_SOURCEPORT">sourceport</a>,
 <a href="socat.html#OPTION_RETRY">retry</a> 
 See also:
 <a href="socat.html#ADDRESS_OPENSSL_LISTEN">OPENSSL-LISTEN</a>,
 <a href="socat.html#ADDRESS_TCP_CONNECT">TCP</a>

<a name="ADDRESS_OPENSSL_LISTEN"></a><dt><code>OPENSSL-LISTEN:&lt;port&gt;</code><dd>
 Listens on tcp &lt;port&gt; [<a href="socat.html#TYPE_TCP_SERVICE">TCP service</a>].
 The IP version is 4 or the one specified with
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>. When a
 connection is accepted, this address behaves as SSL server. 
 Note: You probably want to use the <a href="socat.html#OPTION_OPENSSL_CERTIFICATE">certificate</a> option with this address. 
 NOTE: The client certificate is only checked for validity against
 <a href="socat.html#OPTION_OPENSSL_CAFILE">cafile</a> or <a href="socat.html#OPTION_OPENSSL_CAPATH">capath</a>,
 but not for match with the client's name or its IP address! 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_TCP">TCP</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_OPENSSL">OPENSSL</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_OPENSSL_CIPHERLIST">cipher</a>,
 <a href="socat.html#OPTION_OPENSSL_VERIFY">verify</a>,
 <a href="socat.html#OPTION_OPENSSL_COMMONNAME">commonname</a>,
 <a href="socat.html#OPTION_OPENSSL_CAFILE">cafile</a>,
 <a href="socat.html#OPTION_OPENSSL_CAPATH">capath</a>,
 <a href="socat.html#OPTION_OPENSSL_CERTIFICATE">certificate</a>,
 <a href="socat.html#OPTION_OPENSSL_KEY">key</a>,
 <a href="socat.html#OPTION_OPENSSL_COMPRESS">compress</a>,
 <a href="socat.html#OPTION_FORK">fork</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_RANGE">range</a>,
 <a href="socat.html#OPTION_TCPWRAPPERS">tcpwrap</a>,
 <a href="socat.html#OPTION_SUBSTUSER">su</a>,
 <a href="socat.html#OPTION_REUSEADDR">reuseaddr</a>,
 <a href="socat.html#OPTION_RETRY">retry</a> 
 See also:
 <a href="socat.html#ADDRESS_OPENSSL_CONNECT">OPENSSL</a>,
 <a href="socat.html#ADDRESS_TCP_LISTEN">TCP-LISTEN</a>

<a name="ADDRESS_OPENSSL_DTLS_CLIENT"></a><dt><code>OPENSSL-DTLS-CLIENT:&lt;host&gt;:&lt;port&gt;</code><dd>
 Tries to establish a DTLS connection to &lt;port&gt; [<a href="socat.html#TYPE_UDP_SERVICE">UDP
 service</a>] on
 &lt;host&gt; [<a href="socat.html#TYPE_IP_ADDRESS">IP address</a>] using UDP/IP version 4 or 6
 depending on address specification, name resolution, or option
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>. 
 Socat checks the peer certificates subjectAltName or commonName against the addresses
 option <a href="socat.html#OPTION_OPENSSL_COMMONNAME">openssl-commonname</a> or the host name.
 Wildcards in the certificate are supported. 
 Use socat option <a href="socat.html#option_b">-b</a> to make datagrams small enough to fit with overhead
 on the network. Use option <a href="socat.html#option_T">-T</a> to prevent indefinite hanging when peer went down quietly. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_OPENSSL">OPENSSL</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_OPENSSL_CIPHERLIST">cipher</a>,
 <a href="socat.html#OPTION_OPENSSL_VERIFY">verify</a>,
 <a href="socat.html#OPTION_OPENSSL_COMMONNAME">commonname</a>,
 <a href="socat.html#OPTION_OPENSSL_CAFILE">cafile</a>,
 <a href="socat.html#OPTION_OPENSSL_CAPATH">capath</a>,
 <a href="socat.html#OPTION_OPENSSL_CERTIFICATE">certificate</a>,
 <a href="socat.html#OPTION_OPENSSL_KEY">key</a>,
 <a href="socat.html#OPTION_OPENSSL_COMPRESS">compress</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_SOURCEPORT">sourceport</a>,
 <a href="socat.html#OPTION_RETRY">retry</a> 
 See also:
 <a href="socat.html#ADDRESS_OPENSSL_DTLS_SERVER">OPENSSL-DTLS-SERVER</a>,
 <a href="socat.html#ADDRESS_OPENSSL_CONNECT">OPENSSL-CONNECT</a>,
 <a href="socat.html#ADDRESS_UDP_CONNECT">UDP-CONNECT</a>

<a name="ADDRESS_OPENSSL_DTLS_SERVER"></a><dt><code>OPENSSL-DTLS-SERVER:&lt;port&gt;</code><dd>
 Listens on UDP &lt;port&gt; [<a href="socat.html#TYPE_UDP_SERVICE">UDP service</a>].
 The IP version is 4 or the one specified with
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>. When a
 connection is accepted, this address behaves as DTLS server. 
 Note: You probably want to use the <a href="socat.html#OPTION_OPENSSL_CERTIFICATE">certificate</a> option with this address. 
 NOTE: The client certificate is only checked for validity against
 <a href="socat.html#OPTION_OPENSSL_CAFILE">cafile</a> or <a href="socat.html#OPTION_OPENSSL_CAPATH">capath</a>,
 but not for match with the client's name or its IP address!
 Use socat option <a href="socat.html#option_b">-b</a> to make datagrams small enough to fit with overhead on the network.
 Use option <a href="socat.html#option_T">-T</a> to prevent indefinite hanging when peer went down quietly. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_OPENSSL">OPENSSL</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_OPENSSL_CIPHERLIST">cipher</a>,
 <a href="socat.html#OPTION_OPENSSL_VERIFY">verify</a>,
 <a href="socat.html#OPTION_OPENSSL_COMMONNAME">commonname</a>,
 <a href="socat.html#OPTION_OPENSSL_CAFILE">cafile</a>,
 <a href="socat.html#OPTION_OPENSSL_CAPATH">capath</a>,
 <a href="socat.html#OPTION_OPENSSL_CERTIFICATE">certificate</a>,
 <a href="socat.html#OPTION_OPENSSL_KEY">key</a>,
 <a href="socat.html#OPTION_OPENSSL_COMPRESS">compress</a>,
 <a href="socat.html#OPTION_FORK">fork</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_RANGE">range</a>,
 <a href="socat.html#OPTION_TCPWRAPPERS">tcpwrap</a>,
 <a href="socat.html#OPTION_SUBSTUSER">su</a>,
 <a href="socat.html#OPTION_REUSEADDR">reuseaddr</a>,
 <a href="socat.html#OPTION_RETRY">retry</a> 
 See also:
 <a href="socat.html#ADDRESS_OPENSSL_DTLS_CLIENT">OPENSSL-DTLS-CLIENT</a>,
 <a href="socat.html#ADDRESS_OPENSSL_LISTEN">OPENSSL-LISTEN</a>,
 <a href="socat.html#ADDRESS_UDP_LISTEN">UDP-LISTEN</a>

<a name="ADDRESS_NAMED_PIPE"></a><dt><code>PIPE:&lt;filename&gt;</code><dd>
 If <a href="socat.html#TYPE_FILENAME">&lt;filename&gt;</a> already exists, it is opened.
 If it does not exist, a named pipe is created and opened. Beginning with
 socat version 1.4.3, the named pipe is removed when the address is closed
 (but see option <a href="socat.html#OPTION_UNLINK_CLOSE">unlink-close</a> 
 Note: When a pipe is used for both reading and writing, it works
 as echo service. 
 Note: When a pipe is used for both reading and writing, and socat tries
 to write more bytes than the pipe can buffer (Linux 2.4: 2048 bytes), socat
 might block. Consider using socat option, e.g., 
<code>-b 2048</code>
 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_NAMED">NAMED</a>,<a href="socat.html#GROUP_OPEN">OPEN</a> 
 Useful options:
 <a href="socat.html#OPTION_RDONLY">rdonly</a>,
 <a href="socat.html#OPTION_NONBLOCK">nonblock</a>,
 <a href="socat.html#OPTION_GROUP">group</a>,
 <a href="socat.html#OPTION_USER">user</a>,
 <a href="socat.html#OPTION_MODE">mode</a>,
 <a href="socat.html#OPTION_UNLINK_EARLY">unlink-early</a> 
 See also: <a href="socat.html#ADDRESS_UNNAMED_PIPE">unnamed pipe</a>
<a name="ADDRESS_UNNAMED_PIPE"></a><dt><code>PIPE</code><dd>
 Creates an unnamed pipe and uses it for reading and writing. It works as an
 echo, because everything written 
 to it appeares immediately as read data. 
 Note: When socat tries to write more bytes than the pipe can queue (Linux
 2.4: 2048 bytes), socat might block. Consider, e.g., using
 option 
<code>-b 2048</code>
 
 Option groups: <a href="socat.html#GROUP_FD">FD</a> 
 See also: <a href="socat.html#ADDRESS_NAMED_PIPE">named pipe</a>
<a name="ADDRESS_PROXY_CONNECT"></a><dt><code>PROXY:&lt;proxy&gt;:&lt;hostname&gt;:&lt;port&gt;</code><dd>
 Connects to an HTTP proxy server on port 8080 using TCP/IP version 4 or 6
 depending on address specification, name resolution, or option
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>, and sends a CONNECT
 request for hostname:port. If the proxy grants access and succeeds to
 connect to the target, data transfer between socat and the target can
 start. Note that the traffic need not be HTTP but can be an arbitrary
 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_TCP">TCP</a>,<a href="socat.html#GROUP_HTTP">HTTP</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_PROXYPORT">proxyport</a>,
 <a href="socat.html#OPTION_IGNORECR">ignorecr</a>,
 <a href="socat.html#OPTION_PROXY_AUTHORIZATION">proxyauth</a>,
 <a href="socat.html#OPTION_PROXY_RESOLVE">resolve</a>,
 <a href="socat.html#OPTION_CRNL">crnl</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_CONNECT_TIMEOUT">connect-timeout</a>,
 <a href="socat.html#OPTION_MSS">mss</a>,
 <a href="socat.html#OPTION_SOURCEPORT">sourceport</a>,
 <a href="socat.html#OPTION_RETRY">retry</a> 
 See also: <a href="socat.html#ADDRESS_SOCKS4">SOCKS</a>, <a href="socat.html#ADDRESS_TCP_CONNECT">TCP</a>
<a name="ADDRESS_PTY"></a><dt><code>PTY</code><dd>
 Generates a pseudo terminal (pty) and uses its master side. Another process
 may open the pty's slave side using it like a serial line or terminal.
 (<a href="socat.html#EXAMPLE_ADDRESS_PTY">example</a>). If
 both the ptmx and the openpty mechanisms are available, ptmx is used
 (POSIX). 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_NAMED">NAMED</a>,<a href="socat.html#GROUP_PTY">PTY</a>,<a href="socat.html#GROUP_TERMIOS">TERMIOS</a> 
 Useful options:
 <a href="socat.html#OPTION_SYMBOLIC_LINK">link</a>,
 <a href="socat.html#OPTION_OPENPTY">openpty</a>,
 <a href="socat.html#OPTION_PTY_WAIT_SLAVE">wait-slave</a>,
 <a href="socat.html#OPTION_MODE">mode</a>,
 <a href="socat.html#OPTION_USER">user</a>,
 <a href="socat.html#OPTION_GROUP">group</a> 
 See also:
 <a href="socat.html#ADDRESS_UNIX_LISTEN">UNIX-LISTEN</a>,
 <a href="socat.html#ADDRESS_NAMED_PIPE">PIPE</a>,
 <a href="socat.html#ADDRESS_EXEC">EXEC</a>, <a href="socat.html#ADDRESS_SYSTEM">SYSTEM</a>
<a name="ADDRESS_READLINE"></a><dt><code>READLINE</code><dd>
 Uses GNU readline and history on stdio to allow editing and reusing input
 lines (<a href="socat.html#EXAMPLE_ADDRESS_READLINE">example</a>). This requires the GNU readline and 
 history libraries. Note that stdio should be a (pseudo) terminal device,
 otherwise readline does not seem to work. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_READLINE">READLINE</a>,<a href="socat.html#GROUP_TERMIOS">TERMIOS</a> 
 Useful options:
 <a href="socat.html#OPTION_HISTORY">history</a>,
 <a href="socat.html#OPTION_NOECHO">noecho</a> 
 See also:
 <a href="socat.html#ADDRESS_STDIO">STDIO</a>
<a name="ADDRESS_SCTP_CONNECT"></a><dt><code>SCTP-CONNECT:&lt;host&gt;:&lt;port&gt;</code><dd>
 Establishes an SCTP stream connection to the specified &lt;host&gt; [<a href="socat.html#TYPE_IP_ADDRESS">IP
 address</a>] and &lt;port&gt; [<a href="socat.html#TYPE_TCP_SERVICE">TCP service</a>]
 using IP version 4 or 6 depending on address specification, name
 resolution, or option <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_SCTP">SCTP</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_CONNECT_TIMEOUT">connect-timeout</a>,
 <a href="socat.html#OPTION_TOS">tos</a>,
 <a href="socat.html#OPTION_MTUDISCOVER">mtudiscover</a>,
 <a href="socat.html#OPTION_SCTP_MAXSEG">sctp-maxseg</a>,
 <a href="socat.html#OPTION_SCTP_NODELAY">sctp-nodelay</a>,
 <a href="socat.html#OPTION_NONBLOCK">nonblock</a>,
 <a href="socat.html#OPTION_SOURCEPORT">sourceport</a>,
 <a href="socat.html#OPTION_RETRY">retry</a>,
 <a href="socat.html#OPTION_READBYTES">readbytes</a> 
 See also:
 <a href="socat.html#ADDRESS_SCTP4_CONNECT">SCTP4-CONNECT</a>,
 <a href="socat.html#ADDRESS_SCTP6_CONNECT">SCTP6-CONNECT</a>,
 <a href="socat.html#ADDRESS_SCTP_LISTEN">SCTP-LISTEN</a>,
 <a href="socat.html#ADDRESS_TCP_CONNECT">TCP-CONNECT</a>
<a name="ADDRESS_SCTP4_CONNECT"></a><dt><code>SCTP4-CONNECT:&lt;host&gt;:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_SCTP_CONNECT">SCTP-CONNECT</a>, but only supports IPv4 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_SCTP">SCTP</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
<a name="ADDRESS_SCTP6_CONNECT"></a><dt><code>SCTP6-CONNECT:&lt;host&gt;:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_SCTP_CONNECT">SCTP-CONNECT</a>, but only supports IPv6 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_SCTP">SCTP</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
<a name="ADDRESS_SCTP_LISTEN"></a><dt><code>SCTP-LISTEN:&lt;port&gt;</code><dd>
 Listens on &lt;port&gt; [<a href="socat.html#TYPE_TCP_SERVICE">TCP service</a>] and accepts an
 SCTP connection. The IP version is 4 or the one specified with
 address option <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>, socat option
 (<a href="socat.html#option_4">-4</a>, <a href="socat.html#option_6">-6</a>), or environment variable <a href="socat.html#ENV_SOCAT_DEFAULT_LISTEN_IP">SOCAT_DEFAULT_LISTEN_IP</a>.
 Note that opening
 this address usually blocks until a client connects. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_SCTP">SCTP</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_CRNL">crnl</a>,
 <a href="socat.html#OPTION_FORK">fork</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_RANGE">range</a>,
 <a href="socat.html#OPTION_TCPWRAPPERS">tcpwrap</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_MAX_CHILDREN">max-children</a>,
 <a href="socat.html#OPTION_BACKLOG">backlog</a>,
 <a href="socat.html#OPTION_ACCEPT_TIMEOUT">accept-timeout</a>,
 <a href="socat.html#OPTION_SCTP_MAXSEG">sctp-maxseg</a>,
 <a href="socat.html#OPTION_SCTP_NODELAY">sctp-nodelay</a>,
 <a href="socat.html#OPTION_SUBSTUSER">su</a>,
 <a href="socat.html#OPTION_REUSEADDR">reuseaddr</a>,
 <a href="socat.html#OPTION_RETRY">retry</a>,
 <a href="socat.html#OPTION_COOL_WRITE">cool-write</a> 
 See also:
 <a href="socat.html#ADDRESS_SCTP4_LISTEN">SCTP4-LISTEN</a>,
 <a href="socat.html#ADDRESS_SCTP6_LISTEN">SCTP6-LISTEN</a>,
 <a href="socat.html#ADDRESS_TCP_LISTEN">TCP-LISTEN</a>,
 <a href="socat.html#ADDRESS_SCTP_CONNECT">SCTP-CONNECT</a>
<a name="ADDRESS_SCTP4_LISTEN"></a><dt><code>SCTP4-LISTEN:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_SCTP_LISTEN">SCTP-LISTEN</a>, but only supports IPv4
 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_SCTP">SCTP</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
<a name="ADDRESS_SCTP6_LISTEN"></a><dt><code>SCTP6-LISTEN:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_SCTP_LISTEN">SCTP-LISTEN</a>, but only supports IPv6
 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_SCTP">SCTP</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
<a name="ADDRESS_SOCKET_CONNECT"></a><dt><code>SOCKET-CONNECT:&lt;domain&gt;:&lt;protocol&gt;:&lt;remote-address&gt;</code><dd>
 Creates a stream socket using the first and second given socket parameters
 and <code>SOCK_STREAM</code> (see man socket(2)) and connects to the remote-address.
 The two socket parameters have to be specified by <a href="socat.html#TYPE_INT">int</a>
 numbers. Consult your OS documentation and include files to find the
 appropriate values. The remote-address must be the <a href="socat.html#TYPE_DATA">data</a>
 representation of a sockaddr structure without sa_family and (BSD) sa_len
 components. 
 Please note that you can - beyond the options of the specified groups - also
 use options of higher level protocols when you apply socat option
 <a href="socat.html#option_g">-g</a>. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_SETSOCKOPT">setsockopt</a>,
 
 See also:
 <a href="socat.html#ADDRESS_TCP_CONNECT">TCP</a>,
 <a href="socat.html#ADDRESS_UDP_CONNECT">UDP-CONNECT</a>,
 <a href="socat.html#ADDRESS_UNIX_CONNECT">UNIX-CONNECT</a>,
 <a href="socat.html#ADDRESS_SOCKET_LISTEN">SOCKET-LISTEN</a>,
 <a href="socat.html#ADDRESS_SOCKET_SENDTO">SOCKET-SENDTO</a>
<a name="ADDRESS_SOCKET_DATAGRAM"></a><dt><code>SOCKET-DATAGRAM:&lt;domain&gt;:&lt;type&gt;:&lt;protocol&gt;:&lt;remote-address&gt;</code><dd>
 Creates a datagram socket using the first three given socket parameters (see
 man socket(2)) and sends outgoing data to the remote-address. The three
 socket parameters have to be specified by <a href="socat.html#TYPE_INT">int</a>
 numbers. Consult your OS documentation and include files to find the
 appropriate values. The remote-address must be the <a href="socat.html#TYPE_DATA">data</a>
 representation of a sockaddr structure without sa_family and (BSD) sa_len
 components. 
 Please note that you can - beyond the options of the specified groups - also
 use options of higher level protocols when you apply socat option
 <a href="socat.html#option_g">-g</a>. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 
 Useful options:
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_RANGE">range</a>,
 <a href="socat.html#OPTION_SETSOCKOPT">setsockopt</a>,
 
 See also:
 <a href="socat.html#ADDRESS_UDP_DATAGRAM">UDP-DATAGRAM</a>,
 <a href="socat.html#ADDRESS_IP_DATAGRAM">IP-DATAGRAM</a>,
 <a href="socat.html#ADDRESS_SOCKET_SENDTO">SOCKET-SENDTO</a>,
 <a href="socat.html#ADDRESS_SOCKET_RECV">SOCKET-RECV</a>,
 <a href="socat.html#ADDRESS_SOCKET_RECVFROM">SOCKET-RECVFROM</a>
<a name="ADDRESS_SOCKET_LISTEN"></a><dt><code>SOCKET-LISTEN:&lt;domain&gt;:&lt;protocol&gt;:&lt;local-address&gt;</code><dd>
 Creates a stream socket using the first and second given socket parameters
 and <code>SOCK_STREAM</code> (see man socket(2)) and waits for incoming connections
 on local-address. The two socket parameters have to be specified by
 <a href="socat.html#TYPE_INT">int</a> numbers. Consult your OS documentation and include files
 to find the appropriate values. The local-address must be the
 <a href="socat.html#TYPE_DATA">data</a> representation of a sockaddr structure without
 sa_family and (BSD) sa_len components. 
 Please note that you can - beyond the options of the specified groups - also
 use options of higher level protocols when you apply socat option
 <a href="socat.html#option_g">-g</a>. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_SETSOCKOPT">setsockopt</a>,
 <a href="socat.html#OPTION_SETSOCKOPT_LISTEN">setsockopt-listen</a>,
 
 See also:
 <a href="socat.html#ADDRESS_TCP_LISTEN">TCP</a>,
 <a href="socat.html#ADDRESS_UDP_LISTEN">UDP-CONNECT</a>,
 <a href="socat.html#ADDRESS_UNIX_LISTEN">UNIX-CONNECT</a>,
 <a href="socat.html#ADDRESS_SOCKET_CONNECT">SOCKET-LISTEN</a>,
 <a href="socat.html#ADDRESS_SOCKET_RECVFROM">SOCKET-SENDTO</a>,
 <a href="socat.html#ADDRESS_SOCKET_RECV">SOCKET-SENDTO</a>
<a name="ADDRESS_SOCKET_RECV"></a><dt><code>SOCKET-RECV:&lt;domain&gt;:&lt;type&gt;:&lt;protocol&gt;:&lt;local-address&gt;</code><dd>
 Creates a socket using the three given socket parameters (see man socket(2))
 and binds it to &lt;local-address&gt;. Receives arriving data. The three
 parameters have to be specified by <a href="socat.html#TYPE_INT">int</a> numbers. Consult your
 OS documentation and include files to find the appropriate values. The
 local-address must be the <a href="socat.html#TYPE_DATA">data</a> representation of a sockaddr
 structure without sa_family and (BSD) sa_len components. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 
 Useful options:
 <a href="socat.html#OPTION_RANGE">range</a>,
 <a href="socat.html#OPTION_SETSOCKOPT">setsockopt</a>,
 <a href="socat.html#OPTION_SETSOCKOPT_LISTEN">setsockopt-listen</a>
 
 See also:
 <a href="socat.html#ADDRESS_UDP_RECV">UDP-RECV</a>,
 <a href="socat.html#ADDRESS_IP_RECV">IP-RECV</a>,
 <a href="socat.html#ADDRESS_UNIX_RECV">UNIX-RECV</a>,
 <a href="socat.html#ADDRESS_SOCKET_DATAGRAM">SOCKET-DATAGRAM</a>,
 <a href="socat.html#ADDRESS_SOCKET_SENDTO">SOCKET-SENDTO</a>,
 <a href="socat.html#ADDRESS_SOCKET_RECVFROM">SOCKET-RECVFROM</a>
<a name="ADDRESS_SOCKET_RECVFROM"></a><dt><code>SOCKET-RECVFROM:&lt;domain&gt;:&lt;type&gt;:&lt;protocol&gt;:&lt;local-address&gt;</code><dd>
 Creates a socket using the three given socket parameters (see man socket(2))
 and binds it to &lt;local-address&gt;. Receives arriving data and sends replies
 back to the sender. The first three parameters have to be specified as
 <a href="socat.html#TYPE_INT">int</a> numbers. Consult your OS documentation and include files
 to find the appropriate values. The local-address must be the
 <a href="socat.html#TYPE_DATA">data</a> representation of a sockaddr structure without
 sa_family and (BSD) sa_len components. 
 See the <a href="socat.html#NOTE_RECVFROM">note about RECVFROM addresses</a>. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 
 Useful options:
 <a href="socat.html#OPTION_FORK">fork</a>,
 <a href="socat.html#OPTION_RANGE">range</a>,
 <a href="socat.html#OPTION_SETSOCKOPT">setsockopt</a>,
 <a href="socat.html#OPTION_SETSOCKOPT_LISTEN">setsockopt-listen</a>
 
 See also:
 <a href="socat.html#ADDRESS_UDP_RECVFROM">UDP-RECVFROM</a>,
 <a href="socat.html#ADDRESS_IP_RECVFROM">IP-RECVFROM</a>,
 <a href="socat.html#ADDRESS_UNIX_RECVFROM">UNIX-RECVFROM</a>,
 <a href="socat.html#ADDRESS_SOCKET_DATAGRAM">SOCKET-DATAGRAM</a>,
 <a href="socat.html#ADDRESS_SOCKET_SENDTO">SOCKET-SENDTO</a>,
 <a href="socat.html#ADDRESS_SOCKET_RECV">SOCKET-RECV</a>
<a name="ADDRESS_SOCKET_SENDTO"></a><dt><code>SOCKET-SENDTO:&lt;domain&gt;:&lt;type&gt;:&lt;protocol&gt;:&lt;remote-address&gt;</code><dd>
 Creates a socket using the three given socket parameters (see man
 socket(2)). Sends outgoing data to the given address and receives replies.
 The three parameters have to be specified as <a href="socat.html#TYPE_INT">int</a>
 numbers. Consult your OS documentation and include files to find the
 appropriate values. The remote-address must be the <a href="socat.html#TYPE_DATA">data</a>
 representation of a sockaddr structure without sa_family and (BSD) sa_len
 components. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a> 
 Useful options:
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_SETSOCKOPT">setsockopt</a>,
 <a href="socat.html#OPTION_SETSOCKOPT_LISTEN">setsockopt-listen</a>
 
 See also:
 <a href="socat.html#ADDRESS_UDP_SENDTO">UDP-SENDTO</a>,
 <a href="socat.html#ADDRESS_IP_SENDTO">IP-SENDTO</a>,
 <a href="socat.html#ADDRESS_UNIX_SENDTO">UNIX-SENDTO</a>,
 <a href="socat.html#ADDRESS_SOCKET_DATAGRAM">SOCKET-DATAGRAM</a>,
 <a href="socat.html#ADDRESS_SOCKET_RECV">SOCKET-RECV</a>
 <a href="socat.html#ADDRESS_SOCKET_RECVFROM">SOCKET-RECVFROM</a>
<a name="ADDRESS_SOCKS4"></a><dt><code>SOCKS4:&lt;socks-server&gt;:&lt;host&gt;:&lt;port&gt;</code><dd>
 Connects via &lt;socks-server&gt; [<a href="socat.html#TYPE_IP_ADDRESS">IP address</a>]
 to &lt;host&gt; [<a href="socat.html#TYPE_IPV4_ADDRESS">IPv4 address</a>]
 on &lt;port&gt; [<a href="socat.html#TYPE_TCP_SERVICE">TCP service</a>],
 using socks version 4 protocol over IP version 4 or 6 depending on address specification, name resolution, or option
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a> (<a href="socat.html#EXAMPLE_ADDRESS_SOCKS4">example</a>). 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_TCP">TCP</a>,<a href="socat.html#GROUP_SOCKS">SOCKS4</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_SOCKSUSER">socksuser</a>,
 <a href="socat.html#OPTION_SOCKSPORT">socksport</a>,
 <a href="socat.html#OPTION_SOURCEPORT">sourceport</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_RETRY">retry</a> 
 See also:
 <a href="socat.html#ADDRESS_SOCKS4A">SOCKS4A</a>,
 <a href="socat.html#ADDRESS_PROXY_CONNECT">PROXY</a>,
 <a href="socat.html#ADDRESS_TCP_CONNECT">TCP</a>
<a name="ADDRESS_SOCKS4A"></a><dt><code>SOCKS4A:&lt;socks-server&gt;:&lt;host&gt;:&lt;port&gt;</code><dd>
 like <a href="socat.html#ADDRESS_SOCKS4">SOCKS4</a>, but uses socks protocol version 4a, thus
 leaving host name resolution to the socks server. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_TCP">TCP</a>,<a href="socat.html#GROUP_SOCKS">SOCKS4</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
<a name="ADDRESS_STDERR"></a><dt><code>STDERR</code><dd>
 Uses file descriptor 2. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a> (<a href="socat.html#GROUP_TERMIOS">TERMIOS</a>,<a href="socat.html#GROUP_REG">REG</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>) 
 See also: <a href="socat.html#ADDRESS_FD">FD</a>
<a name="ADDRESS_STDIN"></a><dt><code>STDIN</code><dd>
 Uses file descriptor 0. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a> (<a href="socat.html#GROUP_TERMIOS">TERMIOS</a>,<a href="socat.html#GROUP_REG">REG</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>) 
 Useful options:
 <a href="socat.html#OPTION_READBYTES">readbytes</a> 
 See also: <a href="socat.html#ADDRESS_FD">FD</a>
<a name="ADDRESS_STDIO"></a><dt><code>STDIO</code><dd>
 Uses file descriptor 0 for reading, and 1 for writing. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a> (<a href="socat.html#GROUP_TERMIOS">TERMIOS</a>,<a href="socat.html#GROUP_REG">REG</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>) 
 Useful options:
 <a href="socat.html#OPTION_READBYTES">readbytes</a> 
 See also: <a href="socat.html#ADDRESS_FD">FD</a>
<a name="ADDRESS_STDOUT"></a><dt><code>STDOUT</code><dd>
 Uses file descriptor 1. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a> (<a href="socat.html#GROUP_TERMIOS">TERMIOS</a>,<a href="socat.html#GROUP_REG">REG</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>) 
 See also: <a href="socat.html#ADDRESS_FD">FD</a>
<a name="ADDRESS_SYSTEM"></a><dt><code>SYSTEM:&lt;shell-command&gt;</code><dd>
 Forks a sub process that establishes communication with its parent process
 and invokes the specified program with 
<code>system()</code>
. Please note that
 &lt;shell-command&gt; [<a href="socat.html#TYPE_STRING">string</a>] must 
 not contain ',' or "!!", and that shell meta characters may have to be
 protected.
 After successful program start, socat writes data to stdin of the 
 process and reads from its stdout. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_EXEC">EXEC</a>,<a href="socat.html#GROUP_FORK">FORK</a>,<a href="socat.html#GROUP_TERMIOS">TERMIOS</a> 
 Useful options:
 <a href="socat.html#OPTION_PATH">path</a>,
 <a href="socat.html#OPTION_FDIN">fdin</a>,
 <a href="socat.html#OPTION_FDOUT">fdout</a>,
 <a href="socat.html#OPTION_CHROOT">chroot</a>,
 <a href="socat.html#OPTION_SUBSTUSER">su</a>,
 <a href="socat.html#OPTION_SUBSTUSER_DELAYED">su-d</a>,
 <a href="socat.html#OPTION_NOFORK">nofork</a>,
 <a href="socat.html#OPTION_PTY">pty</a>,
 <a href="socat.html#OPTION_STDERR">stderr</a>,
 <a href="socat.html#OPTION_CTTY">ctty</a>,
 <a href="socat.html#OPTION_SETSID">setsid</a>,
 <a href="socat.html#OPTION_PIPES">pipes</a>,
 <a href="socat.html#OPTION_SIGINT">sigint</a>,
 <a href="socat.html#OPTION_SIGQUIT">sigquit</a> 
 See also: <a href="socat.html#ADDRESS_EXEC">EXEC</a>
<a name="ADDRESS_TCP_CONNECT"></a><dt><code>TCP:&lt;host&gt;:&lt;port&gt;</code><dd>
 Connects to &lt;port&gt; [<a href="socat.html#TYPE_TCP_SERVICE">TCP service</a>] on
 &lt;host&gt; [<a href="socat.html#TYPE_IP_ADDRESS">IP address</a>] using TCP/IP version 4 or 6
 depending on address specification, name resolution, or option
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_TCP">TCP</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_CRNL">crnl</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_CONNECT_TIMEOUT">connect-timeout</a>,
 <a href="socat.html#OPTION_TOS">tos</a>,
 <a href="socat.html#OPTION_MTUDISCOVER">mtudiscover</a>,
 <a href="socat.html#OPTION_MSS">mss</a>,
 <a href="socat.html#OPTION_TCP_NODELAY">nodelay</a>,
 <a href="socat.html#OPTION_NONBLOCK">nonblock</a>,
 <a href="socat.html#OPTION_SOURCEPORT">sourceport</a>,
 <a href="socat.html#OPTION_RETRY">retry</a>,
 <a href="socat.html#OPTION_READBYTES">readbytes</a> 
 See also:
 <a href="socat.html#ADDRESS_TCP4_CONNECT">TCP4</a>,
 <a href="socat.html#ADDRESS_TCP6_CONNECT">TCP6</a>,
 <a href="socat.html#ADDRESS_TCP_LISTEN">TCP-LISTEN</a>,
 <a href="socat.html#ADDRESS_UDP_CONNECT">UDP</a>,
 <a href="socat.html#ADDRESS_SCTP_CONNECT">SCTP-CONNECT</a>,
 <a href="socat.html#ADDRESS_UNIX_CONNECT">UNIX-CONNECT</a>
<a name="ADDRESS_TCP4_CONNECT"></a><dt><code>TCP4:&lt;host&gt;:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_TCP_CONNECT">TCP</a>, but only supports IPv4 protocol (<a href="socat.html#EXAMPLE_ADDRESS_TCP4_CONNECT">example</a>). 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_TCP">TCP</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
<a name="ADDRESS_TCP6_CONNECT"></a><dt><code>TCP6:&lt;host&gt;:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_TCP_CONNECT">TCP</a>, but only supports IPv6 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_TCP">TCP</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
<a name="ADDRESS_TCP_LISTEN"></a><dt><code>TCP-LISTEN:&lt;port&gt;</code><dd>
 Listens on &lt;port&gt; [<a href="socat.html#TYPE_TCP_SERVICE">TCP service</a>] and accepts a
 TCP/IP connection. The IP version is 4 or the one specified with
 address option <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>, socat option
 (<a href="socat.html#option_4">-4</a>, <a href="socat.html#option_6">-6</a>), or environment variable <a href="socat.html#ENV_SOCAT_DEFAULT_LISTEN_IP">SOCAT_DEFAULT_LISTEN_IP</a>.
 Note that opening
 this address usually blocks until a client connects. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_TCP">TCP</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_CRNL">crnl</a>,
 <a href="socat.html#OPTION_FORK">fork</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_RANGE">range</a>,
 <a href="socat.html#OPTION_TCPWRAPPERS">tcpwrap</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_MAX_CHILDREN">max-children</a>,
 <a href="socat.html#OPTION_BACKLOG">backlog</a>,
 <a href="socat.html#OPTION_ACCEPT_TIMEOUT">accept-timeout</a>,
 <a href="socat.html#OPTION_MSS">mss</a>,
 <a href="socat.html#OPTION_SUBSTUSER">su</a>,
 <a href="socat.html#OPTION_REUSEADDR">reuseaddr</a>,
 <a href="socat.html#OPTION_RETRY">retry</a>,
 <a href="socat.html#OPTION_COOL_WRITE">cool-write</a> 
 See also:
 <a href="socat.html#ADDRESS_TCP4_LISTEN">TCP4-LISTEN</a>,
 <a href="socat.html#ADDRESS_TCP6_LISTEN">TCP6-LISTEN</a>,
 <a href="socat.html#ADDRESS_UDP_LISTEN">UDP-LISTEN</a>,
 <a href="socat.html#ADDRESS_SCTP_LISTEN">SCTP-LISTEN</a>,
 <a href="socat.html#ADDRESS_UNIX_LISTEN">UNIX-LISTEN</a>,
 <a href="socat.html#ADDRESS_OPENSSL_LISTEN">OPENSSL-LISTEN</a>,
 <a href="socat.html#ADDRESS_TCP_CONNECT">TCP-CONNECT</a>
<a name="ADDRESS_TCP4_LISTEN"></a><dt><code>TCP4-LISTEN:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_TCP_LISTEN">TCP-LISTEN</a>, but only supports IPv4
 protocol (<a href="socat.html#EXAMPLE_ADDRESS_TCP4_LISTEN">example</a>). 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_TCP">TCP</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
<a name="ADDRESS_TCP6_LISTEN"></a><dt><code>TCP6-LISTEN:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_TCP_LISTEN">TCP-LISTEN</a>, but only supports IPv6
 protocol. 
 Additional useful option:
 <a href="socat.html#OPTION_IPV6_V6ONLY">ipv6only</a> 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_TCP">TCP</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
<a name="ADDRESS_TUN"></a><dt><code>TUN[:&lt;if-addr&gt;/&lt;bits&gt;]</code><dd>
 Creates a Linux TUN/TAP device and optionally assignes it the address and
 netmask given by the parameters. The resulting network interface is almost
 ready for use by other processes; socat serves its "wire side". This address
 requires read and write access to the tunnel cloning device, usually
 
<code>/dev/net/tun</code>
, as well as permission to set some <code>ioctl()s</code>.
 Option iff-up is required to immediately activate the interface! 
 Note: If you intend to transfer packets between two Socat "wire sides" you
 need a protocol that keeps packet boundaries, e.g.UDP; TCP might work with
 option <a href="socat.html#OPTION_TCP_NODELAY">nodelay</a>. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_NAMED">NAMED</a>,<a href="socat.html#GROUP_OPEN">OPEN</a>,<a href="socat.html#GROUP_TUN">TUN</a> 
 Useful options:
 <a href="socat.html#OPTION_IFF_UP">iff-up</a>,
 <a href="socat.html#OPTION_TUN_DEVICE">tun-device</a>,
 <a href="socat.html#OPTION_TUN_NAME">tun-name</a>,
 <a href="socat.html#OPTION_TUN_TYPE">tun-type</a>,
 <a href="socat.html#OPTION_IFF_NO_PI">iff-no-pi</a> 
 See also:
 <a href="socat.html#ADDRESS_IP_RECV">ip-recv</a>
<a name="ADDRESS_UDP_CONNECT"></a><dt><code>UDP:&lt;host&gt;:&lt;port&gt;</code><dd>
 Connects to &lt;port&gt; [<a href="socat.html#TYPE_UDP_SERVICE">UDP service</a>] on
 &lt;host&gt; [<a href="socat.html#TYPE_IP_ADDRESS">IP address</a>] using UDP/IP version 4 or 6
 depending on address specification, name resolution, or option
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>. 
 Please note that,
 due to UDP protocol properties, no real connection is established; data has
 to be sent for `connecting' to the server, and no end-of-file condition can
 be transported. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a> 
 Useful options:
 <a href="socat.html#OPTION_TTL">ttl</a>,
 <a href="socat.html#OPTION_TOS">tos</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_SOURCEPORT">sourceport</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a> 
 See also:
 <a href="socat.html#ADDRESS_UDP4_CONNECT">UDP4</a>,
 <a href="socat.html#ADDRESS_UDP6_CONNECT">UDP6</a>,
 <a href="socat.html#ADDRESS_UDP_LISTEN">UDP-LISTEN</a>,
 <a href="socat.html#ADDRESS_TCP_CONNECT">TCP</a>,
 <a href="socat.html#ADDRESS_IP_SENDTO">IP</a>
<a name="ADDRESS_UDP4_CONNECT"></a><dt><code>UDP4:&lt;host&gt;:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_UDP_CONNECT">UDP</a>, but only supports IPv4 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a> 
<a name="ADDRESS_UDP6_CONNECT"></a><dt><code>UDP6:&lt;host&gt;:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_UDP_CONNECT">UDP</a>, but only supports IPv6 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP6">IP6</a> 
<a name="ADDRESS_UDP_DATAGRAM"></a><dt><code>UDP-DATAGRAM:&lt;address&gt;:&lt;port&gt;</code><dd>
 Sends outgoing data to the specified address which may in particular be a
 broadcast or multicast address. Packets arriving on the local socket are
 checked for the correct remote port only when option <a href="socat.html#OPTION_SOURCEPORT">sourceport</a> is used (this is a change with Socat version 1.7.4.0) and if their source addresses match
 <a href="socat.html#OPTION_RANGE">RANGE</a> or <a href="socat.html#OPTION_TCPWRAPPERS">TCPWRAP</a>
 options. This address type can for example be used for implementing
 symmetric or asymmetric broadcast or multicast communications. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 
 Useful options:
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_RANGE">range</a>,
 <a href="socat.html#OPTION_TCPWRAPPERS">tcpwrap</a>,
 <a href="socat.html#OPTION_SO_BROADCAST">broadcast</a>,
 <a href="socat.html#OPTION_IP_MULTICAST_LOOP">ip-multicast-loop</a>,
 <a href="socat.html#OPTION_IP_MULTICAST_TTL">ip-multicast-ttl</a>,
 <a href="socat.html#OPTION_IP_MULTICAST_IF">ip-multicast-if</a>,
 <a href="socat.html#OPTION_IP_ADD_MEMBERSHIP">ip-add-membership</a>,
 <a href="socat.html#OPTION_IP_ADD_SOURCE_MEMBERSHIP">ip-add-source-membership</a>,
 <a href="socat.html#OPTION_TTL">ttl</a>,
 <a href="socat.html#OPTION_TOS">tos</a>,
 <a href="socat.html#OPTION_SOURCEPORT">sourceport</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a> 
 See also:
 <a href="socat.html#ADDRESS_UDP4_DATAGRAM">UDP4-DATAGRAM</a>,
 <a href="socat.html#ADDRESS_UDP6_DATAGRAM">UDP6-DATAGRAM</a>,
 <a href="socat.html#ADDRESS_UDP_SENDTO">UDP-SENDTO</a>,
 <a href="socat.html#ADDRESS_UDP_RECVFROM">UDP-RECVFROM</a>,
 <a href="socat.html#ADDRESS_UDP_RECV">UDP-RECV</a>,
 <a href="socat.html#ADDRESS_UDP_CONNECT">UDP-CONNECT</a>,
 <a href="socat.html#ADDRESS_UDP_LISTEN">UDP-LISTEN</a>,
 <a href="socat.html#ADDRESS_IP_DATAGRAM">IP-DATAGRAM</a>
<a name="ADDRESS_UDP4_DATAGRAM"></a><dt><code>UDP4-DATAGRAM:&lt;address&gt;:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_UDP_DATAGRAM">UDP-DATAGRAM</a>, but only supports IPv4
 protocol (<a href="socat.html#EXAMPLE_ADDRESS_UDP4_BROADCAST_CLIENT">example1</a>,
 <a href="socat.html#EXAMPLE_ADDRESS_UDP4_MULTICAST">example2</a>). 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>, <a href="socat.html#GROUP_RANGE">RANGE</a>
<a name="ADDRESS_UDP6_DATAGRAM"></a><dt><code>UDP6-DATAGRAM:&lt;address&gt;:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_UDP_DATAGRAM">UDP-DATAGRAM</a>, but only supports IPv6
 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>
<a name="ADDRESS_UDP_LISTEN"></a><dt><code>UDP-LISTEN:&lt;port&gt;</code><dd>
 Waits for a UDP/IP packet arriving on &lt;port&gt;
 [<a href="socat.html#TYPE_UDP_SERVICE">UDP service</a>] and `connects' back to sender.
 The accepted IP version is 4 or the one specified with option
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>.
 Please note that,
 due to UDP protocol properties, no real connection is established; data has
 to arrive from the peer first, and no end-of-file condition can be
 transported. Note that opening 
 this address usually blocks until a client connects. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a> 
 Useful options:
 <a href="socat.html#OPTION_FORK">fork</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_RANGE">range</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a> 
 See also:
 <a href="socat.html#ADDRESS_UDP_CONNECT">UDP</a>,
 <a href="socat.html#ADDRESS_UDP4_LISTEN">UDP4-LISTEN</a>,
 <a href="socat.html#ADDRESS_UDP6_LISTEN">UDP6-LISTEN</a>,
 <a href="socat.html#ADDRESS_TCP_LISTEN">TCP-LISTEN</a>
<a name="ADDRESS_UDP4_LISTEN"></a><dt><code>UDP4-LISTEN:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_UDP_LISTEN">UDP-LISTEN</a>, but only support IPv4
 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>,<a href="socat.html#GROUP_IP4">IP4</a> 
<a name="ADDRESS_UDP6_LISTEN"></a><dt><code>UDP6-LISTEN:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_UDP_LISTEN">UDP-LISTEN</a>, but only support IPv6
 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>,<a href="socat.html#GROUP_IP6">IP6</a> 
<a name="ADDRESS_UDP_SENDTO"></a><dt><code>UDP-SENDTO:&lt;host&gt;:&lt;port&gt;</code><dd>
 Communicates with the specified peer socket, defined by &lt;port&gt; [<a href="socat.html#TYPE_UDP_SERVICE">UDP
 service</a>] on
 &lt;host&gt; [<a href="socat.html#TYPE_IP_ADDRESS">IP address</a>], using UDP/IP version 4 or 6
 depending on address specification, name resolution, or option
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>. It sends packets to and receives packets
 from that peer socket only. 
 This address effectively implements a datagram client.
 It works well with socat UDP-RECVFROM and UDP-RECV address peers. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a> 
 Useful options:
 <a href="socat.html#OPTION_TTL">ttl</a>,
 <a href="socat.html#OPTION_TOS">tos</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_SOURCEPORT">sourceport</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a> 
 See also:
 <a href="socat.html#ADDRESS_UDP4_SENDTO">UDP4-SENDTO</a>,
 <a href="socat.html#ADDRESS_UDP6_SENDTO">UDP6-SENDTO</a>,
 <a href="socat.html#ADDRESS_UDP_RECVFROM">UDP-RECVFROM</a>,
 <a href="socat.html#ADDRESS_UDP_RECV">UDP-RECV</a>,
 <a href="socat.html#ADDRESS_UDP_CONNECT">UDP-CONNECT</a>,
 <a href="socat.html#ADDRESS_UDP_LISTEN">UDP-LISTEN</a>,
 <a href="socat.html#ADDRESS_IP_SENDTO">IP-SENDTO</a>
<a name="ADDRESS_UDP4_SENDTO"></a><dt><code>UDP4-SENDTO:&lt;host&gt;:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_UDP_SENDTO">UDP-SENDTO</a>, but only supports IPv4
 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>
<a name="ADDRESS_UDP6_SENDTO"></a><dt><code>UDP6-SENDTO:&lt;host&gt;:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_UDP_SENDTO">UDP-SENDTO</a>, but only supports IPv6
 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP6">IP6</a>

<a name="ADDRESS_UDP_RECVFROM"></a><dt><code>UDP-RECVFROM:&lt;port&gt;</code><dd>
 Creates a UDP socket on &lt;port&gt; [<a href="socat.html#TYPE_UDP_SERVICE">UDP service</a>] using
 UDP/IP version 4 or 6 
 depending on option <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>.
 It receives one packet from an unspecified peer and may send one or more
 answer packets to that peer. This mode is particularly useful with
 <a href="socat.html#OPTION_FORK">fork</a> option 
 where each arriving packet - from arbitrary peers - is handled by its own sub
 process. This allows a behaviour similar to typical UDP based servers like ntpd
 or named. This address works well with socat UDP-SENDTO address peers. 
 <a name="NOTE_RECVFROM"></a>Note: When the second address fails before entering the transfer loop the
 packet is dropped. Use option <a href="socat.html#OPTION_RETRY">retry</a> or
 <a href="socat.html#OPTION_FOREVER">forever</a> on the second address to avoid data loss.
 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 
 Useful options:
 <a href="socat.html#OPTION_FORK">fork</a>,
 <a href="socat.html#OPTION_TTL">ttl</a>,
 <a href="socat.html#OPTION_TOS">tos</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_SOURCEPORT">sourceport</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a> 
 See also:
 <a href="socat.html#ADDRESS_UDP4_RECVFROM">UDP4-RECVFROM</a>,
 <a href="socat.html#ADDRESS_UDP6_RECVFROM">UDP6-RECVFROM</a>,
 <a href="socat.html#ADDRESS_UDP_SENDTO">UDP-SENDTO</a>,
 <a href="socat.html#ADDRESS_UDP_RECV">UDP-RECV</a>,
 <a href="socat.html#ADDRESS_UDP_CONNECT">UDP-CONNECT</a>,
 <a href="socat.html#ADDRESS_UDP_LISTEN">UDP-LISTEN</a>,
 <a href="socat.html#ADDRESS_IP_RECVFROM">IP-RECVFROM</a>,
 <a href="socat.html#ADDRESS_UNIX_RECVFROM">UNIX-RECVFROM</a>
<a name="ADDRESS_UDP4_RECVFROM"></a><dt><code>UDP4-RECVFROM:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_UDP_RECVFROM">UDP-RECVFROM</a>, but only supports IPv4 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>
<a name="ADDRESS_UDP6_RECVFROM"></a><dt><code>UDP6-RECVFROM:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_UDP_RECVFROM">UDP-RECVFROM</a>, but only supports IPv6 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>

<a name="ADDRESS_UDP_RECV"></a><dt><code>UDP-RECV:&lt;port&gt;</code><dd>
 Creates a UDP socket on &lt;port&gt; [<a href="socat.html#TYPE_UDP_SERVICE">UDP service</a>] using UDP/IP version 4 or 6
 depending on option <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>.
 It receives packets from multiple unspecified peers and merges the data.
 No replies are possible. It works well with, e.g., socat <a href="socat.html#ADDRESS_UDP_SENDTO">UDP-SENDTO</a> address peers; it behaves similar to a syslog server. 
 Note: if you need the <a href="socat.html#OPTION_FORK">fork</a> option, use <a href="socat.html#ADDRESS_UDP_RECVFROM">UDP-RECVFROM</a> in unidirectional mode (with <a href="socat.html#option_u">option -u</a>) instead. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_RANGE">RANGE</a> 
 Useful options:
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_SOURCEPORT">sourceport</a>,
 <a href="socat.html#OPTION_TTL">ttl</a>,
 <a href="socat.html#OPTION_TOS">tos</a> 
 See also:
 <a href="socat.html#ADDRESS_UDP4_RECV">UDP4-RECV</a>,
 <a href="socat.html#ADDRESS_UDP6_RECV">UDP6-RECV</a>,
 <a href="socat.html#ADDRESS_UDP_SENDTO">UDP-SENDTO</a>,
 <a href="socat.html#ADDRESS_UDP_RECVFROM">UDP-RECVFROM</a>,
 <a href="socat.html#ADDRESS_UDP_CONNECT">UDP-CONNECT</a>,
 <a href="socat.html#ADDRESS_UDP_LISTEN">UDP-LISTEN</a>,
 <a href="socat.html#ADDRESS_IP_RECV">IP-RECV</a>,
 <a href="socat.html#ADDRESS_UNIX_RECV">UNIX-RECV</a>
<a name="ADDRESS_UDP4_RECV"></a><dt><code>UDP4-RECV:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_UDP_RECV">UDP-RECV</a>, but only supports IPv4 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP4">IP4</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>
<a name="ADDRESS_UDP6_RECV"></a><dt><code>UDP6-RECV:&lt;port&gt;</code><dd>
 Like <a href="socat.html#ADDRESS_UDP_RECV">UDP-RECV</a>, but only supports IPv6 protocol. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_IP6">IP6</a>,<a href="socat.html#GROUP_RANGE">RANGE</a>

<a name="ADDRESS_UNIX_CONNECT"></a><dt><code>UNIX-CONNECT:&lt;filename&gt;</code><dd>
 Connects to <a href="socat.html#TYPE_FILENAME">&lt;filename&gt;</a> assuming it is a UNIX domain
 socket.
 If &lt;filename&gt; does not exist, this is an error;
 if &lt;filename&gt; is not a UNIX domain socket, this is an error;
 if &lt;filename&gt; is a UNIX domain socket, but no process is listening, this is
 an error. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_NAMED">NAMED</a>,<a href="socat.html#GROUP_RETRY">RETRY</a>,<a href="socat.html#GROUP_SOCK_UNIX">UNIX</a> )
 Useful options:
 <a href="socat.html#OPTION_BIND">bind</a> 
 See also:
 <a href="socat.html#ADDRESS_UNIX_LISTEN">UNIX-LISTEN</a>,
 <a href="socat.html#ADDRESS_UNIX_SENDTO">UNIX-SENDTO</a>,
 <a href="socat.html#ADDRESS_TCP_CONNECT">TCP</a>

<a name="ADDRESS_UNIX_LISTEN"></a><dt><code>UNIX-LISTEN:&lt;filename&gt;</code><dd>
 Listens on <a href="socat.html#TYPE_FILENAME">&lt;filename&gt;</a> using a UNIX domain stream
 socket and accepts a connection.
 If &lt;filename&gt; exists and is not a socket, this is an error.
 If &lt;filename&gt; exists and is a UNIX domain socket, binding to the address
 fails (use option <a href="socat.html#OPTION_UNLINK_EARLY">unlink-early</a>!).
 Note that opening this address usually blocks until a client connects.
 Beginning with socat version 1.4.3, the file system entry is removed when
 this address is closed (but see option <a href="socat.html#OPTION_UNLINK_CLOSE">unlink-close</a>) (<a href="socat.html#EXAMPLE_ADDRESS_UNIX_LISTEN">example</a>). 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_NAMED">NAMED</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RETRY">RETRY</a>,<a href="socat.html#GROUP_SOCK_UNIX">UNIX</a> 
 Useful options:
 <a href="socat.html#OPTION_FORK">fork</a>,
 <a href="socat.html#OPTION_UMASK">umask</a>,
 <a href="socat.html#OPTION_MODE">mode</a>,
 <a href="socat.html#OPTION_USER">user</a>,
 <a href="socat.html#OPTION_GROUP">group</a>,
 <a href="socat.html#OPTION_UNLINK_EARLY">unlink-early</a> 
 See also:
 <a href="socat.html#ADDRESS_UNIX_CONNECT">UNIX-CONNECT</a>,
 <a href="socat.html#ADDRESS_UNIX_RECVFROM">UNIX-RECVFROM</a>,
 <a href="socat.html#ADDRESS_UNIX_RECV">UNIX-RECV</a>,
 <a href="socat.html#ADDRESS_TCP4_LISTEN">TCP-LISTEN</a>

<a name="ADDRESS_UNIX_SENDTO"></a><dt><code>UNIX-SENDTO:&lt;filename&gt;</code><dd>
 Communicates with the specified peer socket, defined by [<a href="socat.html#TYPE_FILENAME">&lt;filename&gt;</a>] assuming it is a UNIX domain datagram socket.
 It sends packets to and receives packets from that peer socket only.
 Please note that it might be necessary to <a href="socat.html#OPTION_BIND">bind</a> the
 local socket to an address (e.g. <code>/tmp/sock1</code>, which must not exist
 before).
 This address type works well with socat UNIX-RECVFROM and UNIX-RECV address
 peers. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_NAMED">NAMED</a>,<a href="socat.html#GROUP_SOCK_UNIX">UNIX</a> 
 Useful options:
 <a href="socat.html#OPTION_BIND">bind</a> 
 See also:
 <a href="socat.html#ADDRESS_UNIX_RECVFROM">UNIX-RECVFROM</a>,
 <a href="socat.html#ADDRESS_UNIX_RECV">UNIX-RECV</a>,
 <a href="socat.html#ADDRESS_UNIX_CONNECT">UNIX-CONNECT</a>,
 <a href="socat.html#ADDRESS_UDP_SENDTO">UDP-SENDTO</a>,
 <a href="socat.html#ADDRESS_IP_SENDTO">IP-SENDTO</a>

<a name="ADDRESS_UNIX_RECVFROM"></a><dt><code>UNIX-RECVFROM:&lt;filename&gt;</code><dd>
 Creates a UNIX domain datagram socket [<a href="socat.html#TYPE_FILENAME">&lt;filename&gt;</a>].
 Receives one packet and may send one or more answer packets to that peer.
 This mode is particularly useful with fork option where each arriving packet - from arbitrary peers - is handled by its own sub process.
 This address works well with socat UNIX-SENDTO address peers. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_NAMED">NAMED</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_SOCK_UNIX">UNIX</a> 
 See the <a href="socat.html#NOTE_RECVFROM">note about RECVFROM addresses</a>. 
 Useful options:
 <a href="socat.html#OPTION_FORK">fork</a> 
 See also:
 <a href="socat.html#ADDRESS_UNIX_SENDTO">UNIX-SENDTO</a>,
 <a href="socat.html#ADDRESS_UNIX_RECV">UNIX-RECV</a>,
 <a href="socat.html#ADDRESS_UNIX_LISTEN">UNIX-LISTEN</a>,
 <a href="socat.html#ADDRESS_UDP_RECVFROM">UDP-RECVFROM</a>,
 <a href="socat.html#ADDRESS_IP_RECVFROM">IP-RECVFROM</a>

<a name="ADDRESS_UNIX_RECV"></a><dt><code>UNIX-RECV:&lt;filename&gt;</code><dd>
 Creates a UNIX domain datagram socket [<a href="socat.html#TYPE_FILENAME">&lt;filename&gt;</a>].
 Receives packets from multiple unspecified peers and merges the data.
 No replies are possible. It can be, e.g., addressed by socat UNIX-SENDTO address peers.
 It behaves similar to a syslog server. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_NAMED">NAMED</a>,<a href="socat.html#GROUP_SOCK_UNIX">UNIX</a> 
 See also:
 <a href="socat.html#ADDRESS_UNIX_SENDTO">UNIX-SENDTO</a>,
 <a href="socat.html#ADDRESS_UNIX_RECVFROM">UNIX-RECVFROM</a>,
 <a href="socat.html#ADDRESS_UNIX_LISTEN">UNIX-LISTEN</a>,
 <a href="socat.html#ADDRESS_UDP_RECV">UDP-RECV</a>,
 <a href="socat.html#ADDRESS_IP_RECV">IP-RECV</a>

<a name="ADDRESS_UNIX_CLIENT"></a><dt><code>UNIX-CLIENT:&lt;filename&gt;</code><dd>
 Communicates with the specified peer socket, defined by
 [<a href="socat.html#TYPE_FILENAME">&lt;filename&gt;</a>] assuming it is a UNIX domain socket.
 It first tries to connect and, if that fails, assumes it is a datagram
 socket, thus supporting both types. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_NAMED">NAMED</a>,<a href="socat.html#GROUP_SOCK_UNIX">UNIX</a> 
 Useful options:
 <a href="socat.html#OPTION_BIND">bind</a> 
 See also:
 <a href="socat.html#ADDRESS_UNIX_CONNECT">UNIX-CONNECT</a>,
 <a href="socat.html#ADDRESS_UNIX_SENDTO">UNIX-SENDTO</a>,
 <a href="socat.html#ADDRESS_GOPEN">GOPEN</a>

<a name="ADDRESS_VSOCK_CONNECT"></a><dt><code>VSOCK-CONNECT:&lt;cid&gt;:&lt;port&gt;</code><dd>
 Establishes a VSOCK stream connection to the specified &lt;cid&gt; [<a href="socat.html#TYPE_VSOCK_ADDRESS">VSOCK
 cid</a>] and &lt;port&gt; [<a href="socat.html#TYPE_VSOCK_PORT">VSOCK port</a>]. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_CONNECT_TIMEOUT">connect-timeout</a>,
 <a href="socat.html#OPTION_RETRY">retry</a>,
 <a href="socat.html#OPTION_READBYTES">readbytes</a> 
 See also:
 <a href="socat.html#ADDRESS_VSOCK_LISTEN">VSOCK-LISTEN</a>,

<a name="ADDRESS_VSOCK_LISTEN"></a><dt><code>VSOCK-LISTEN:&lt;port&gt;</code><dd>
 Listens on &lt;port&gt; [<a href="socat.html#TYPE_VSOCK_PORT">VSOCK port</a>] and accepts a
 VSOCK connection.
 Note that opening this address usually blocks until a client connects. 
 Option groups: <a href="socat.html#GROUP_FD">FD</a>,<a href="socat.html#GROUP_SOCKET">SOCKET</a>,<a href="socat.html#GROUP_LISTEN">LISTEN</a>,<a href="socat.html#GROUP_CHILD">CHILD</a>,<a href="socat.html#GROUP_RETRY">RETRY</a> 
 Useful options:
 <a href="socat.html#OPTION_FORK">fork</a>,
 <a href="socat.html#OPTION_BIND">bind</a>,
 <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a>,
 <a href="socat.html#OPTION_MAX_CHILDREN">max-children</a>,
 <a href="socat.html#OPTION_BACKLOG">backlog</a>,
 <a href="socat.html#OPTION_SUBSTUSER">su</a>,
 <a href="socat.html#OPTION_REUSEADDR">reuseaddr</a>,
 <a href="socat.html#OPTION_RETRY">retry</a>,
 <a href="socat.html#OPTION_COOL_WRITE">cool-write</a> 
 See also:
 <a href="socat.html#ADDRESS_VSOCK_CONNECT">VSOCK-CONNECT</a>

<dt><code>ABSTRACT-CONNECT:&lt;string&gt;</code><dd>
<dt><code>ABSTRACT-LISTEN:&lt;string&gt;</code><dd>
<dt><code>ABSTRACT-SENDTO:&lt;string&gt;</code><dd>
<dt><code>ABSTRACT-RECVFROM:&lt;string&gt;</code><dd>
<dt><code>ABSTRACT-RECV:&lt;string&gt;</code><dd>
<dt><code>ABSTRACT-CLIENT:&lt;string&gt;</code><dd>
 The ABSTRACT addresses are almost identical to the related UNIX addresses
 except that they do not address file system based sockets but an alternate
 UNIX domain address space. To achieve this the socket address strings are
 prefixed with "\0" internally. This feature is available (only?) on Linux.
 Option groups are the same as with the related UNIX addresses, except that
 the ABSTRACT addresses are not member of the NAMED group.
</dl>

<a name="ADDRESS_OPTIONS"></a>
<h2>ADDRESS OPTIONS</h2>

Address options can be applied to address specifications to influence the
process of opening the addresses and the 
properties of the resulting data channels. 

For technical reasons not every option can be
applied to every address type; e.g., applying a socket option to a regular file
will fail. To catch most useless combinations as early as in the open phase,
the concept of option groups was introduced. Each option belongs to one
or more option groups. Options can be used only with address types that support
at least one of their option groups (but see <a href="socat.html#option_g">option -g</a>).

Address options have data types that their values must conform to. 
Every address option consists of just a keyword or a keyword followed by
"=value", where value must conform to the options type.

Some address options manipulate parameters of system calls;
e.g., option sync sets the 
<code>O_SYNC</code>
 flag with the 
<code>open()</code>
 call. 
Other options cause a system or library call; e.g., with option `ttl=value'
the 
<code>setsockopt(fd, SOL_IP, IP_TTL, value, sizeof(int))</code>
 call is applied.
Other
options set internal socat variables that are used during data transfer;
e.g., `crnl' causes explicit character conversions. 
A few options have more complex implementations; e.g., su-d
(substuser-delayed) inquires some user and group infos, stores them, and
applies them later after a possible 
<code>chroot()</code>
 call.

If multiple options are given to an address, their sequence in the address specification has (almost) no
effect on the sequence of their execution/application. Instead, socat has
built in an option phase model that tries to bring the options in a useful
order. Some options exist in different forms (e.g., 
unlink, unlink-early, unlink-late) to control the time of their execution.

If the same option is specified more than once within one address
specification, with equal or different values, the effect depends on the kind of option. Options
resulting in function calls like 
<code>setsockopt()</code>
 cause multiple
invocations. With options that set parameters for a required call like

<code>open()</code>
 
or set internal flags, the value of the last option occurrence is effective.

The existence or semantics of many options are system dependent. Socat
usually does NOT try to emulate missing libc or kernel features, it just
provides an 
interface to the underlying system. So, if an operating system lacks a feature,
the related option is simply not available on this platform.

The following paragraphs introduce just the more common address options. For
a more comprehensive reference and to find information about canonical option
names, alias names, option phases, and platforms see file xio.help. 
 

<dl></dl> 

<a name="GROUP_FD"></a>FD option group

This option group contains options that are applied to a UN*X
style file descriptor, no matter how it was generated.
Because all current socat address types are file descriptor based, these
options may be applied to any address. 
Note: Some of these options are also member of another option group, that
provides another, non-fd based mechanism.
For these options, it depends on the actual address type and its option groups 
which mechanism is used. The second, non-fd based mechanism is prioritized.
<dl>
<a name="OPTION_CLOEXEC"></a><dt><code>cloexec=&lt;bool&gt;</code><dd>
 Sets the 
<code>FD_CLOEXEC</code>
 flag with the 
<code>fcntl()</code>
 system call to value
 <a href="socat.html#TYPE_BOOL">&lt;bool&gt;</a>. If set,
 the file descriptor is closed on 
<code>exec()</code>
 family function calls. Socat
 internally handles 
 this flag for the fds it controls, so in most cases there will be no need to
 apply this option. 
<a name="OPTION_SETLK_WR"></a><dt><code>setlk</code><dd>
 Tries to set a discretionary write lock to the whole file using the 
<code>fcntl(fd,
 F_SETLK, ...)</code>
 system call. If the file is already locked, this call results
 in an error. 
 On Linux, when the file permissions for group are "S" (g-x,g+s), and the
 file system is locally mounted with the "mand" option, the lock is
 mandatory, i.e. prevents other processes from opening the file.
<a name="OPTION_SETLKW_WR"></a><dt><code>setlkw</code><dd>
 Tries to set a discretionary waiting write lock to the whole file using the
 
<code>fcntl(fd, F_SETLKW, ...)</code>
 system call. If the file is already locked,
 this call blocks. 
 See option <a href="socat.html#OPTION_SETLK_WR">setlk</a> for information about making this
 lock mandatory. 
<a name="OPTION_SETLK_RD"></a><dt><code>setlk-rd</code><dd>
 Tries to set a discretionary read lock to the whole file using the 
<code>fcntl(fd,
 F_SETLK, ...)</code>
 system call. If the file is already write locked, this call
 results in an error. 
 See option <a href="socat.html#OPTION_SETLK_WR">setlk</a> for information about making this
 lock mandatory. 
<a name="OPTION_SETLKW_RD"></a><dt><code>setlkw-rd</code><dd>
 Tries to set a discretionary waiting read lock to the whole file using the
 
<code>fcntl(fd, F_SETLKW, ...)</code>
 system call. If the file is already write
 locked, this call blocks. 
 See option <a href="socat.html#OPTION_SETLK_WR">setlk</a> for information about making this
 lock mandatory. 
<a name="OPTION_FLOCK_EX"></a><dt><code>flock-ex</code><dd>
 Tries to set a blocking exclusive advisory lock to the file using the
 
<code>flock(fd, LOCK_EX)</code>
 system call. Socat hangs in this call if the file
 is locked by another process.
<a name="OPTION_FLOCK_EX_NB"></a><dt><code>flock-ex-nb</code><dd>
 Tries to set a nonblocking exclusive advisory lock to the file using the
 
<code>flock(fd, LOCK_EX|LOCK_NB)</code>
 system call. If the file is already locked,
 this option results in an error.
<a name="OPTION_FLOCK_SH"></a><dt><code>flock-sh</code><dd>
 Tries to set a blocking shared advisory lock to the file using the
 
<code>flock(fd, LOCK_SH)</code>
 system call. Socat hangs in this call if the file
 is locked by another process.
<a name="OPTION_FLOCK_SH_NB"></a><dt><code>flock-sh-nb</code><dd>
 Tries to set a nonblocking shared advisory lock to the file using the
 
<code>flock(fd, LOCK_SH|LOCK_NB)</code>
 system call. If the file is already locked,
 this option results in an error.
<a name="OPTION_LOCK"></a><dt><code>lock</code><dd>
 Sets a blocking lock on the file. Uses the setlk or flock mechanism
 depending on availability on the particular platform. If both are available,
 the POSIX variant (setlkw) is used.
<a name="OPTION_USER"></a><dt><code>user=&lt;user&gt;</code><dd>
 Sets the <a href="socat.html#TYPE_USER">&lt;user&gt;</a> (owner) of the stream.
 If the address is member of the NAMED option group,
 socat uses the 
<code>chown()</code>
 system call after opening the
 file or binding to the UNIX domain socket (race condition!).
 Without filesystem entry, socat sets the user of the stream 
 using the 
<code>fchown()</code>
 system call.
 These calls might require root privilege. 
<a name="OPTION_USER_LATE"></a><dt><code>user-late=&lt;user&gt;</code><dd>
 Sets the owner of the fd to <a href="socat.html#TYPE_USER">&lt;user&gt;</a> with the 
<code>fchown()</code>

system call after opening 
 or connecting the channel.
 This is useful only on file system entries.
<a name="OPTION_GROUP"></a><dt><code>group=&lt;group&gt;</code><dd>
 Sets the <a href="socat.html#TYPE_GROUP">&lt;group&gt;</a> of the stream.
 If the address is member of the NAMED option group,
 socat uses the 
<code>chown()</code>
 system call after opening the
 file or binding to the UNIX domain socket (race condition!).
 Without filesystem entry, socat sets the group of the stream 
 with the 
<code>fchown()</code>
 system call. 
 These calls might require group membership or root privilege. 
<a name="OPTION_GROUP_LATE"></a><dt><code>group-late=&lt;group&gt;</code><dd>
 Sets the group of the fd to <a href="socat.html#TYPE_GROUP">&lt;group&gt;</a> with the
 
<code>fchown()</code>
 system call after opening 
 or connecting the channel.
 This is useful only on file system entries. 
<a name="OPTION_MODE"></a><dt><code>mode=&lt;mode&gt;</code><dd>
 Sets the &lt;mode&gt; [<a href="socat.html#TYPE_MODE_T">mode_t</a>] (permissions) of the stream.
 If the address is member of the NAMED option group and
 uses the 
<code>open()</code>
 or 
<code>creat()</code>
 call, the mode is applied with these.
 If the address is member of the NAMED option group without using these
 system calls, socat uses the 
<code>chmod()</code>
 system call after opening the
 filesystem entry or binding to the UNIX domain socket (race condition!).
 Otherwise, socat sets the mode of the stream
 using 
<code>fchmod()</code>
. 
 These calls might require ownership or root privilege.
<a name="OPTION_PERM_LATE"></a><dt><code>perm-late=&lt;mode&gt;</code><dd>
 Sets the permissions of the fd to value &lt;mode&gt;
 [<a href="socat.html#TYPE_MODE_T">mode_t</a>] using the 
<code>fchmod()</code>
 system call after
 opening or connecting the channel.
 This is useful only on file system entries. 
<a name="OPTION_APPEND"></a><dt><code>append=&lt;bool&gt;</code><dd>
 Always writes data to the actual end of file.
 If the address is member of the OPEN option group, 
 socat uses the 
<code>O_APPEND</code>
 flag with the 
<code>open()</code>
 system call
 (<a href="socat.html#EXAMPLE_OPTION_APPEND">example</a>).
 Otherwise, socat applies the 
<code>fcntl(fd, F_SETFL, O_APPEND)</code>
 call.
<a name="OPTION_NONBLOCK"></a><dt><code>nonblock=&lt;bool&gt;</code><dd>
 Tries to open or use file in nonblocking mode. Its only effects are that the
 
<code>connect()</code>
 call of TCP addresses does not block, and that opening a
 named pipe for reading does not block.
 If the address is member of the OPEN option group,
 socat uses the 
<code>O_NONBLOCK</code>
 flag with the 
<code>open()</code>
 system call.
 Otherwise, socat applies the 
<code>fcntl(fd, F_SETFL, O_NONBLOCK)</code>
 call.

<a name="OPTION_O_BINARY"></a><dt><code>binary</code><dd>
 Opens the file in binary mode to avoid implicit line terminator
 conversions (Cygwin).
<a name="OPTION_O_TEXT"></a><dt><code>text</code><dd>
 Opens the file in text mode to force implicit line terminator conversions
 (Cygwin).
<a name="OPTION_O_NOINHERIT"></a><dt><code>noinherit</code><dd>
 Does not keep this file open in a spawned process (Cygwin).
<a name="OPTION_COOL_WRITE"></a><dt><code>cool-write</code><dd>
 Takes it easy when write fails with EPIPE or ECONNRESET and logs the message
 with notice level instead of error.
 This prevents the log file from being filled with useless error messages
 when socat is used as a high volume server or proxy where clients often
 abort the connection. 
 This option is experimental.
<a name="OPTION_END_CLOSE"></a><dt><code>end-close</code><dd>
 Changes the (address dependent) method of ending a connection to just close
 the file descriptors. This is useful when the connection is to be reused by
 or shared with other processes (<a href="socat.html#EXAMPLE_END_CLOSE">example</a>). 
 Normally, socket connections will be ended with <code>shutdown(2)</code> which
 terminates the socket even if it is shared by multiple processes. 
 <code>close(2)</code> "unlinks" the socket from the process but keeps it active as
 long as there are still links from other processes. 
 Similarly, when an address of type EXEC or SYSTEM is ended, socat usually
 will explicitly kill the sub process. With this option, it will just close
 the file descriptors.
<a name="OPTION_SHUT_NONE"></a><dt><code>shut-none</code><dd>
 Changes the (address dependent) method of shutting down the write part of a
 connection to not do anything.
<a name="OPTION_SHUT_DOWN"></a><dt><code>shut-down</code><dd>
 Changes the (address dependent) method of shutting down the write part of a
 connection to shutdown(fd, SHUT_WR). Is only useful with sockets.
<a name="OPTION_SHUT_CLOSE"></a><dt><code>shut-close</code><dd>
 Changes the (address dependent) method of shutting down the write part of a
 connection to close(fd).
<a name="OPTION_SHUT_NULL"></a><dt><code>shut-null</code><dd>
 When one address indicates EOF, socat will send a zero sized packet to the
 write channel of the other address to transfer the EOF condition. This is
 useful with UDP and other datagram protocols. Has been tested against
 netcat and socat with option <a href="socat.html#OPTION_NULL_EOF">null-eof</a>.
<a name="OPTION_NULL_EOF"></a><dt><code>null-eof</code><dd>
 Normally socat will ignore empty (zero size payload) packets arriving on
 datagram sockets, so it survives port scans. With this option socat
 interprets empty datagram packets as EOF indicator (see
 <a href="socat.html#OPTION_SHUT_NULL">shut-null</a>).
<a name="OPTION_IOCTL_VOID"></a><dt><code>ioctl-void=&lt;request&gt;</code><dd>
 Calls <code>ioctl()</code> with the request value as second argument and NULL as
 third argument. This option allows utilizing ioctls that are not
 explicitly implemented in socat.
<a name="OPTION_IOCTL_INT"></a><dt><code>ioctl-int=&lt;request&gt;:&lt;value&gt;</code><dd>
 Calls <code>ioctl()</code> with the request value as second argument and the integer
 value as third argument.
<a name="OPTION_IOCTL_INTP"></a><dt><code>ioctl-intp=&lt;request&gt;:&lt;value&gt;</code><dd>
 Calls <code>ioctl()</code> with the request value as second argument and a pointer to
 the integer value as third argument.
<a name="OPTION_IOCTL_BIN"></a><dt><code>ioctl-bin=&lt;request&gt;:&lt;value&gt;</code><dd>
 Calls <code>ioctl()</code> with the request value as second argument and a pointer to
 the given data value as third argument. This data must be specified in
 <a href="socat.html#TYPE_DATA">&lt;dalan&gt;</a> form.
<a name="OPTION_IOCTL_STRING"></a><dt><code>ioctl-string=&lt;request&gt;:&lt;value&gt;</code><dd>
 Calls <code>ioctl()</code> with the request value as second argument and a pointer to
 the given string as third argument.
 <a href="socat.html#TYPE_DATA">&lt;dalan&gt;</a> form.
</dl>

<dl></dl> 

<a name="GROUP_NAMED"></a>NAMED option group

These options work on file system entries. 
Please note that, with UNIX domain client addresses, this means the bind entry,
not the target/peer entry. 
See also options <a href="socat.html#OPTION_USER">user</a>, <a href="socat.html#OPTION_GROUP">group</a>, and
<a href="socat.html#OPTION_MODE">mode</a>.

<dl>
<a name="OPTION_USER_EARLY"></a><dt><code>user-early=&lt;user&gt;</code><dd>
 Changes the <a href="socat.html#TYPE_USER">&lt;user&gt;</a> (owner) of the file system entry before
 accessing it, using the 
 
<code>chown()</code>
 system call. This call might require root privilege.
<a name="OPTION_GROUP_EARLY"></a><dt><code>group-early=&lt;group&gt;</code><dd>
 Changes the <a href="socat.html#TYPE_GROUP">&lt;group&gt;</a> of the file system entry before
 accessing it, using the 
 
<code>chown()</code>
 system call. This call might require group membership or root
 privilege. 
<a name="OPTION_PERM_EARLY"></a><dt><code>perm-early=&lt;mode&gt;</code><dd>
 Changes the &lt;mode&gt; [<a href="socat.html#TYPE_MODE_T">mode_t</a>] of the file system entry
 before accessing it, using the 
 
<code>chmod()</code>
 system call. This call might require ownership or root
 privilege. 
<a name="OPTION_UMASK"></a><dt><code>umask=&lt;mode&gt;</code><dd>
 Sets the umask of the process to &lt;mode&gt; [<a href="socat.html#TYPE_MODE_T">mode_t</a>] before
 accessing the file system entry (useful 
 with UNIX domain sockets!). This call might affect all further operations
 of the socat process! 
<a name="OPTION_UNLINK_EARLY"></a><dt><code>unlink-early</code><dd>
 Unlinks (removes) the file before opening it and even before applying
 user-early etc. 
<a name="OPTION_UNLINK"></a><dt><code>unlink</code><dd>
 Unlinks (removes) the file before accessing it, but after user-early etc.
<a name="OPTION_UNLINK_LATE"></a><dt><code>unlink-late</code><dd>
 Unlinks (removes) the file after opening it to make it inaccessible for
 other processes after a short race condition. 
<a name="OPTION_UNLINK_CLOSE"></a><dt><code>unlink-close</code><dd>
 Removes the addresses file system entry when closing the address.
 For <a href="socat.html#ADDRESS_NAMED_PIPE">named pipes</a>,
 <a href="socat.html#ADDRESS_UNIX_LISTEN">UNIX domain sockets</a>,
 and the <a href="socat.html#OPTION_SYMBOLIC_LINK">symbolic links</a> of <a href="socat.html#ADDRESS_PTY">pty addresses</a>,
 the default is 1; for <a href="socat.html#ADDRESS_CREAT">created files</a>,
 <a href="socat.html#ADDRESS_OPEN">opened files</a>, and
 <a href="socat.html#ADDRESS_GOPEN">generic opened files</a> the default is 0.
</dl>

<dl></dl> 

<a name="GROUP_OPEN"></a>OPEN option group

The OPEN group options allow setting flags with the 
<code>open()</code>
 system call. 
E.g., option `creat' sets the 
<code>O_CREAT</code>
 flag. 
See also options <a href="socat.html#OPTION_APPEND">append</a> and
<a href="socat.html#OPTION_NONBLOCK">nonblock</a>.
<dl>
<a name="OPTION_O_CREAT"></a><dt><code>creat=&lt;bool&gt;</code><dd>
 Creates the file if it does not exist (<a href="socat.html#EXAMPLE_OPTION_CREAT">example</a>).
<a name="OPTION_DSYNC"></a><dt><code>dsync=&lt;bool&gt;</code><dd>
 Blocks 
<code>write()</code>
 calls until metainfo is physically written to media.
<a name="OPTION_EXCL"></a><dt><code>excl=&lt;bool&gt;</code><dd>
 With option creat, if file exists this is an error.
<a name="OPTION_LARGEFILE"></a><dt><code>largefile=&lt;bool&gt;</code><dd>
 On 32 bit systems, allows a file larger than 2^31 bytes.
<a name="OPTION_O_NOATIME"></a><dt><code>noatime</code><dd>
 Sets the O_NOATIME options, so reads do not change the access timestamp.
<a name="OPTION_NOCTTY"></a><dt><code>noctty=&lt;bool&gt;</code><dd>
 Does not make this file the controlling terminal.
<a name="OPTION_NOFOLLOW"></a><dt><code>nofollow=&lt;bool&gt;</code><dd>
 Does not follow symbolic links.
<a name="OPTION_NSHARE"></a><dt><code>nshare=&lt;bool&gt;</code><dd>
 Does not allow sharing this file with other processes.
<a name="OPTION_RSHARE"></a><dt><code>rshare=&lt;bool&gt;</code><dd>
 Does not allow other processes to open this file for writing.
<a name="OPTION_RSYNC"></a><dt><code>rsync=&lt;bool&gt;</code><dd>
 Blocks 
<code>write()</code>
 until metainfo is physically written to media.
<a name="OPTION_SYNC"></a><dt><code>sync=&lt;bool&gt;</code><dd>
 Blocks 
<code>write()</code>
 until data is physically written to media.

<a name="OPTION_RDONLY"></a><dt><code>rdonly=&lt;bool&gt;</code><dd>
 Opens the file for reading only.

<a name="OPTION_WRONLY"></a><dt><code>wronly=&lt;bool&gt;</code><dd>
 Opens the file for writing only.
<a name="OPTION_O_TRUNC"></a><dt><code>trunc</code><dd>
 Truncates the file to size 0 during opening it.
</dl>

<dl></dl> 

<a name="GROUP_REG"></a>REG and BLK option group

These options are usually applied to a UN*X file descriptor, but their
semantics make sense only on a file supporting random access.
<dl>
<a name="OPTION_SEEK"></a><dt><code>seek=&lt;offset&gt;</code><dd>
 Applies the 
<code>lseek(fd, &lt;offset&gt;, SEEK_SET)</code>
 (or 
<code>lseek64</code>
) system
 call, thus positioning the file pointer absolutely to &lt;offset&gt;
 [<a href="socat.html#TYPE_OFF">off_t</a> or <a href="socat.html#TYPE_OFF64">off64_t</a>]. Please note that a
 missing value defaults to 1, not 0.
<a name="OPTION_SEEK_CUR"></a><dt><code>seek-cur=&lt;offset&gt;</code><dd>
 Applies the 
<code>lseek(fd, &lt;offset&gt;, SEEK_CUR)</code>
 (or 
<code>lseek64</code>
) system
 call, thus positioning the file pointer &lt;offset&gt; [<a href="socat.html#TYPE_OFF">off_t</a> or
 <a href="socat.html#TYPE_OFF64">off64_t</a>] bytes relatively to its current position (which
 is usually 0). Please note that a missing value defaults to 1, not 0.
<a name="OPTION_SEEK_END"></a><dt><code>seek-end=&lt;offset&gt;</code><dd>
 Applies the 
<code>lseek(fd, &lt;offset&gt;, SEEK_END)</code>
 (or 
<code>lseek64</code>
) system
 call, thus positioning the file pointer &lt;offset&gt; [<a href="socat.html#TYPE_OFF">off_t</a> or
 <a href="socat.html#TYPE_OFF64">off64_t</a>] bytes relatively to the files current end. Please
 note that a missing value defaults to 1, not 0. 
<a name="OPTION_FTRUNCATE"></a><dt><code>ftruncate=&lt;offset&gt;</code><dd>
 Applies the 
<code>ftruncate(fd, &lt;offset&gt;)</code>

(or 
<code>ftruncate64</code>
 if available) system call, thus
 truncating the file at the position &lt;offset&gt; [<a href="socat.html#TYPE_OFF">off_t</a> or 
 <a href="socat.html#TYPE_OFF64">off64_t</a>]. Please note that a missing value defaults to 1,
 not 0.

<a name="OPTION_FS_SECRM_FL"></a><dt><code>secrm=&lt;bool&gt;</code><dd>
<a name="OPTION_FS_UNRM"></a><dt><code>unrm=&lt;bool&gt;</code><dd>
<a name="OPTION_FS_COMPR"></a><dt><code>compr=&lt;bool&gt;</code><dd>
<a name="OPTION_FS_SYNC"></a><dt><code>fs-sync=&lt;bool&gt;</code><dd>
<a name="OPTION_FS_IMMUTABLE"></a><dt><code>immutable=&lt;bool&gt;</code><dd>
<a name="OPTION_FS_APPEND"></a><dt><code>fs-append=&lt;bool&gt;</code><dd>
<a name="OPTION_FS_NODUMP"></a><dt><code>nodump=&lt;bool&gt;</code><dd>
<a name="OPTION_FS_NOATIME"></a><dt><code>fs-noatime=&lt;bool&gt;</code><dd>
<a name="OPTION_FS_JOURNAL_DATA"></a><dt><code>journal-data=&lt;bool&gt;</code><dd>
<a name="OPTION_FS_NOTAIL"></a><dt><code>notail=&lt;bool&gt;</code><dd>
<a name="OPTION_FS_DIRSYNC"></a><dt><code>dirsync=&lt;bool&gt;</code><dd>
 These options change non standard file attributes on operating systems and
 file systems that support these features, like Linux with ext2fs and
 successors, xfs, or reiserfs. See man 1 chattr for information on these
 options. Please note that there might be a race condition between creating
 the file and applying these options.
</dl>

<dl></dl> 

<a name="GROUP_PROCESS"></a>PROCESS option group

Options of this group change the process properties instead of just affecting
one data channel.
For EXEC and SYSTEM addresses and for LISTEN and CONNECT type addresses with
option FORK, 
these options apply to the child processes instead of the main socat process.
<dl>
<a name="OPTION_CHROOT"></a><dt><code>chroot=&lt;directory&gt;</code><dd>
 Performs a 
<code>chroot()</code>
 operation to <a href="socat.html#TYPE_DIRECTORY">&lt;directory&gt;</a>
 after processing the address (<a href="socat.html#EXAMPLE_OPTION_CHROOT">example</a>). This call might require root privilege.
<a name="OPTION_CHROOT_EARLY"></a><dt><code>chroot-early=&lt;directory&gt;</code><dd>
 Performs a 
<code>chroot()</code>
 operation to <a href="socat.html#TYPE_DIRECTORY">&lt;directory&gt;</a>
 before opening the address. This call might require root privilege.
<a name="OPTION_SETGID"></a><dt><code>setgid=&lt;group&gt;</code><dd>
 Changes the primary <a href="socat.html#TYPE_GROUP">&lt;group&gt;</a> of the process after
 processing the address. This call might require root privilege. Please note
 that this option does not drop other group related privileges.
<a name="OPTION_SETGID_EARLY"></a><dt><code>setgid-early=&lt;group&gt;</code><dd>
 Like <a href="socat.html#OPTION_SETGID">setgit</a> but is performed before opening the address.
<a name="OPTION_SETUID"></a><dt><code>setuid=&lt;user&gt;</code><dd>
 Changes the <a href="socat.html#TYPE_USER">&lt;user&gt;</a> (owner) of the process after processing
 the address. This call might require root privilege. Please note that this
 option does not drop group related privileges. Check if option
 <a href="socat.html#OPTION_SUBSTUSER">su</a> better fits your needs.
<a name="OPTION_SETUID_EARLY"></a><dt><code>setuid-early=&lt;user&gt;</code><dd>
 Like <a href="socat.html#OPTION_SETUID">setuid</a> but is performed before opening the
 address.
<a name="OPTION_SUBSTUSER"></a><dt><code>su=&lt;user&gt;</code><dd>
 Changes the <a href="socat.html#TYPE_USER">&lt;user&gt;</a> (owner) and groups of the process after
 processing the address (<a href="socat.html#EXAMPLE_OPTION_SUBSTUSER">example</a>). This call might require root privilege. 
<a name="OPTION_SUBSTUSER_DELAYED"></a><dt><code>su-d=&lt;user&gt;</code><dd>
 Short name for <code>substuser-delayed</code>.
 
 Changes the <a href="socat.html#TYPE_USER">&lt;user&gt;</a>
 (owner) and groups of the process after processing the address (<a href="socat.html#EXAMPLE_OPTION_SUBSTUSER_DELAYED">example</a>).
 The user and his groups are retrieved before a possible
 
<code>chroot()</code>
. This call might require root privilege. 
<a name="OPTION_SETPGID"></a><dt><code>setpgid=&lt;pid_t&gt;</code><dd>
 Makes the process a member of the specified process group
 <a href="socat.html#TYPE_PID_T">&lt;pid_t&gt;</a>. If no value 
 is given, or if the value is 0 or 1, the process becomes leader of a new
 process group. 
<a name="OPTION_SETSID"></a><dt><code>setsid</code><dd>
 Makes the process the leader of a new session (<a href="socat.html#EXAMPLE_OPTION_SETSID">example</a>).
</dl>

<dl></dl> 

<a name="GROUP_READLINE"></a>READLINE option group

These options apply to the readline address type.
<dl>
<a name="OPTION_HISTORY"></a><dt><code>history=&lt;filename&gt;</code><dd>
 Reads and writes history from/to <a href="socat.html#TYPE_FILENAME">&lt;filename&gt;</a> (<a href="socat.html#EXAMPLE_OPTION_HISTORY">example</a>).
<a name="OPTION_NOPROMPT"></a><dt><code>noprompt</code><dd>
 Since version 1.4.0, socat per default tries to determine a prompt - 
 that is then passed to the readline call - by remembering the last
 incomplete line of the output. With this option, socat does not pass a
 prompt to readline, so it begins line editing in the first column
 of the terminal. 
<a name="OPTION_NOECHO"></a><dt><code>noecho=&lt;pattern&gt;</code><dd>
 Specifies a regular pattern for a prompt that prevents the following input
 line from being displayed on the screen and from being added to the history.
 The prompt is defined as the text that was output to the readline address 
 after the lastest newline character and before an input character was
 typed. The pattern is a regular expression, e.g.
 "^[Pp]assword:.*$" or "([Uu]ser:|[Pp]assword:)". See regex(7) for details.
 (<a href="socat.html#EXAMPLE_OPTION_NOECHO">example</a>)
<a name="OPTION_PROMPT"></a><dt><code>prompt=&lt;string&gt;</code><dd>
 Passes the string as prompt to the readline function. readline prints this
 prompt when stepping through the history. If this string matches a constant
 prompt issued by an interactive program on the other socat address,
 consistent look and feel can be achieved.
</dl>

<dl></dl> 

<a name="GROUP_APPLICATION"></a>APPLICATION option group

This group contains options that work at data level.
Note that these options only apply to the "raw" data transferred by socat,
but not to protocol data used by addresses like
<a href="socat.html#ADDRESS_PROXY_CONNECT">PROXY</a>.
<dl>
<a name="OPTION_CR"></a><dt><code>cr</code><dd>
 Converts the default line termination character NL ('\n', 0x0a) to/from CR
 ('\r', 0x0d) when writing/reading on this channel. 
<a name="OPTION_CRNL"></a><dt><code>crnl</code><dd>
 Converts the default line termination character NL ('\n', 0x0a) to/from CRNL
 ("\r\n", 0x0d0a) when writing/reading on this channel (<a href="socat.html#EXAMPLE_OPTION_CRNL">example</a>).
 Note: socat simply strips all CR characters.
<a name="OPTION_IGNOREEOF"></a><dt><code>ignoreeof</code><dd>
 When EOF occurs on this channel, socat ignores it and tries to read more
 data (like "tail -f") (<a href="socat.html#EXAMPLE_OPTION_IGNOREEOF">example</a>).
<a name="OPTION_READBYTES"></a><dt><code>readbytes=&lt;bytes&gt;</code><dd>
 socat reads only so many bytes from this address (the address provides
 only so many bytes for transfer and pretends to be at EOF afterwards).
 Must be greater than 0.
<a name="OPTION_LOCKFILE"></a><dt><code>lockfile=&lt;filename&gt;</code><dd>
 If lockfile exists, exits with error. If lockfile does not exist, creates it
 and continues, unlinks lockfile on exit.
<a name="OPTION_WAITLOCK"></a><dt><code>waitlock=&lt;filename&gt;</code><dd>
 If lockfile exists, waits until it disappears. When lockfile does not exist,
 creates it and continues, unlinks lockfile on exit.
<a name="OPTION_ESCAPE"></a><dt><code>escape=&lt;int&gt;</code><dd>
 Specifies the numeric code of a character that triggers EOF on the input
 stream. It is useful with a terminal in raw mode
 (<a href="socat.html#EXAMPLE_OPTION_ESCAPE">example</a>).
</dl>

<dl></dl> 

<a name="GROUP_SOCKET"></a>SOCKET option group

These options are intended for all kinds of sockets, e.g. IP or UNIX domain. Most are applied with a 
<code>setsockopt()</code>
 call.
<dl>
<a name="OPTION_BIND"></a><dt><code>bind=&lt;sockname&gt;</code><dd>
 Binds the socket to the given socket address using the 
<code>bind()</code>
 system
 call. The form of &lt;sockname&gt; is socket domain dependent:
 IP4 and IP6 allow the form [hostname|hostaddress][:(service|port)] (<a href="socat.html#EXAMPLE_OPTION_BIND_TCP4">example</a>),
 UNIX domain sockets require <a href="socat.html#TYPE_FILENAME">&lt;filename&gt;</a>,
 VSOCK allow the form [cid][:(port)].
<a name="OPTION_CONNECT_TIMEOUT"></a><dt><code>connect-timeout=&lt;seconds&gt;</code><dd>
 Abort the connection attempt after &lt;seconds&gt; [<a href="socat.html#TYPE_TIMEVAL">timeval</a>]
 with error status.
<a name="OPTION_SO_BINDTODEVICE"></a><dt><code>so-bindtodevice=&lt;interface&gt;</code><dd>
 Binds the socket to the given <a href="socat.html#TYPE_INTERFACE">&lt;interface&gt;</a>.
 This option might require root privilege.
<a name="OPTION_SO_BROADCAST"></a><dt><code>broadcast</code><dd>
 For datagram sockets, allows sending to broadcast addresses and receiving
 packets addressed to broadcast addresses.

<a name="OPTION_DEBUG"></a><dt><code>debug</code><dd>
 Enables socket debugging.
<a name="OPTION_DONTROUTE"></a><dt><code>dontroute</code><dd>
 Only communicates with directly connected peers, does not use routers.
<a name="OPTION_KEEPALIVE"></a><dt><code>keepalive</code><dd>
 Enables sending keepalives on the socket.
<a name="OPTION_LINGER"></a><dt><code>linger=&lt;seconds&gt;</code><dd>
 Blocks 
<code>shutdown()</code>
 or 
<code>close()</code>
 until data transfers have finished
 or the given timeout [<a href="socat.html#TYPE_INT">int</a>] expired.

<a name="OPTION_OOBINLINE"></a><dt><code>oobinline</code><dd>
 Places out-of-band data in the input data stream.
<a name="OPTION_PRIORITY"></a><dt><code>priority=&lt;priority&gt;</code><dd>
 Sets the protocol defined &lt;priority&gt; [<a href="socat.html#TYPE_INT">&lt;int&gt;</a>] for outgoing
 packets. 
<a name="OPTION_RCVBUF"></a><dt><code>rcvbuf=&lt;bytes&gt;</code><dd>
 Sets the size of the receive buffer after the 
<code>socket()</code>
 call to
 &lt;bytes&gt; [<a href="socat.html#TYPE_INT">int</a>]. With TCP
 sockets, this value corresponds to the socket's maximal window size.
<a name="OPTION_RCVBUF_LATE"></a><dt><code>rcvbuf-late=&lt;bytes&gt;</code><dd>
 Sets the size of the receive buffer when the socket is already
 connected to &lt;bytes&gt; [<a href="socat.html#TYPE_INT">int</a>]. 
 With TCP sockets, this value corresponds to the socket's 
 maximal window size. 
<a name="OPTION_RCVLOWAT"></a><dt><code>rcvlowat=&lt;bytes&gt;</code><dd>
 Specifies the minimum number of received bytes [<a href="socat.html#TYPE_INT">int</a>] until
 the socket layer will pass the buffered data to socat. 
<a name="OPTION_REUSEADDR"></a><dt><code>reuseaddr</code><dd>
 Allows other sockets to bind to an address even if parts of it (e.g. the
 local port) are already in use by socat (<a href="socat.html#EXAMPLE_OPTION_REUSEADDR">example</a>). 
<a name="OPTION_SNDBUF"></a><dt><code>sndbuf=&lt;bytes&gt;</code><dd>
 Sets the size of the send buffer after the 
<code>socket()</code>
 call to
 &lt;bytes&gt; [<a href="socat.html#TYPE_INT">int</a>].
<a name="OPTION_SNDBUF_LATE"></a><dt><code>sndbuf-late=&lt;bytes&gt;</code><dd>
 Sets the size of the send buffer when the socket is connected to
 &lt;bytes&gt; [<a href="socat.html#TYPE_INT">int</a>].
<a name="OPTION_SNDLOWAT"></a><dt><code>sndlowat=&lt;bytes&gt;</code><dd>
 Specifies the minimum number of bytes in the send buffer until the socket
 layer will send the data to &lt;bytes&gt; [<a href="socat.html#TYPE_INT">int</a>].
<a name="OPTION_PROTOCOL_FAMILY"></a><dt><code>pf=&lt;string&gt;</code><dd>
 Forces the use of the specified IP version or protocol. &lt;string&gt; can be
 something like "ip4" or "ip6". The resulting value is
 used as first argument to the 
<code>socket()</code>
 or 
<code>socketpair()</code>
 calls.
 This option affects address resolution and the required syntax of bind and
 range options.
<a name="OPTION_SO_TYPE"></a><dt><code>type=&lt;type&gt;</code><dd>
 Sets the type of the socket, specified as second argument to the
 
<code>socket()</code>
 or 
<code>socketpair()</code>
 calls, to &lt;type&gt;
 [<a href="socat.html#TYPE_INT">int</a>]. Address resolution is not affected by this option.
 Under Linux, 1 means stream oriented socket, 2 means datagram socket, and 3
 means raw socket.
<a name="OPTION_SO_PROTOCOL"></a><dt><code>protocol</code><dd>
 Sets the protocol of the socket, specified as third argument to the
 
<code>socket()</code>
 or 
<code>socketpair()</code>
 calls, to &lt;protocol&gt;
 [<a href="socat.html#TYPE_INT">int</a>]. Address resolution is not affected by this option.
 6 means TCP, 17 means UDP.

<a name="OPTION_REUSEPORT"></a><dt><code>reuseport</code><dd>
 Set the 
<code>SO_REUSEPORT</code>
 socket option.

<a name="OPTION_SO_TIMESTAMP"></a><dt><code>so-timestamp</code><dd>
 Sets the SO_TIMESTAMP socket option. This enables receiving and logging of
 timestamp ancillary messages.
<a name="OPTION_SETSOCKOPT"></a><dt><code>setsockopt=&lt;level&gt;:&lt;optname&gt;:&lt;optval&gt;</code><dd>
 Invokes <code>setsockopt()</code> for the socket with the given parameters. <code>level</code>
 [<a href="socat.html#TYPE_INT">int</a>] is used as second argument to <code>setsockopt()</code> and
 specifies the layer, e.g. SOL_TCP for TCP (6 on Linux), or SOL_SOCKET for
 the socket layer (1 on Linux). <code>optname</code> [<a href="socat.html#TYPE_INT">int</a>] is the
 third argument to <code>setsockopt()</code> and tells which socket option is to be
 set. For the actual numbers you might have to look up the appropriate include
 files of your system. For the 4th and 5th <code>setsockopt()</code> parameters,
 <code>value</code> [<a href="socat.html#TYPE_DATA">dalan</a>] specifies an arbitrary sequence of bytes
 that are passed to the function per pointer, with the automatically derived
 length parameter.
<a name="OPTION_SETSOCKOPT_INT"></a><dt><code>setsockopt-int=&lt;level&gt;:&lt;optname&gt;:&lt;optval&gt;</code><dd>
 Like <code>setsockopt</code>, but &lt;optval&gt; is a pointer to int [<a href="socat.html#TYPE_INT">int</a>]
<a name="OPTION_SETSOCKOPT_LISTEN"></a><dt><code>setsockopt-listen=&lt;level&gt;:&lt;optname&gt;:&lt;optval&gt;</code><dd>
 Like <code>setsockopt</code>, but for listen type addresses it is applied to the
 listening socket instead of the connected socket.
<a name="OPTION_SETSOCKOPT_STRING"></a><dt><code>setsockopt-string=&lt;level&gt;:&lt;optname&gt;:&lt;optval&gt;</code><dd>
 Like <code>setsockopt</code>, but &lt;optval&gt; is a <a href="socat.html#TYPE_STRING">string</a>.
 This string is passed to the function with trailing null character, and the
 length parameter is automatically derived from the data.
</dl>

<dl></dl> 

<a name="GROUP_SOCK_UNIX"></a>UNIX option group

These options apply to UNIX domain based addresses.
<dl>
<a name="OPTION_UNIX_TIGHTSOCKLEN"></a><dt><code>unix-tightsocklen=[0|1]</code><dd>
 On socket operations, pass a socket address length that does not include the
 whole 
<code>struct sockaddr_un</code>
 record but (besides other components) only
 the relevant part of the filename or abstract string. Default is 1.
</dl>

<a name="GROUP_IP4"></a>
<a name="GROUP_IP"></a>IP4 and IP6 option groups

These options can be used with IPv4 and IPv6 based sockets.
<dl>
<a name="OPTION_TOS"></a><dt><code>tos=&lt;tos&gt;</code><dd>
 Sets the TOS (type of service) field of outgoing packets to &lt;tos&gt;
 [<a href="socat.html#TYPE_BYTE">byte</a>] (see RFC 791).
<a name="OPTION_TTL"></a><dt><code>ttl=&lt;ttl&gt;</code><dd>
 Sets the TTL (time to live) field of outgoing packets to &lt;ttl&gt;
 [<a href="socat.html#TYPE_BYTE">byte</a>].
<a name="OPTION_IPOPTIONS"></a><dt><code>ip-options=&lt;data&gt;</code><dd>
 Sets IP options like source routing. Must be given in binary form,
 recommended format is a leading "x" followed by an even number of hex
 digits. This option may be used multiple times, data are appended.
 E.g., to connect to host 10.0.0.1 via some gateway using a loose source
 route, use the gateway as address parameter and set a loose source route
 using the option 
<code>ip-options=x8307040a000001</code>
. 
 IP options are defined in RFC 791.

<a name="OPTION_MTUDISCOVER"></a><dt><code>mtudiscover=&lt;0|1|2&gt;</code><dd>
 Takes 0, 1, 2 to never, want, or always use path MTU discover on this
 socket.

<a name="OPTION_IP_PKTINFO"></a><dt><code>ip-pktinfo</code><dd>
 Sets the IP_PKTINFO socket option. This enables receiving and logging of
 ancillary messages containing destination address and interface (Linux)
 (<a href="socat.html#EXAMPLE_ANCILLARY">example</a>).

<a name="OPTION_IP_RECVERR"></a><dt><code>ip-recverr</code><dd>
 Sets the IP_RECVERR socket option. This enables receiving and logging of
 ancillary messages containing detailed error information.
<a name="OPTION_IP_RECVOPTS"></a><dt><code>ip-recvopts</code><dd>
 Sets the IP_RECVOPTS socket option. This enables receiving and logging of IP
 options ancillary messages (Linux, *BSD).
<a name="OPTION_IP_RECVTOS"></a><dt><code>ip-recvtos</code><dd>
 Sets the IP_RECVTOS socket option. This enables receiving and logging of TOS
 (type of service) ancillary messages (Linux).
<a name="OPTION_IP_RECVTTL"></a><dt><code>ip-recvttl</code><dd>
 Sets the IP_RECVTTL socket option. This enables receiving and logging of TTL
 (time to live) ancillary messages (Linux, *BSD).

<a name="OPTION_IP_RECVDSTADDR"></a><dt><code>ip-recvdstaddr</code><dd>
 Sets the IP_RECVDSTADDR socket option. This enables receiving and logging of
 ancillary messages containing destination address (*BSD)
 (<a href="socat.html#EXAMPLE_ANCILLARY">example</a>).
<a name="OPTION_IP_RECVIF"></a><dt><code>ip-recvif</code><dd>
 Sets the IP_RECVIF socket option. This enables receiving and logging of
 interface ancillary messages (*BSD) (<a href="socat.html#EXAMPLE_ANCILLARY">example</a>).

<a name="OPTION_IP_ADD_MEMBERSHIP"></a>
<dt><code>ip-add-membership=&lt;multicast-address:interface-address&gt;</code><dd>
<dt><code>ip-add-membership=&lt;multicast-address:interface-name&gt;</code><dd>
<dt><code>ip-add-membership=&lt;multicast-address:interface-index&gt;</code><dd>
<dt><code>ip-add-membership=&lt;multicast-address:interface-address:interface-name&gt;</code><dd>
<dt><code>ip-add-membership=&lt;multicast-address:interface-address:interface-index&gt;</code><dd>
 Makes the socket member of the specified multicast group. This is currently
 only implemented for IPv4. The option takes the IP address of the multicast
 group and info about the desired network interface. The most common syntax
 is the first one, while the others are only available on systems that
 provide <code>struct mreqn</code> (Linux). 
 The indices of active network interfaces can be shown using the utility
 procan.
<a name="OPTION_IP_ADD_SOURCE_MEMBERSHIP"></a>
<dt><code>ip-add-source-membership=&lt;multicast-address:interface-address:source-address&gt;</code><dd>
 Makes the socket member of the specified multicast group for the specified
 source, i.e. only multicast traffic from this address is to be delivered.
 This is currently only implemented for IPv4. 
<a name="OPTION_IP_MULTICAST_IF"></a>
<dt><code>ip-multicast-if=&lt;hostname&gt;</code><dd>
 Specifies hostname or address of the network interface to be used for
 multicast traffic.
<a name="OPTION_IP_MULTICAST_LOOP"></a>
<dt><code>ip-multicast-loop=&lt;bool&gt;</code><dd>
 Specifies if outgoing multicast traffic should loop back to the interface.
<a name="OPTION_IP_MULTICAST_TTL"></a>
<dt><code>ip-multicast-ttl=&lt;byte&gt;</code><dd>
 Sets the TTL used for outgoing multicast traffic. Default is 1.
<a name="OPTOIN_IP_TRANSPARENT"></a>
<dt><code>ip-transparent</code><dd>
 Sets the IP_TRANSPARENT socket option.
 This option might require root privilege.
<a name="OPTION_RES_DEBUG"></a><dt><code>res-debug</code><dd>
<a name="OPTION_RES_AAONLY"></a><dt><code>res-aaonly</code><dd>
<a name="OPTION_RES_USEVC"></a><dt><code>res-usevc</code><dd>
<a name="OPTION_RES_PRIMARY"></a><dt><code>res-primary</code><dd>
<a name="OPTION_RES_IGNTC"></a><dt><code>res-igntc</code><dd>
<a name="OPTION_RES_RECURSE"></a><dt><code>res-recurse</code><dd>
<a name="OPTION_RES_DEFNAMES"></a><dt><code>res-defnames</code><dd>
<a name="OPTION_RES_STAYOPEN"></a><dt><code>res-stayopen</code><dd>
<a name="OPTION_RES_DNSRCH"></a><dt><code>res-dnsrch</code><dd>
 These options set the corresponding resolver (name resolution) option flags.
 Append "=0" to clear a default option. See man resolver(5) for more
 information on these options. Note: these options are valid only for the
 address they are applied to.

</dl>

<dl></dl> 

<a name="GROUP_IP6"></a>IP6 option group

These options can only be used on IPv6 based sockets. See <a href="socat.html#GROUP_IP">IP
options</a> for options that can be applied to both IPv4 and IPv6
sockets.
<dl>
<a name="OPTION_IPV6_V6ONLY"></a><dt><code>ipv6only=&lt;bool&gt;</code><dd>
 Sets the IPV6_V6ONLY socket option. If 0, the TCP stack will also accept
 connections using IPv4 protocol on the same port. The default is system
 dependent.
<a name="OPTION_IPV6_RECVDSTOPTS"></a><dt><code>ipv6-recvdstopts</code><dd>
 Sets the IPV6_RECVDSTOPTS socket option. This enables receiving and logging
 of ancillary messages containing the destination options.
<a name="OPTION_IPV6_RECVHOPLIMIT"></a><dt><code>ipv6-recvhoplimit</code><dd>
 Sets the IPV6_RECVHOPLIMIT socket option. This enables receiving and logging
 of ancillary messages containing the hoplimit.
<a name="OPTION_IPV6_RECVHOPOPTS"></a><dt><code>ipv6-recvhopopts</code><dd>
 Sets the IPV6_RECVHOPOPTS socket option. This enables receiving and logging
 of ancillary messages containing the hop options.
<a name="OPTION_IPV6_RECVPKTINFO"></a><dt><code>ipv6-recvpktinfo</code><dd>
 Sets the IPV6_RECVPKTINFO socket option. This enables receiving and logging
 of ancillary messages containing destination address and interface.
<a name="OPTION_IPV6_UNICAST_HOPS"></a><dt><code>ipv6-unicast-hops=link(TYPE_INT)(&lt;int&gt;)</code><dd>
 Sets the IPV6_UNICAST_HOPS socket option. This sets the hop count limit
 (TTL) for outgoing unicast packets.
<a name="OPTION_IPV6_RECVRTHDR"></a><dt><code>ipv6-recvrthdr</code><dd>
 Sets the IPV6_RECVRTHDR socket option. This enables receiving and logging
 of ancillary messages containing routing information.
<a name="OPTION_IPV6_TCLASS"></a><dt><code>ipv6-tclass</code><dd>
 Sets the IPV6_TCLASS socket option. This sets the transfer class of outgoing
 packets.
<a name="OPTION_IPV6_RECVTCLASS"></a><dt><code>ipv6-recvtclass</code><dd>
 Sets the IPV6_RECVTCLASS socket option. This enables receiving and logging
 of ancillary messages containing the transfer class.
</dl>

<dl></dl> 

<a name="GROUP_TCP"></a>TCP option group

These options may be applied to TCP sockets. They work by invoking 
<code>setsockopt()</code>
 with the appropriate parameters.
<dl>
<a name="OPTION_TCP_CORK"></a><dt><code>cork</code><dd>
 Doesn't send packets smaller than MSS (maximal segment size).
<a name="OPTION_DEFER-ACCEPT"></a><dt><code>defer-accept</code><dd>
 While listening, accepts connections only when data from the peer arrived.
<a name="OPTION_KEEPCNT"></a><dt><code>keepcnt=&lt;count&gt;</code><dd>
 Sets the number of keepalives before shutting down the socket to
 &lt;count&gt; [<a href="socat.html#TYPE_INT">int</a>].
<a name="OPTION_KEEPIDLE"></a><dt><code>keepidle=&lt;seconds&gt;</code><dd>
 Sets the idle time before sending the first keepalive to &lt;seconds&gt;
 [<a href="socat.html#TYPE_INT">int</a>].
<a name="OPTION_KEEPINTVL"></a><dt><code>keepintvl=&lt;seconds&gt;</code><dd>
 Sets the interval between two keepalives to &lt;seconds&gt;
 [<a href="socat.html#TYPE_INT">int</a>]. 
<a name="OPTION_LINGER2"></a><dt><code>linger2=&lt;seconds&gt;</code><dd>
 Sets the time to keep the socket in FIN-WAIT-2 state to &lt;seconds&gt;
 [<a href="socat.html#TYPE_INT">int</a>].
<a name="OPTION_MSS"></a><dt><code>mss=&lt;bytes&gt;</code><dd>
 Sets the MSS (maximum segment size) after the 
<code>socket()</code>
 call to &lt;bytes&gt;
 [<a href="socat.html#TYPE_INT">int</a>]. This
 value is then proposed to the peer with the SYN or SYN/ACK packet
 (<a href="socat.html#EXAMPLE_OPTION_MSS">example</a>). 
<a name="OPTION_MSS_LATE"></a><dt><code>mss-late=&lt;bytes&gt;</code><dd>
 Sets the MSS of the socket after connection has been established to &lt;bytes&gt;
 [<a href="socat.html#TYPE_INT">int</a>].
<a name="OPTION_TCP_NODELAY"></a><dt><code>nodelay</code><dd>
 Turns off the Nagle algorithm for measuring the RTT (round trip time).
<a name="OPTION_RFC1323"></a><dt><code>rfc1323</code><dd>
 Enables RFC1323 TCP options: TCP window scale, round-trip time measurement
 (RTTM), and protect against wrapped sequence numbers (PAWS) (AIX).
<a name="OPTION_STDURG"></a><dt><code>stdurg</code><dd>
 Enables RFC1122 compliant urgent pointer handling (AIX).
<a name="OPTION_SYNCNT"></a><dt><code>syncnt=&lt;count&gt;</code><dd>
 Sets the maximal number of SYN retransmits during connect to &lt;count&gt;
 [<a href="socat.html#TYPE_INT">int</a>].

<a name="OPTION_TCP_MD5SIG"></a><dt><code>md5sig</code><dd>
 Enables generation of MD5 digests on the packets (FreeBSD).
<a name="OPTION_TCP_NOOPT"></a><dt><code>noopt</code><dd>
 Disables use of TCP options (FreeBSD, MacOSX).
<a name="OPTION_TCP_NOPUSH"></a><dt><code>nopush</code><dd>
 sets the TCP_NOPUSH socket option (FreeBSD, MacOSX).
<a name="OPTION_TCP_SACK_DISABLE"></a><dt><code>sack-disable</code><dd>
 Disables use the selective acknowledge feature (OpenBSD).
<a name="OPTION_TCP_SIGNATURE_ENABLE"></a><dt><code>signature-enable</code><dd>
 Enables generation of MD5 digests on the packets (OpenBSD).
<a name="OPTION_TCP_ABORT_THRESHOLD"></a><dt><code>abort-threshold=&lt;milliseconds&gt;</code><dd>
 Sets the time to wait for an answer of the peer on an established connection
 (HP-UX).
<a name="OPTION_TCP_CONN_ABORT_THRESHOLD"></a><dt><code>conn-abort-threshold=&lt;milliseconds&gt;</code><dd>
 Sets the time to wait for an answer of the server during the initial connect
 (HP-UX).
<a name="OPTION_TCP_KEEPINIT"></a><dt><code>keepinit</code><dd>
 Sets the time to wait for an answer of the server during connect() before
 giving up. Value in half seconds, default is 150 (75s) (Tru64).
<a name="OPTION_TCP_PAWS"></a><dt><code>paws</code><dd>
 Enables the "protect against wrapped sequence numbers" feature (Tru64).
<a name="OPTION_TCP_SACKENA"></a><dt><code>sackena</code><dd>
 Enables selective acknowledge (Tru64).
<a name="OPTION_TCP_TSOPTENA"></a><dt><code>tsoptena</code><dd>
 Enables the time stamp option that allows RTT recalculation on existing
 connections (Tru64).
</dl>

<dl></dl> 

<a name="GROUP_UDP"></a>UDP option group

This option may be applied to UDP datagram sockets.

<dl>
<a name="OPTION_UDP_IGNORE_PEERPORT"></a><dt><code>udp-ignore-peerport&gt;</code><dd>
 Address UDP-DATAGRAM expects incoming responses to come from the port
 specified in its second parameter. With this option, it accepts packets
 coming from any port.
</dl>

<dl></dl> 

<a name="GROUP_SCTP"></a>SCTP option group

These options may be applied to SCTP stream sockets.
<dl>
<a name="OPTION_SCTP_NODELAY"></a><dt><code>sctp-nodelay</code><dd>
 Sets the SCTP_NODELAY socket option that disables the Nagle algorithm.
<a name="OPTION_SCTP_MAXSEG"></a><dt><code>sctp-maxseg=&lt;bytes&gt;</code><dd>
 Sets the SCTP_MAXSEG socket option to &lt;bytes&gt; [<a href="socat.html#TYPE_INT">int</a>]. This
 value is then proposed to the peer with the SYN or SYN/ACK packet. 
</dl>

<dl></dl> 

UDP, TCP, and SCTP option group

Here we find options that are related to the network port mechanism and thus
can be used with UDP, TCP, and SCTP client and server addresses.
<dl>
<a name="OPTION_SOURCEPORT"></a><dt><code>sourceport=&lt;port&gt;</code><dd>
 For outgoing (client) TCP and UDP connections, it sets the source
 <a href="socat.html#TYPE_PORT">&lt;port&gt;</a> using an extra 
<code>bind()</code>
 call.
 With TCP or UDP listen addresses, socat immediately shuts down the
 connection if the client does not use this sourceport. UDP-RECV,
 UDP-RECVFROM, UDP-SENDTO, and UDP-DATAGRAM addresses ignore the packet when
 it does not match.
 (<a href="socat.html#EXAMPLE_OPTION_SOURCEPORT">example</a>).
<a name="OPTION_LOWPORT"></a><dt><code>lowport</code><dd>
 Outgoing (client) TCP and UDP connections with this option use
 an unused random source port between 640 and 1023 incl. On UNIX class operating
 systems, this requires root privilege, and thus indicates that the
 client process is authorized by local root.
 TCP and UDP listen addresses with this option immediately shut down the
 connection if the client does not use a sourceport &lt;= 1023.
 This mechanism can provide limited authorization under some circumstances.
</dl>

<dl></dl> 

<a name="GROUP_SOCKS"></a>SOCKS option group

When using SOCKS type addresses, some socks specific options can be set.
<dl>
<a name="OPTION_SOCKSPORT"></a><dt><code>socksport=&lt;tcp service&gt;</code><dd>
 Overrides the default "socks" service or port 1080 for the socks server
 port with <a href="socat.html#TYPE_TCP_SERVICE">&lt;TCP service&gt;</a>.
<a name="OPTION_SOCKSUSER"></a><dt><code>socksuser=&lt;user&gt;</code><dd>
 Sends the &lt;user&gt; [<a href="socat.html#TYPE_STRING">string</a>] in the username field to the
 socks server. Default is the actual user name ($LOGNAME or $USER) (<a href="socat.html#EXAMPLE_OPTION_SOCKSUSER">example</a>).
</dl>

<dl></dl> 

<a name="GROUP_HTTP"></a>HTTP option group

Options that can be provided with HTTP type addresses. The only HTTP address
currently implemented is <a href="socat.html#ADDRESS_PROXY_CONNECT">proxy-connect</a>.

<dl>
<a name="OPTION_PROXYPORT"></a><dt><code>proxyport=&lt;TCP service&gt;</code><dd>
 Overrides the default HTTP proxy port 8080 with
 <a href="socat.html#TYPE_TCP_SERVICE">&lt;TCP service&gt;</a>.
<a name="OPTION_IGNORECR"></a><dt><code>ignorecr</code><dd>
 The HTTP protocol requires the use of CR+NL as line terminator. When a proxy
 server violates this standard, socat might not understand its answer. 
 This option directs socat to interprete NL as line terminator and
 to ignore CR in the answer. Nevertheless, socat sends CR+NL to the proxy.
<a name="OPTION_PROXY_AUTHORIZATION"></a><dt><code>proxy-authorization=&lt;username&gt;:&lt;password&gt;</code><dd>
 Provide "basic" authentication to the proxy server. The argument to the
 option is used with a "Proxy-Authorization: Basic" header in base64 encoded
 form. 
 Note: username and password are visible for every user on the local machine
 in the process list; username and password are transferred to the proxy
 server unencrypted (base64 encoded) and might be sniffed.
<a name="OPTION_PROXY_AUTHORIZATION_FILE"></a><dt><code>proxy-authorization-file=&lt;filename&gt;</code><dd>
 Like option <a href="socat.html#OPTION_PROXY_AUTHORIZATION">proxy-authorization</a>, but the
 credentials are read from the file and therefore not visible in the process
 list. 
<a name="OPTION_PROXY_RESOLVE"></a><dt><code>resolve</code><dd>
 Per default, socat sends to the proxy a CONNECT request containing the
 target hostname. With this option, socat resolves the hostname locally and
 sends the IP address. Please note that, according to RFC 2396, only name
 resolution to IPv4 addresses is implemented.
</dl>

<dl></dl> 

<a name="GROUP_RANGE"></a>RANGE option group

These options check if a connecting client should be granted access. They can
be applied to listening and receiving network sockets. tcp-wrappers options
fall into this group.
<dl>
<a name="OPTION_RANGE"></a><dt><code>range=&lt;address-range&gt;</code><dd>
 After accepting a connection, tests if the peer is within range. For
 IPv4 addresses, address-range takes the form address/bits, e.g.
 10.0.0.0/8, or address:mask, e.g. 10.0.0.0:255.0.0.0 (<a href="socat.html#EXAMPLE_OPTION_RANGE">example</a>); for IPv6, it is [ip6-address]/bits, e.g. [::1]/128.
 If the client address does not match, socat refuses the connection attempt, issues a warning, and keeps
 listening/receiving.
<a name="OPTION_TCPWRAPPERS"></a><dt><code>tcpwrap[=&lt;name&gt;]</code><dd>
 Uses Wietse Venema's libwrap (tcpd) library to determine
 if the client is allowed to connect. The configuration files are
 /etc/hosts.allow and /etc/hosts.deny per default, see "man 5 hosts_access"
 for more information. The optional &lt;name&gt; (type <a href="socat.html#TYPE_STRING">string</a>)
 is passed to the wrapper functions as daemon process name (<a href="socat.html#EXAMPLE_OPTION_TCPWRAPPERS">example</a>). 
 If omitted, the basename of socats invocation (argv[0]) is passed. 
 If both tcpwrap and range options are applied to an address, both
 conditions must be fulfilled to allow the connection.
<a name="OPTION_TCPWRAP_HOSTS_ALLOW_TABLE"></a><dt><code>allow-table=&lt;filename&gt;</code><dd>
 Takes the specified file instead of /etc/hosts.allow.
<a name="OPTION_TCPWRAP_HOSTS_DENY_TABLE"></a><dt><code>deny-table=&lt;filename&gt;</code><dd>
 Takes the specified file instead of /etc/hosts.deny.
<a name="OPTION_TCPWRAP_ETC"></a><dt><code>tcpwrap-etc=&lt;directoryname&gt;</code><dd>
 Looks for hosts.allow and hosts.deny in the specified directory. Is
 overridden by options <a href="socat.html#OPTION_TCPWRAP_HOSTS_ALLOW_TABLE">hosts-allow</a>
 and <a href="socat.html#OPTION_TCPWRAP_HOSTS_DENY_TABLE">hosts-deny</a>.
</dl>

<dl></dl> 

<a name="GROUP_LISTEN"></a>LISTEN option group

Options specific to listening sockets.
<dl>
<a name="OPTION_BACKLOG"></a><dt><code>backlog=&lt;count&gt;</code><dd>
 Sets the backlog value passed with the 
<code>listen()</code>
 system call to &lt;count&gt;
 [<a href="socat.html#TYPE_INT">int</a>]. Default is 5. 
<a name="OPTION_ACCEPT_TIMEOUT"></a><dt><code>accept-timeout=&lt;seconds&gt;</code><dd>
 End waiting for a connection after &lt;seconds&gt; [<a href="socat.html#TYPE_TIMEVAL">timeval</a>]
 with error status.
<a name="OPTION_MAX_CHILDREN"></a><dt><code>max-children=&lt;count&gt;</code><dd>
 Limits the number of concurrent child processes [<a href="socat.html#TYPE_INT">int</a>].
 Default is no limit. 
</dl>
<dl></dl> 

<a name="GROUP_CHILD"></a>CHILD option group

Options for addresses with multiple connections via child processes.
<dl>
<a name="OPTION_FORK"></a><dt><code>fork</code><dd>
 After establishing a connection, handles its channel in a child process and
 keeps the parent process attempting to produce more connections, either by
 listening or by connecting in a loop (<a href="socat.html#EXAMPLE_OPTION_FORK">example</a>). 
 OPENSSL-CONNECT and OPENSSL-LISTEN differ in when they actually fork off the
 child:
 OPENSSL-LISTEN forks before the SSL handshake, while OPENSSL-CONNECT
 forks afterwards.
 <a href="socat.html#OPTION_RETRY">retry</a> and <a href="socat.html#OPTION_FOREVER">forever</a> options are not
 inherited by the child process. 
 On some operating systems (e.g. FreeBSD) this option does not work for
 UDP-LISTEN addresses. 
</dl>

<dl></dl> 

<a name="GROUP_EXEC"></a>EXEC option group

Options for addresses that invoke a program.
<dl>
<a name="OPTION_PATH"></a><dt><code>path=&lt;string&gt;</code><dd>
 Overrides the PATH environment variable for searching the program with
 <a href="socat.html#TYPE_STRING">&lt;string&gt;</a>. This
 
<code>$PATH</code>
 value is effective in the child process too.
<a name="OPTION_LOGIN"></a><dt><code>login</code><dd>
 Prefixes 
<code>argv[0]</code>
 for the 
<code>execvp()</code>
 call with '-', thus making a
 shell behave as login shell.
</dl>

<dl></dl> 

<a name="GROUP_FORK"></a>FORK option group

EXEC or SYSTEM addresses invoke a program using a child process and transfer data between socat and the program. The interprocess communication mechanism can be influenced with the following options. Per
default, a 
<code>socketpair()</code>
 is created and assigned to stdin and stdout of
the child process, while stderr is inherited from the socat process, and the
child process uses file descriptors 0 and 1 for communicating with the main
socat process.
<dl>
<a name="OPTION_NOFORK"></a><dt><code>nofork</code><dd>
 Does not fork a subprocess for executing the program, instead calls execvp()
 or system() directly from the actual socat instance. This avoids the
 overhead of another process between the program and its peer,
 but introduces a lot of restrictions:
 <ul>
 <li> this option can only be applied to the second socat address.
 <li> it cannot be applied to a part of a <a href="socat.html#ADDRESS_DUAL">dual</a> address.
 <li> the first socat address cannot be OPENSSL or READLINE
 <li> socat options -b, -t, -D, -l, -v, -x become useless
 <li> for both addresses, options ignoreeof, cr, and crnl become useless
 <li> for the second address (the one with option nofork), options 
 append,  cloexec, flock, user, group, mode, nonblock,
 perm-late, setlk, and setpgid cannot be applied. Some of these could be
 used on the first address though.
 </ul>
<a name="OPTION_PIPES"></a><dt><code>pipes</code><dd>
 Creates a pair of unnamed pipes for interprocess communication instead of a
 socket pair.
<a name="OPTION_OPENPTY"></a><dt><code>openpty</code><dd>
 Establishes communication with the sub process using a pseudo terminal
 created with 
<code>openpty()</code>
 instead of the default (socketpair or ptmx).
<a name="OPTION_PTMX"></a><dt><code>ptmx</code><dd>
 Establishes communication with the sub process using a pseudo terminal
 created by opening /dev/ptmx or /dev/ptc instead of the default
 (socketpair).
<a name="OPTION_PTY"></a><dt><code>pty</code><dd>
 Establishes communication with the sub process using a pseudo terminal
 instead of a socket pair. Creates the pty with an available mechanism. If
 openpty and ptmx are both available, it uses ptmx because this is POSIX
 compliant (<a href="socat.html#EXAMPLE_OPTION_PTY">example</a>).
<a name="OPTION_CTTY"></a><dt><code>ctty</code><dd>
 Makes the pty the controlling tty of the sub process (<a href="socat.html#EXAMPLE_OPTION_CTTY">example</a>).
<a name="OPTION_STDERR"></a><dt><code>stderr</code><dd>
 Directs stderr of the sub process to its output channel by making stderr a
 
<code>dup()</code>
 of stdout (<a href="socat.html#EXAMPLE_OPTION_STDERR">example</a>). 
<a name="OPTION_FDIN"></a><dt><code>fdin=&lt;fdnum&gt;</code><dd>
 Assigns the sub processes input channel to its file descriptor
 <a href="socat.html#TYPE_FDNUM">&lt;fdnum&gt;</a> 
 instead of stdin (0). The program started from the subprocess has to use
 this fd for reading data from socat (<a href="socat.html#EXAMPLE_OPTION_FDIN">example</a>). 
<a name="OPTION_FDOUT"></a><dt><code>fdout=&lt;fdnum&gt;</code><dd>
 Assigns the sub processes output channel to its file descriptor
 <a href="socat.html#TYPE_FDNUM">&lt;fdnum&gt;</a> 
 instead of stdout (1). The program started from the subprocess has to use 
 this fd for writing data to socat (<a href="socat.html#EXAMPLE_OPTION_FDOUT">example</a>).
<a name="OPTION_SIGHUP"></a><a name="OPTION_SIGINT"></a><a name="OPTION_SIGQUIT"></a><dt><code>sighup</code>, <code>sigint</code>, <code>sigquit</code><dd>
 Has socat pass signals of this type to the sub process.
 If no address has this option, socat terminates on these signals.
</dl>

<dl></dl> 

<a name="GROUP_TERMIOS"></a>TERMIOS option group

For addresses that work on a tty (e.g., stdio, file:/dev/tty, exec:...,pty), the terminal parameters defined in the UN*X termios mechanism are made available as address option parameters.
Please note that changes of the parameters of your interactive terminal 
remain effective after socat's termination, so you might have to enter "reset"
or "stty sane" in your shell afterwards.
For EXEC and SYSTEM addresses with option PTY,
these options apply to the pty by the child processes.

<dl>
<a name="OPTION_B0"></a><dt><code>b0</code><dd>
 Disconnects the terminal.
<a name="OPTION_B19200"></a><dt><code>b19200</code><dd>
 Sets the serial line speed to 19200 baud. Some other rates are possible; use
something like <code>socat -hh |grep ' b[1-9]'</code> to find all speeds supported by
your implementation. 
Note: On some operating systems, these options may not be
available. Use <a href="socat.html#OPTION_ISPEED">ispeed</a> or <a href="socat.html#OPTION_OSPEED">ospeed</a>
instead.
<a name="OPTION_ECHO"></a><dt><code>echo=&lt;bool&gt;</code><dd>
 Enables or disables local echo.
<a name="OPTION_ICANON"></a><dt><code>icanon=&lt;bool&gt;</code><dd>
 Sets or clears canonical mode, enabling line buffering and some special
 characters. 
<a name="OPTION_RAW"></a><dt><code>raw</code><dd>
 Sets raw mode, thus passing input and output almost unprocessed. This option is obsolete, use option <a href="socat.html#OPTION_TERMIOS_RAWER">rawer</a> or <a href="socat.html#OPTION_TERMIOS_CFMAKERAW">cfmakeraw</a> instead.
<a name="OPTION_TERMIOS_RAWER"></a><dt><code>rawer</code><dd>
 Makes terminal rawer than <a href="socat.html#OPTION_RAW">raw</a> option. This option implicitly turns off echo. (<a href="socat.html#EXAMPLE_OPTION_TERMIOS_RAWER">example</a>).
<a name="OPTION_TERMIOS_CFMAKERAW"></a><dt><code>cfmakeraw</code><dd>
 Sets raw mode by invoking <code>cfmakeraw()</code> or by simulating this call. This option implicitly turns off echo.
<a name="OPTION_IGNBRK"></a><dt><code>ignbrk=&lt;bool&gt;</code><dd>
 Ignores or interpretes the BREAK character (e.g., ^C)
<a name="OPTION_BRKINT"></a><dt><code>brkint=&lt;bool&gt;</code><dd>
<a name="OPTION_BS0"></a><dt><code>bs0</code><dd>
<a name="OPTION_BS1"></a><dt><code>bs1</code><dd>
<a name="OPTION_BSDLY"></a><dt><code>bsdly=&lt;0|1&gt;</code><dd>
<a name="OPTION_CLOCAL"></a><dt><code>clocal=&lt;bool&gt;</code><dd>

<a name="OPTION_CR0"></a><a name="OPTION_CR1"></a><a name="OPTION_CR2"></a><a name="OPTION_CR3"></a>

<dt><code>cr0 
cr1 
cr2 
cr3</code><dd>
 Sets the carriage return delay to 0, 1, 2, or 3, respectively.
 0 means no delay, the other values are terminal dependent.

<a name="OPTION_CRDLY"></a><dt><code>crdly=&lt;0|1|2|3&gt;</code><dd>
<a name="OPTION_CREAD"></a><dt><code>cread=&lt;bool&gt;</code><dd>
<a name="OPTION_CRTSCTS"></a><dt><code>crtscts=&lt;bool&gt;</code><dd>

<a name="OPTION_CS5"></a><a name="OPTION_CS6"></a><a name="OPTION_CS7"></a><a name="OPTION_CS8"></a>

<dt><code>cs5 
cs6 
cs7 
cs8</code><dd>
 Sets the character size to 5, 6, 7, or 8 bits, respectively.

<a name="OPTION_CSIZE"></a><dt><code>csize=&lt;0|1|2|3&gt;</code><dd>
<a name="OPTION_CSTOPB"></a><dt><code>cstopb=&lt;bool&gt;</code><dd>
 Sets two stop bits, rather than one.
<a name="OPTION_VDSUSP"></a><dt><code>dsusp=&lt;byte&gt;</code><dd>
 Sets the value for the VDSUSP character that suspends the current foreground
 process and reactivates the shell (all except Linux).
<a name="OPTION_ECHOCTL"></a><dt><code>echoctl=&lt;bool&gt;</code><dd>
 Echos control characters in hat notation (e.g. ^A)
<a name="OPTION_ECHOE"></a><dt><code>echoe=&lt;bool&gt;</code><dd>
<a name="OPTION_ECHOK"></a><dt><code>echok=&lt;bool&gt;</code><dd>
<a name="OPTION_ECHOKE"></a><dt><code>echoke=&lt;bool&gt;</code><dd>
<a name="OPTION_ECHONL"></a><dt><code>echonl=&lt;bool&gt;</code><dd>
<a name="OPTION_ECHOPRT"></a><dt><code>echoprt=&lt;bool&gt;</code><dd>
<a name="OPTION_EOF"></a><dt><code>eof=&lt;byte&gt;</code><dd>
<a name="OPTION_EOL"></a><dt><code>eol=&lt;byte&gt;</code><dd>
<a name="OPTION_EOL2"></a><dt><code>eol2=&lt;byte&gt;</code><dd>
<a name="OPTION_ERASE"></a><dt><code>erase=&lt;byte&gt;</code><dd>
<a name="OPTION_DISCARD"></a><dt><code>discard=&lt;byte&gt;</code><dd>
<a name="OPTION_FF0"></a><dt><code>ff0</code><dd>
<a name="OPTION_FF1"></a><dt><code>ff1</code><dd>
<a name="OPTION_FFDLY"></a><dt><code>ffdly=&lt;bool&gt;</code><dd>
<a name="OPTION_FLUSHO"></a><dt><code>flusho=&lt;bool&gt;</code><dd>
<a name="OPTION_HUPCL"></a><dt><code>hupcl=&lt;bool&gt;</code><dd>
<a name="OPTION_ICRNL"></a><dt><code>icrnl=&lt;bool&gt;</code><dd>
<a name="OPTION_IEXTEN"></a><dt><code>iexten=&lt;bool&gt;</code><dd>
<a name="OPTION_IGNCR"></a><dt><code>igncr=&lt;bool&gt;</code><dd>
<a name="OPTION_IGNPAR"></a><dt><code>ignpar=&lt;bool&gt;</code><dd>
<a name="OPTION_IMAXBEL"></a><dt><code>imaxbel=&lt;bool&gt;</code><dd>
<a name="OPTION_INLCR"></a><dt><code>inlcr=&lt;bool&gt;</code><dd>
<a name="OPTION_INPCK"></a><dt><code>inpck=&lt;bool&gt;</code><dd>
<a name="OPTION_INTR"></a><dt><code>intr=&lt;byte&gt;</code><dd>
<a name="OPTION_ISIG"></a><dt><code>isig=&lt;bool&gt;</code><dd>
<a name="OPTION_ISPEED"></a><dt><code>ispeed=&lt;unsigned-int&gt;</code><dd>
 Set the baud rate for incoming data on this line. 
 See also: <a href="socat.html#OPTION_OSPEED">ospeed</a>, <a href="socat.html#OPTION_B19200">b19200</a>
<a name="OPTION_ISTRIP"></a><dt><code>istrip=&lt;bool&gt;</code><dd>
<a name="OPTION_IUCLC"></a><dt><code>iuclc=&lt;bool&gt;</code><dd>
<a name="OPTION_IXANY"></a><dt><code>ixany=&lt;bool&gt;</code><dd>
<a name="OPTION_IXOFF"></a><dt><code>ixoff=&lt;bool&gt;</code><dd>
<a name="OPTION_IXON"></a><dt><code>ixon=&lt;bool&gt;</code><dd>
<a name="OPTION_KILL"></a><dt><code>kill=&lt;byte&gt;</code><dd>
<a name="OPTION_LNEXT"></a><dt><code>lnext=&lt;byte&gt;</code><dd>
<a name="OPTION_MIN"></a><dt><code>min=&lt;byte&gt;</code><dd>
<a name="OPTION_NL0"></a><dt><code>nl0</code><dd>
 Sets the newline delay to 0.
<a name="OPTION_NL1"></a><dt><code>nl1</code><dd>
<a name="OPTION_NLDLY"></a><dt><code>nldly=&lt;bool&gt;</code><dd>
<a name="OPTION_NOFLSH"></a><dt><code>noflsh=&lt;bool&gt;</code><dd>
<a name="OPTION_OCRNL"></a><dt><code>ocrnl=&lt;bool&gt;</code><dd>
<a name="OPTION_OFDEL"></a><dt><code>ofdel=&lt;bool&gt;</code><dd>
<a name="OPTION_OFILL"></a><dt><code>ofill=&lt;bool&gt;</code><dd>
<a name="OPTION_OLCUC"></a><dt><code>olcuc=&lt;bool&gt;</code><dd>
<a name="OPTION_ONLCR"></a><dt><code>onlcr=&lt;bool&gt;</code><dd>
<a name="OPTION_ONLRET"></a><dt><code>onlret=&lt;bool&gt;</code><dd>
<a name="OPTION_ONOCR"></a><dt><code>onocr=&lt;bool&gt;</code><dd>
<a name="OPTION_OPOST"></a><dt><code>opost=&lt;bool&gt;</code><dd>
 Enables or disables output processing; e.g., converts NL to CR-NL.
<a name="OPTION_OSPEED"></a><dt><code>ospeed=&lt;unsigned-int&gt;</code><dd>
 Set the baud rate for outgoing data on this line. 
 See also: <a href="socat.html#OPTION_ISPEED">ispeed</a>, <a href="socat.html#OPTION_B19200">b19200</a>
<a name="OPTION_PARENB"></a><dt><code>parenb=&lt;bool&gt;</code><dd>
 Enable parity generation on output and parity checking for input.
<a name="OPTION_PARMRK"></a><dt><code>parmrk=&lt;bool&gt;</code><dd>
<a name="OPTION_PARODD"></a><dt><code>parodd=&lt;bool&gt;</code><dd>
<a name="OPTION_PENDIN"></a><dt><code>pendin=&lt;bool&gt;</code><dd>
<a name="OPTION_QUIT"></a><dt><code>quit=&lt;byte&gt;</code><dd>
<a name="OPTION_REPRINT"></a><dt><code>reprint=&lt;byte&gt;</code><dd>
<a name="OPTION_SANE"></a><dt><code>sane</code><dd>
 Brings the terminal to something like a useful default state.
<a name="OPTION_START"></a><dt><code>start=&lt;byte&gt;</code><dd>
<a name="OPTION_STOP"></a><dt><code>stop=&lt;byte&gt;</code><dd>
<a name="OPTION_SUSP"></a><dt><code>susp=&lt;byte&gt;</code><dd>
<a name="OPTION_SWTC"></a><dt><code>swtc=&lt;byte&gt;</code><dd>
<a name="OPTION_TAB0"></a><dt><code>tab0</code><dd>
<a name="OPTION_TAB1"></a><dt><code>tab1</code><dd>
<a name="OPTION_TAB2"></a><dt><code>tab2</code><dd>
<a name="OPTION_TAB3"></a><dt><code>tab3</code><dd>
<a name="OPTION_TABDLY"></a><dt><code>tabdly=&lt;unsigned-int&gt;</code><dd>
<a name="OPTION_TIME"></a><dt><code>time=&lt;byte&gt;</code><dd>
<a name="OPTION_TOSTOP"></a><dt><code>tostop=&lt;bool&gt;</code><dd>
<a name="OPTION_VT0"></a><dt><code>vt0</code><dd>
<a name="OPTION_VT1"></a><dt><code>vt1</code><dd>
<a name="OPTION_VTDLY"></a><dt><code>vtdly=&lt;bool&gt;</code><dd>
<a name="OPTION_WERASE"></a><dt><code>werase=&lt;byte&gt;</code><dd>
<a name="OPTION_XCASE"></a><dt><code>xcase=&lt;bool&gt;</code><dd>
<a name="OPTION_XTABS"></a><dt><code>xtabs</code><dd>
<a name="OPTION_I_POP_ALL"></a><dt><code>i-pop-all</code><dd>
 With UNIX System V STREAMS, removes all drivers from the stack.
<a name="OPTION_I_PUSH"></a><dt><code>i-push=&lt;string&gt;</code><dd>
 With UNIX System V STREAMS, pushes the driver (module) with the given name
 (<a href="socat.html#TYPE_STRING">string</a>) onto the stack. For example, to make sure that a
 character device on Solaris supports termios etc, use the following options:
 <code>i-pop-all,i-push=ptem,i-push=ldterm,i-push=ttcompat</code>
</dl>

<dl></dl> 

<a name="GROUP_PTY"></a>PTY option group

These options are intended for use with the <a href="socat.html#ADDRESS_PTY">pty</a> address
type.

<dl>
<a name="OPTION_SYMBOLIC_LINK"></a><dt><code>link=&lt;filename&gt;</code><dd>
 Generates a symbolic link that points to the actual pseudo terminal
 (pty). This might help 
 to solve the problem that ptys are generated with more or less
 unpredictable names, making it difficult to directly access the socat
 generated pty automatically. With this option, the user can specify a "fix"
 point in the file hierarchy that helps him to access the actual pty
 (<a href="socat.html#EXAMPLE_OPTION_SYMBOLIC_LINK">example</a>).
 Beginning with socat version 1.4.3, the symbolic link is removed when
 the address is closed (but see option <a href="socat.html#OPTION_UNLINK_CLOSE">unlink-close</a>).
<a name="OPTION_PTY_WAIT_SLAVE"></a><dt><code>wait-slave</code><dd>
 Blocks the open phase until a process opens the slave side of the pty.
 Usually, socat continues after generating the pty with opening the next
 address or with entering the transfer loop. With the wait-slave option,
 socat waits until some process opens the slave side of the pty before
 continuing. 
 This option only works if the operating system provides the <code>poll()</code>
 system call. And it depends on an undocumented behaviour of pty's, so it
 does not work on all operating systems. It has successfully been tested on
 Linux, FreeBSD, NetBSD, and on Tru64 with openpty. 
<a name="OPTION_PTY_INTERVAL"></a><dt><code>pty-interval=&lt;seconds&gt;</code><dd>
 When the <a href="socat.html#OPTION_PTY_WAIT_SLAVE">wait-slave</a> option is set, socat
 periodically checks the HUP condition using <code>poll()</code> to find if the pty's
 slave side has been opened. The default polling interval is 1s. Use the
 pty-interval option [<a href="socat.html#TYPE_TIMEVAL">timeval</a>] to change this value.
</dl>

<dl></dl> 

<a name="GROUP_OPENSSL"></a>OPENSSL option group

These options apply to the <a href="socat.html#ADDRESS_OPENSSL_CONNECT">openssl</a> and
<a href="socat.html#ADDRESS_OPENSSL_LISTEN">openssl-listen</a> address types.

<dl>
<a name="OPTION_OPENSSL_CIPHERLIST"></a><dt><code>cipher=&lt;cipherlist&gt;</code><dd>
 Selects the list of ciphers that may be used for the connection.
 See the man page of 
<code>ciphers</code>
, section CIPHER LIST FORMAT, for
 detailed information about syntax, values, and default of &lt;cipherlist&gt;. 
 Several cipher strings may be given, separated by ':'.
 Some simple cipher strings:
 <dl>
 <dt>3DES<dd> Uses a cipher suite with triple DES.
 <dt>MD5<dd> Uses a cipher suite with MD5.
 <dt>aNULL<dd> Uses a cipher suite without authentication.
 <dt>NULL<dd> Does not use encryption.
 <dt>HIGH<dd> Uses a cipher suite with "high" encryption.
 </dl>
 Note that the peer must support the selected property, or the negotiation
 will fail.
<a name="OPTION_OPENSSL_METHOD"></a><dt><code>method=&lt;ssl-method&gt;</code><dd>
 This option is based on deprecated functions and is only available when
 socat was build with option <code>--with-openssl-method</code>.
 Sets the protocol version to be used. Valid strings (not case sensitive)
 are: 
 <dl>
 <dt><code>SSL2</code><dd> Select SSL protocol version 2.
 <dt><code>SSL3</code><dd> Select SSL protocol version 3.
 <dt><code>SSL23</code><dd> Select the best available SSL or TLS protocol.
 <dt><code>TLS1</code><dd> Select TLS protocol version 1.
 <dt><code>TLS1.1</code><dd> Select TLS protocol version 1.1.
 <dt><code>TLS1.2</code><dd> Select TLS protocol version 1.2.
 When this option is not provided OpenSSL negotiates the mothod with its
 peer.
 </dl>
<a name="OPTION_OPENSSL_VERIFY"></a><dt><code>verify=&lt;bool&gt;</code><dd>
 Controls check of the peer's certificate. Default is 1 (true). Disabling
 verify might open your socket for everyone, making the encryption useless!
<a name="OPTION_OPENSSL_CERTIFICATE"></a><dt><code>cert=&lt;filename&gt;</code><dd>
 Specifies the file with the certificate and private key for authentication. 
 The certificate must be in OpenSSL format (*.pem). 
 With openssl-listen, use of this option is strongly
 recommended. Except with cipher aNULL, "no shared ciphers" error will
 occur when no certificate is given.
<a name="OPTION_OPENSSL_KEY"></a><dt><code>key=&lt;filename&gt;</code><dd>
 Specifies the file with the private key. The private key may be in this
 file or in the file given with the <a href="socat.html#OPTION_OPENSSL_CERTIFICATE">cert</a> option. The party that has
 to proof that it is the owner of a certificate needs the private key.
<a name="OPTION_OPENSSL_DHPARAMS"></a><dt><code>dhparams=&lt;filename&gt;</code><dd>
 Specifies the file with the Diffie Hellman parameters. These parameters may
 also be in the file given with the <a href="socat.html#OPTION_OPENSSL_CERTIFICATE">cert</a>
 option in which case the dhparams option is not needed.
<a name="OPTION_OPENSSL_CAFILE"></a><dt><code>cafile=&lt;filename&gt;</code><dd>
 Specifies the file with the trusted (root) authority certificates. The file
 must be in PEM format and should contain one or more certificates. The party
 that checks the authentication of its peer trusts only certificates that are
 in this file.
<a name="OPTION_OPENSSL_CAPATH"></a><dt><code>capath=&lt;dirname&gt;</code><dd>
 Specifies the directory with the trusted (root) certificates. The directory
 must contain certificates in PEM format and their hashes (see OpenSSL
 documentation) 
<a name="OPTION_OPENSSL_EGD"></a><dt><code>egd=&lt;filename&gt;</code><dd>
 On some systems, openssl requires an explicit source of random data. Specify
 the socket name where an entropy gathering daemon like egd provides random
 data, e.g. /dev/egd-pool.
<a name="OPTION_OPENSSL_PSEUDO"></a><dt><code>pseudo</code><dd>
 On systems where openssl cannot find an entropy source and where no entropy
 gathering daemon can be utilized, this option activates a mechanism for
 providing pseudo entropy. This is achieved by taking the current time in
 microseconds for feeding the libc pseudo random number generator with an
 initial value. openssl is then feeded with output from random() calls. 
 NOTE:This mechanism is not sufficient for generation of secure keys!
<a name="OPTION_OPENSSL_COMPRESS"></a><dt><code>compress</code><dd>
 Enable or disable the use of compression for a connection. Setting this to
 "none" disables compression, setting it to "auto" lets OpenSSL choose the best
 available algorithm supported by both parties. The default is to not touch any
 compression-related settings.
 NOTE: Requires OpenSSL 0.9.8 or higher and disabling compression with
 OpenSSL 0.9.8 affects all new connections in the process.
<a name="OPTION_OPENSSL_COMMONNAME"></a><dt><code>commonname=&lt;string&gt;</code><dd>
 Specify the commonname that the peer certificate must match. With
 <a href="socat.html#ADDRESS_OPENSSL_CONNECT">OPENSSL-CONNECT</a> address this overrides the
 given hostname or IP target address; with
 <a href="socat.html#ADDRESS_OPENSSL_LISTEN">OPENSSL-LISTEN</a> this turns on check of peer
 certificates commonname. This option has only meaning when option
 <a href="socat.html#OPTION_OPENSSL_VERIFY">verify</a> is not disabled and the chosen cipher
 provides a peer certificate.
<a name="OPTION_OPENSSL_NO_SNI"></a><dt><code>no-sni=&lt;bool&gt;</code><dd>
 Do not use the client side Server Name Indication (SNI) feature that selects
 the desired server certificate. 
 Note: SNI is automatically used since socat version 1.7.4.0 and uses
 <a href="socat.html#OPTION_OPENSSL_COMMONNAME">commonname</a> or the given host name.
<a name="OPTION_OPENSSL_SNIHOST"></a><dt><code>snihost=&lt;string&gt;</code><dd>
 Set the client side Server Name Indication (SNI) host name different from
 the addressed server name or common name. This might be useful when the
 server certificate has multiple host names or wildcard names because the
 SNI host name is passed in cleartext to the server and might be eavesdropped;
 with this option a mock name of the desired certificate may be transferred.
<a name="OPTION_OPENSSL_FIPS"></a><dt><code>fips</code><dd>
 Enables FIPS mode if compiled in. For info about the FIPS encryption
 implementation standard see <a href="http://oss-institute.org/fips-faq.html">http://oss-institute.org/fips-faq.html</a>. 
 This mode might require that the involved certificates are generated with a
 FIPS enabled version of openssl. Setting or clearing this option on one
 socat address affects all OpenSSL addresses of this process.
</dl>

<dl></dl> 

<a name="GROUP_RETRY"></a>RETRY option group

Options that control retry of some system calls, especially connection
attempts.

<dl>
<a name="OPTION_RETRY"></a><dt><code>retry=&lt;num&gt;</code><dd>
 Number of retries before the connection or listen attempt is aborted. 
 Default is 0, which means just one attempt. 
<a name="OPTION_INTERVAL"></a><dt><code>interval=&lt;timespec&gt;</code><dd>
 Time between consecutive attempts (seconds, 
 [<a href="socat.html#TYPE_TIMESPEC">timespec</a>]). Default is 1 second.
<a name="OPTION_FOREVER"></a><dt><code>forever</code><dd>
 Performs an unlimited number of retry attempts.
</dl>

<dl></dl> 

<a name="GROUP_TUN"></a>TUN option group

Options that control Linux TUN/TAP interface device addresses.

<dl>
<a name="OPTION_TUN_DEVICE"></a><dt><code>tun-device=&lt;device-file&gt;</code><dd>
 Instructs socat to take another path for the TUN clone device. Default is
 <code>/dev/net/tun</code>.
<a name="OPTION_TUN_NAME"></a><dt><code>tun-name=&lt;if-name&gt;</code><dd>
 Gives the resulting network interface a specific name instead of the system
 generated (tun0, tun1, etc.)
<a name="OPTION_TUN_TYPE"></a><dt><code>tun-type=[tun|tap]</code><dd>
 Sets the type of the TUN device; use this option to generate a TAP
 device. See the Linux docu for the difference between these types.
 When you try to establish a tunnel between two TUN devices, their types
 should be the same.
<a name="OPTION_IFF_NO_PI"></a><dt><code>iff-no-pi</code><dd>
 Sets the IFF_NO_PI flag which controls if the device includes additional
 packet information in the tunnel.
 When you try to establish a tunnel between two TUN devices, these flags
 should have the same values.
<a name="OPTION_IFF_UP"></a><dt><code>iff-up</code><dd>
 Sets the TUN network interface status UP. Strongly recommended.
<a name="OPTION_IFF_BROADCAST"></a><dt><code>iff-broadcast</code><dd>
 Sets the BROADCAST flag of the TUN network interface.
<a name="OPTION_IFF_DEBUG"></a><dt><code>iff-debug</code><dd>
 Sets the DEBUG flag of the TUN network interface.
<a name="OPTION_IFF_LOOPBACK"></a><dt><code>iff-loopback</code><dd>
 Sets the LOOPBACK flag of the TUN network interface.
<a name="OPTION_IFF_POINTOPOINT"></a><dt><code>iff-pointopoint</code><dd>
 Sets the POINTOPOINT flag of the TUN device.
<a name="OPTION_IFF_NOTRAILERS"></a><dt><code>iff-notrailers</code><dd>
 Sets the NOTRAILERS flag of the TUN device.
<a name="OPTION_IFF_RUNNING"></a><dt><code>iff-running</code><dd>
 Sets the RUNNING flag of the TUN device.
<a name="OPTION_IFF_NOARP"></a><dt><code>iff-noarp</code><dd>
 Sets the NOARP flag of the TUN device.
<a name="OPTION_IFF_PROMISC"></a><dt><code>iff-promisc</code><dd>
 Sets the PROMISC flag of the TUN device.
<a name="OPTION_IFF_ALLMULTI"></a><dt><code>iff-allmulti</code><dd>
 Sets the ALLMULTI flag of the TUN device.
<a name="OPTION_IFF_MASTER"></a><dt><code>iff-master</code><dd>
 Sets the MASTER flag of the TUN device.
<a name="OPTION_IFF_SLAVE"></a><dt><code>iff-slave</code><dd>
 Sets the SLAVE flag of the TUN device.
<a name="OPTION_IFF_MULTICAST"></a><dt><code>iff-multicast</code><dd>
 Sets the MULTICAST flag of the TUN device.
<a name="OPTION_IFFPORTSEL_"></a><dt><code>iff-portsel</code><dd>
 Sets the PORTSEL flag of the TUN device.
<a name="OPTION_IFF_AUTOMEDIA"></a><dt><code>iff-automedia</code><dd>
 Sets the AUTOMEDIA flag of the TUN device.
<a name="OPTION_IFF_DYNAMIC"></a><dt><code>iff-dynamic</code><dd>
 Sets the DYNAMIC flag of the TUN device.
</dl>

<dl></dl> 

<a name="VALUES"></a>
<h2>DATA VALUES</h2>

This section explains the different data types that address parameters and
address options can take.

<dl>
<a name="TYPE_ADDRESS_RANGE"></a><dt>address-range<dd>
 Is currently only implemented for IPv4 and IPv6. See address-option
 <a href="socat.html#OPTION_RANGE">`range'</a> 
<a name="TYPE_BOOL"></a><dt>bool<dd>
 "0" or "1"; if value is omitted, "1" is taken.
<a name="TYPE_BYTE"></a><dt>byte<dd>
 An unsigned int number, read with 
<code>strtoul()</code>
, lower or equal to
 
<code>UCHAR_MAX</code>
.
<a name="TYPE_COMMAND_LINE"></a><dt>command-line<dd>
 A string specifying a program name and its arguments, separated by single
 spaces. 
<a name="TYPE_DATA"></a><dt>data<dd>
 This is a more general data specification. The given text string contains
 information about the target data type and value. Generally a leading
 character specifies the type of the following data item. In its specific
 context a default data type may exist. 
 Currently only the following specifications are implemented: 
 <dl>
 <dt>i<dd> A signed integer number, stored in host byte order. 
 Example: i-1000 (Integer number -1000)
 <dt>I<dd> An unsigned integer number, stored in host byte order. 
 <dt>l<dd> A signed long integer number, stored in host byte order. 
 <dt>L<dd> An unsigned long integer number, stored in host byte order. 
 <dt>s<dd> A signed short integer number, stored in host byte order. 
 <dt>S<dd> An unsigned short integer number, stored in host byte order. 
 <dt>b<dd> A signed byte (signed char). 
 <dt>B<dd> An unsigned byte (unsigned char). 
 <dt>x<dd> Following is an even number of hex digits, stored as sequence of
 bytes. 
 Example: x7f000001 (IP address 127.0.0.1)
 <dt>"<dd> Following is a string that is used with the common conversions 
 \n \r \t \f \b \a \e \0; the string must be closed with '"'. Please note
 that the quotes and backslashes need to be escaped from shell and socat
 conversion. 
 Example: "Hello world!\n"
 <dt>'<dd> A single char, with the usual conversions. Please note that the
 quotes and backslashes need to be escaped from shell and socat conversion.
 
 Example: 'a'
 </dl>
 Data items may be separated with white space without need to repeat the type
 specifier again.
<a name="TYPE_DIRECTORY"></a><dt>directory<dd>
 A string with usual UN*X directory name semantics.
<a name="TYPE_FACILITY"></a><dt>facility<dd>
 The name of a syslog facility in lower case characters.
<a name="TYPE_FDNUM"></a><dt>fdnum<dd>
 An unsigned int type, read with 
<code>strtoul()</code>
, specifying a UN*X file
 descriptor. 
<a name="TYPE_FILENAME"></a><dt>filename<dd>
 A string with usual UN*X filename semantics.
<a name="TYPE_GROUP"></a><dt>group<dd>
 If the first character is a decimal digit, the value is read with
 
<code>strtoul()</code>
 as unsigned integer specifying a group id. Otherwise, it
 must be an existing group name.
<a name="TYPE_INT"></a><dt>int<dd>
 A number following the rules of the 
<code>strtol()</code>
 function with base
 "0", i.e. decimal number, octal number with leading "0", or hexadecimal
 number with leading "0x". The value must fit into a C int.
<a name="TYPE_INTERFACE"></a><dt>interface<dd>
 A string specifying the device name of a network interface
 as shown by ifconfig or procan, e.g. "eth0".
<a name="TYPE_IP_ADDRESS"></a><dt>IP address<dd>
 An IPv4 address in numbers-and-dots notation, an IPv6 address in hex
 notation enclosed in brackets, or a hostname that resolves to an IPv4 or an
 IPv6 address. 
 Examples: 127.0.0.1, [::1], www.dest-unreach.org, dns1
<a name="TYPE_IPV4_ADDRESS"></a><dt>IPv4 address<dd>
 An IPv4 address in numbers-and-dots notation or a hostname that resolves to
 an IPv4 address. 
 Examples: 127.0.0.1, www.dest-unreach.org, dns2
<a name="TYPE_IPV6_ADDRESS"></a><dt>IPv6 address<dd>
 An IPv6 address in hexnumbers-and-colons notation enclosed in brackets, or a
 hostname that resolves to an IPv6 address. 
 Examples: [::1], [1234:5678:9abc:def0:1234:5678:9abc:def0],
 ip6name.domain.org 
<a name="TYPE_LONG"></a><dt>long<dd>
 A number read with 
<code>strtol()</code>
. The value must fit into a C long.
<a name="TYPE_LONGLONG"></a><dt>long long<dd>
 A number read with 
<code>strtoll()</code>
. The value must fit into a C long long.
<a name="TYPE_OFF"></a><dt>off_t<dd>
 An implementation dependend signed number, usually 32 bits, read with strtol
 or strtoll.
<a name="TYPE_OFF64"></a><dt>off64_t<dd>
 An implementation dependend signed number, usually 64 bits, read with strtol
 or strtoll.
<a name="TYPE_MODE_T"></a><dt>mode_t<dd>
 An unsigned integer, read with 
<code>strtoul()</code>
, specifying mode (permission)
 bits. 
<a name="TYPE_PID_T"></a><dt>pid_t<dd>
 A number, read with 
<code>strtol()</code>
, specifying a process id.
<a name="TYPE_PORT"></a><dt>port<dd>
 A uint16_t (16 bit unsigned number) specifying a TCP or UDP port, read
 with 
<code>strtoul()</code>
.
<a name="TYPE_PROTOCOL"></a><dt>protocol<dd>
 An unsigned 8 bit number, read with 
<code>strtoul()</code>
.
<a name="TYPE_SIZE_T"></a><dt>size_t<dd>
 An unsigned number with size_t limitations, read with 
<code>strtoul</code>
.
<a name="TYPE_SOCKNAME"></a><dt>sockname<dd>
 A socket address. See address-option <a href="socat.html#OPTION_BIND">`bind'</a>
<a name="TYPE_STRING"></a><dt>string<dd>
 A sequence of characters, not containing '\0' and, depending on
 the position within the command line, ':', ',', or "!!". Note
 that you might have to escape shell meta characters in the command line.
<a name="TYPE_TCP_SERVICE"></a><dt>TCP service<dd>
 A service name, not starting with a digit, that is resolved by
 
<code>getservbyname()</code>
, or an unsigned int 16 bit number read with
 
<code>strtoul()</code>
.
<a name="TYPE_TIMEVAL"></a><dt>timeval<dd>
 A double float specifying seconds; the number is mapped into a
 struct timeval, consisting of seconds and microseconds.
<a name="TYPE_TIMESPEC"></a><dt>timespec<dd>
 A double float specifying seconds; the number is mapped into a
 struct timespec, consisting of seconds and nanoseconds.
<a name="TYPE_UDP_SERVICE"></a><dt>UDP service<dd>
 A service name, not starting with a digit, that is resolved by
 
<code>getservbyname()</code>
, or an unsigned int 16 bit number read with
 
<code>strtoul()</code>
.
<a name="TYPE_UNSIGNED_INT"></a><dt>unsigned int<dd>
 A number read with 
<code>strtoul()</code>
. The value must fit into a C unsigned
 int. 
<a name="TYPE_USER"></a><dt>user<dd>
 If the first character is a decimal digit, the value is read with
 
<code>strtoul()</code>
 as unsigned integer specifying a user id. Otherwise, it must
 be an existing user name.
<a name="TYPE_VSOCK_ADDRESS"></a><dt>VSOCK cid<dd>
 A uint32_t (32 bit unsigned number) specifying a VSOCK Context Identifier
 (CID), read with 
<code>strtoul()</code>
.
 There are several special addresses: VMADDR_CID_ANY (-1U) means any address
 for binding; VMADDR_CID_HOST (2) is the well-known address of the host.
<a name="TYPE_VSOCK_PORT"></a><dt>VSOCK port<dd>
 A uint32_t (32 bit unsigned number) specifying a VSOCK port, read
 with 
<code>strtoul()</code>
.
</dl>

<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>

<dl>

<a name="EXAMPLE_ADDRESS_TCP4_CONNECT"></a>
<dt><code>socat - TCP4:www.domain.org:80</code><dd>

transfers data between <a href="socat.html#ADDRESS_STDIO">STDIO</a> (-) and a
<a href="socat.html#ADDRESS_TCP4_CONNECT">TCP4</a> connection to port 80 of host 
www.domain.org. This example results in an interactive connection similar to
telnet or netcat. The stdin terminal parameters are not changed, so you may
close the relay with ^D or abort it with ^C.

<a name="EXAMPLE_ADDRESS_READLINE"></a>
<a name="EXAMPLE_OPTION_HISTORY"></a>

<dt><code>socat -d -d READLINE,history=$HOME/.http_history \ 
TCP4:www.domain.org:www,crnl</code><dd>

this is similar to the previous example, but you can edit the current line in a
bash like manner (<a href="socat.html#ADDRESS_READLINE">READLINE</a>) and use the
<a href="socat.html#OPTION_HISTORY">history</a> file .http_history; socat prints messages about
progress (<a href="socat.html#option_d_d">-d -d</a>). The port is specified by service name
(www), and correct network line termination characters
(<a href="socat.html#OPTION_CRNL">crnl</a>) instead of NL are used.

<a name="EXAMPLE_ADDRESS_TCP4_LISTEN"></a>
<dt><code>socat TCP4-LISTEN:www TCP4:www.domain.org:www</code><dd>

installs a simple TCP port forwarder. With
<a href="socat.html#ADDRESS_TCP4_LISTEN">TCP4-LISTEN</a> it listens on local port "www" until a
connection comes in, accepts it, then connects to the remote host
(<a href="socat.html#ADDRESS_TCP4_CONNECT">TCP4</a>) and starts data transfer. It will not accept
a second connection. 

<a name="EXAMPLE_OPTION_BIND_TCP4"></a>
<a name="EXAMPLE_OPTION_REUSEADDR"></a>
<a name="EXAMPLE_OPTION_FORK"></a>
<a name="EXAMPLE_OPTION_SUBSTUSER"></a>
<a name="EXAMPLE_OPTION_RANGE"></a>

<dt><code>socat -d -d -lmlocal2 \ 
TCP4-LISTEN:80,bind=myaddr1,su=nobody,fork,range=10.0.0.0/8,reuseaddr \ 
TCP4:www.domain.org:80,bind=myaddr2</code><dd>

TCP port forwarder, each side bound to another local IP address
(<a href="socat.html#OPTION_BIND">bind</a>). This example handles an almost
arbitrary number of parallel or consecutive connections by
<a href="socat.html#OPTION_FORK">fork</a>'ing a new 
process after each 
<code>accept()</code>
. It provides a little security by
<a href="socat.html#OPTION_SUBSTUSER">su</a>'ing to user 
nobody after forking; it only permits connections from the private 10 network
(<a href="socat.html#OPTION_RANGE">range</a>); due to <a href="socat.html#OPTION_REUSEADDR">reuseaddr</a>, it
allows immediate restart after master process's termination, even if some child
sockets are not completely shut down.
With <a href="socat.html#option_lm">-lmlocal2</a>, socat logs to stderr until successfully
reaching the accept loop. Further logging is directed to syslog with facility
local2.

<a name="EXAMPLE_ADDRESS_EXEC"></a>
<a name="EXAMPLE_OPTION_TCPWRAPPERS"></a>
<a name="EXAMPLE_OPTION_CHROOT"></a>
<a name="EXAMPLE_OPTION_SUBSTUSER_DELAYED"></a>
<a name="EXAMPLE_OPTION_PTY"></a>
<a name="EXAMPLE_OPTION_STDERR"></a>

<dt><code>socat TCP4-LISTEN:5555,fork,tcpwrap=script \ 
EXEC:/bin/myscript,chroot=/home/sandbox,su-d=sandbox,pty,stderr</code><dd>

a simple server that accepts connections
(<a href="socat.html#ADDRESS_TCP4_LISTEN">TCP4-LISTEN</a>) and <a href="socat.html#OPTION_FORK">fork</a>'s a new
child process for each connection; every child acts as single relay. 
The client must match the rules for daemon process name "script" in
/etc/hosts.allow and /etc/hosts.deny, otherwise it is refused access (see "man
5 hosts_access").
For <a href="socat.html#ADDRESS_EXEC">EXEC</a>'uting the program, the child process
<a href="socat.html#OPTION_CHROOT">chroot</a>'s 
to /home/sandbox, <a href="socat.html#OPTION_SUBSTUSER">su</a>'s to user sandbox, and then starts 
the program /home/sandbox/bin/myscript. Socat and
myscript communicate via a pseudo tty (<a href="socat.html#OPTION_PTY">pty</a>); myscript's
<a href="socat.html#OPTION_STDERR">stderr</a> is redirected to stdout,
so its error messages are transferred via socat to the connected client. 

<a name="EXAMPLE_OPTION_FDIN"></a>
<a name="EXAMPLE_OPTION_FDOUT"></a>
<a name="EXAMPLE_OPTION_CRNL"></a>
<a name="EXAMPLE_OPTION_MSS"></a>

<dt><code>socat EXEC:"mail.sh target@domain.com",fdin=3,fdout=4 \ 
TCP4:mail.relay.org:25,crnl,bind=alias1.server.org,mss=512</code><dd>

mail.sh is a shell script, distributed with socat, that implements a
simple 
SMTP client. It is programmed to "speak" SMTP on its FDs 3 (in) and 4 (out).
The <a href="socat.html#OPTION_FDIN">fdin</a> and <a href="socat.html#OPTION_FDOUT">fdout</a> options tell socat
to use these FDs for communication with 
the program. Because mail.sh inherits stdin and stdout while socat does not
use them, the script can read a
mail body from stdin. Socat makes alias1 your local source address
(<a href="socat.html#OPTION_BIND">bind</a>), cares for correct network line termination
(<a href="socat.html#OPTION_CRNL">crnl</a>) and sends 
at most 512 data bytes per packet (<a href="socat.html#OPTION_MSS">mss</a>). 

<a name="EXAMPLE_ADDRESS_GOPEN"></a>
<a name="EXAMPLE_OPTION_TERMIOS_RAWER"></a>
<a name="EXAMPLE_OPTION_ESCAPE"></a>
<dt><code>socat -,escape=0x0f /dev/ttyS0,rawer,crnl</code><dd>

opens an interactive connection via the serial line, e.g. for talking with a
modem. <a href="socat.html#OPTION_TERMIOS_RAWER">rawer</a> sets the console's and
ttyS0's terminal parameters to practicable values, <a href="socat.html#OPTION_CRNL">crnl</a> 
converts to correct newline characters. <a href="socat.html#OPTION_ESCAPE">escape</a> allows
terminating the socat process with character control-O. 
Consider using <a href="socat.html#ADDRESS_READLINE">READLINE</a> instead of the first address.

<a name="EXAMPLE_ADDRESS_UNIX_LISTEN"></a>
<a name="EXAMPLE_ADDRESS_SOCKS4"></a>
<a name="EXAMPLE_OPTION_SOCKSUSER"></a>
<a name="EXAMPLE_OPTION_SOURCEPORT"></a>

<dt><code>socat UNIX-LISTEN:/tmp/.X11-unix/X1,fork \ 
SOCKS4:host.victim.org:127.0.0.1:6000,socksuser=nobody,sourceport=20</code><dd>

with <a href="socat.html#ADDRESS_UNIX_LISTEN">UNIX-LISTEN</a>, socat opens a listening
UNIX domain socket /tmp/.X11-unix/X1. This path corresponds 
to local XWindow display :1 on your machine, so XWindow client connections to
DISPLAY=:1 are accepted. Socat then speaks with
the <a href="socat.html#ADDRESS_SOCKS4">SOCKS4</a> server host.victim.org that might permit 
<a href="socat.html#OPTION_SOURCEPORT">sourceport</a> 20 based connections due to an FTP related
weakness in its static IP filters. Socat
pretends to be invoked by <a href="socat.html#OPTION_SOCKSUSER">socksuser</a> nobody, and
requests to be connected to 
loopback port 6000 (only weak sockd configurations will allow this). So we get
a connection to the victims XWindow server and, if it does not require MIT
cookies or Kerberos authentication, we can start work. Please note that there
can only be one connection at a time, because TCP can establish only one
session with a given set of addresses and ports.

<a name="EXAMPLE_option_u"></a>
<a name="EXAMPLE_OPTION_IGNOREEOF"></a>
<dt><code>socat -u /tmp/readdata,seek-end=0,ignoreeof -</code><dd>

this is an example for unidirectional data transfer
(<a href="socat.html#option_u">-u</a>). Socat transfers data 
from file /tmp/readdata (implicit address <a href="socat.html#ADDRESS_GOPEN">GOPEN</a>), starting
at its current end (<a href="socat.html#OPTION_SEEK_END">seek-end</a>=0 lets socat start 
reading at current end of file; use <a href="socat.html#OPTION_SEEK">seek</a>=0 or no
seek option to first read the existing data) in a "tail -f" like mode
(<a href="socat.html#OPTION_IGNOREEOF">ignoreeof</a>). The "file" 
might also be a listening UNIX domain socket (do not use a seek option then). 

<a name="EXAMPLE_OPTION_SETSID"></a>
<a name="EXAMPLE_OPTION_CTTY"></a>

<dt><code>(sleep 5; echo PASSWORD; sleep 5; echo ls; sleep 1) | 
socat - EXEC:'ssh -l user server',pty,setsid,ctty</code><dd>

<a href="socat.html#ADDRESS_EXEC">EXEC</a>'utes an ssh session to server. Uses a <a href="socat.html#OPTION_PTY">pty</a> for communication between socat and
ssh, makes it ssh's controlling tty (<a href="socat.html#OPTION_CTTY">ctty</a>), 
and makes this pty the owner of
a new process group (<a href="socat.html#OPTION_SETSID">setsid</a>), so ssh accepts the password from socat.

<a name="EXAMPLE_ADDRESS_OPEN"></a>
<a name="EXAMPLE_OPTION_CREAT"></a>
<a name="EXAMPLE_OPTION_APPEND"></a>

<dt><code>socat -u TCP4-LISTEN:3334,reuseaddr,fork \ 
OPEN:/tmp/in.log,creat,append</code><dd>

implements a simple network based message collector. 
For each client connecting to port 3334, a new child process is generated (option <a href="socat.html#OPTION_FORK">fork</a>).
All data sent by the clients are <a href="socat.html#OPTION_APPEND">append</a>'ed to the file /tmp/in.log.
If the file does not exist, socat <a href="socat.html#OPTION_O_CREAT">creat</a>'s it. 
Option <a href="socat.html#OPTION_REUSEADDR">reuseaddr</a> allows immediate restart of the server
process.

<a name="EXAMPLE_OPTION_NOECHO"></a>
<dt><code>socat READLINE,noecho='[Pp]assword:' EXEC:'ftp ftp.server.com',pty,setsid,ctty</code><dd>

wraps a command line history (<a href="socat.html#ADDRESS_READLINE">READLINE</a>) around the <a href="socat.html#ADDRESS_EXEC">EXEC</a>'uted ftp client utility.
This allows editing and reuse of FTP commands for relatively comfortable
browsing through the ftp directory hierarchy. The password is echoed!
 <a href="socat.html#OPTION_PTY">pty</a> is required to have ftp issue a prompt.
Nevertheless, there may occur some confusion with the password and FTP
prompts.

<a name="EXAMPLE_ADDRESS_PTY"></a>
<a name="EXAMPLE_OPTION_SYMBOLIC_LINK"></a>
<a name="EXAMPLE_OPTION_WAIT_SLAVE"></a>
<a name="EXAMPLE_OPTION_NONBLOCK"></a>

<dt><code>socat PTY,link=$HOME/dev/vmodem0,rawer,wait-slave \ 
EXEC:'"ssh modemserver.us.org socat - /dev/ttyS0,nonblock,rawer"'</code><dd>

generates a pseudo terminal 
device (<a href="socat.html#ADDRESS_PTY">PTY</a>) on the client that can be reached under the
symbolic <a href="socat.html#OPTION_SYMBOLIC_LINK">link</a> $HOME/dev/vmodem0. 
An application that expects a serial line or modem
can be configured to use $HOME/dev/vmodem0; its traffic will be directed
to a modemserver via ssh where another socat instance links it to
/dev/ttyS0.

<dt><code>socat TCP4-LISTEN:2022,reuseaddr,fork \ 
PROXY:proxy:www.domain.org:22,proxyport=3128,proxyauth=user:pass</code><dd>

starts a forwarder that accepts connections on port 2022, and directs them 
through the <a href="socat.html#ADDRESS_PROXY_CONNECT">proxy</a> daemon listening on port 3128
(<a href="socat.html#OPTION_PROXYPORT">proxyport</a>) on host proxy, using the
CONNECT method, where they are authenticated as "user" with "pass" (<a href="socat.html#OPTION_PROXY_AUTHORIZATION">proxyauth</a>). The proxy 
should establish connections to host www.domain.org on port 22 then.

<a name="EXAMPLE_ADDRESS_OPENSSL_CONNECT"></a>
<dt><code>socat - SSL:server:4443,cafile=server.crt,cert=client.pem</code><dd>

is an OpenSSL client that tries to establish a secure connection to an SSL
server. Option <a href="socat.html#OPTION_OPENSSL_CAFILE">cafile</a> specifies a file that
contains trust certificates: we trust the server only when it presents one of
these certificates and proofs that it owns the related private key. 
Otherwise the connection is terminated.
With <a href="socat.html#OPTION_OPENSSL_CERTIFICATE">cert</a> a file containing the client certificate
and the associated private key is specified. This is required in case the
server wishes a client authentication; many Internet servers do not. 
The first address ('-') can be replaced by almost any other socat address.

<a name="EXAMPLE_ADDRESS_OPENSSL_LISTEN"></a>
<dt><code>socat OPENSSL-LISTEN:4443,reuseaddr,pf=ip4,fork,cert=server.pem,cafile=client.crt PIPE</code><dd>

is an OpenSSL server that accepts TCP connections, presents the certificate
from the file server.pem and forces the client to present a certificate that is
verified against cafile.crt. 
The second address ('PIPE') can be replaced by almost any other socat
address. 
For instructions on generating and distributing OpenSSL keys and certificates
see the additional socat docu <code>socat-openssl.txt</code>.

<dt><code>echo |socat -u - file:/tmp/bigfile,create,largefile,seek=100000000000</code><dd>

creates a 100GB sparse file; this requires a file system type that
supports this (ext2, ext3, reiserfs, jfs; not minix, vfat). The operation of
writing 1 byte might take long (reiserfs: some minutes; ext2: "no" time), and
the resulting file can consume some disk space with just its inodes (reiserfs:
2MB; ext2: 16KB). 

<dt><code>socat tcp-l:7777,reuseaddr,fork system:'filan -i 0 -s &gt;&amp;2',nofork</code><dd>

listens for incoming TCP connections on port 7777. For each accepted
connection, invokes a shell. This shell has its stdin and stdout directly
connected to the TCP socket (<a href="socat.html#OPTION_NOFORK">nofork</a>). The shell starts filan and lets it print the socket addresses to
stderr (your terminal window).

<dt><code>echo -e "\0\14\0\0\c" |socat -u - file:/usr/bin/squid.exe,seek=0x00074420</code><dd>

functions as primitive binary editor: it writes the 4 bytes 000 014 000 000 to
the executable /usr/bin/squid at offset 0x00074420 (this is a real world patch
to make the squid executable from Cygwin run under Windows, actual per May 2004).

<dt><code>socat - tcp:www.blackhat.org:31337,readbytes=1000</code><dd>

connects to an unknown service and prevents being flooded.

<a name="EXAMPLE_END_CLOSE"></a>
<dt><code>socat -U TCP:target:9999,end-close TCP-L:8888,reuseaddr,fork</code><dd>

merges data arriving from different TCP streams on port 8888 to just one stream
to target:9999. The <a href="socat.html#OPTION_END_CLOSE">end-close</a> option prevents the child
processes forked off by the second address from terminating the shared
connection to 9999 (close(2) just unlinks the inode which stays active as long
as the parent process lives; shutdown(2) would actively terminate the
connection).

<a name="EXAMPLE_ADDRESS_UDP4_BROADCAST_CLIENT"></a>
<dt><code>socat - UDP4-DATAGRAM:192.168.1.0:123,sp=123,broadcast,range=192.168.1.0/24</code><dd>

sends a broadcast to the network 192.168.1.0/24 and receives the replies of the
timeservers there. Ignores NTP packets from hosts outside this network.

<a name="EXAMPLE_ADDRESS_GENERIC_CLIENT"></a>
<dt><code>socat - SOCKET-DATAGRAM:2:2:17:x007bxc0a80100x0000000000000000,bind=x007bx00000000x0000000000000000,setsockopt-int=1:6:1,range=x0000xc0a80100x0000000000000000:x0000xffffff00x0000000000000000</code><dd>

is semantically equivalent to the <a href="socat.html#EXAMPLE_ADDRESS_UDP4_BROADCAST_CLIENT">previous
example</a>, but all parameters are
specified in generic form. the value 6 of setsockopt-int is the Linux value for
<code>SO_BROADCAST</code>.

<a name="EXAMPLE_ADDRESS_IP4_BROADCAST_CLIENT"></a>
<dt><code>socat - IP4-DATAGRAM:255.255.255.255:44,broadcast,range=10.0.0.0/8</code><dd>

sends a broadcast to the local network(s) using protocol 44. Accepts replies
from the private address range only.

<a name="EXAMPLE_ADDRESS_UDP4_MULTICAST"></a>
<dt><code>socat - UDP4-DATAGRAM:224.255.0.1:6666,bind=:6666,ip-add-membership=224.255.0.1:eth0</code><dd>

transfers data from stdin to the specified multicast address using UDP. Both
local and remote ports are 6666. Tells the interface eth0 to also accept
multicast packets of the given group. Multiple hosts on the local network can
run this command, so all data sent by any of the hosts will be received
by all the other ones. Note that there are many possible reasons for failure,
including IP-filters, routing issues, wrong interface selection by the
operating system, bridges, or a badly configured switch.

<a name="EXAMPLE_ADDRESS_TUN"></a>
<dt><code>socat UDP:host2:4443 TUN:192.168.255.1/24,up</code><dd>

establishes one side of a virtual (but not private!) network with host2 where a
similar process might run, with UDP-L and tun address 192.168.255.2. They can
reach each other using the addresses 192.168.255.1 and 192.168.255.2. Note that
streaming eg.via TCP or SSL does not guarantee to retain packet boundaries and
might thus cause packet loss.

<a name="EXAMPLE_ADDRESS_VSOCK"></a>
<dt><code>socat - VSOCK-CONNECT:2:1234</code><dd>

establishes a VSOCK connection with the host (host is always reachable with
the well-know CID=2) on 1234 port.

<dt><code>socat - VSOCK-LISTEN:1234</code><dd>

listens for a VSOCK connection on 1234 port.

<dt><code>socat - VSOCK-CONNECT:31:4321,bind:5555</code><dd>

establishes a VSOCK connection with the guest that have CID=31 on 1234 port,
binding the local socket to the 5555 port.

<dt><code>socat VSOCK-LISTEN:3333,reuseaddr,fork VSOCK-CONNECT:42,3333</code><dd>

starts a forwarder that accepts VSOCK connections on port 3333, and directs
them to the guest with CID=42 on the same port.

<dt><code>socat VSOCK-LISTEN:22,reuseaddr,fork TCP:localhost:22</code><dd>

forwards VSOCK connections from 22 port to the local SSH server.
Running this in a VM allows you to connect via SSH from the host using VSOCK,
as in the example below.

<dt><code>socat TCP4-LISTEN:22222,reuseaddr,fork VSOCK-CONNECT:33:22</code><dd>

forwards TCP connections from 22222 port to the guest with CID=33 listening on
VSOCK port 22.
Running this in the host, allows you to connect via SSH running
"ssh -p 22222 user@localhost", if the guest runs the example above.

<a name="EXAMPLE_INTERFACE"></a>
<dt><code>socat PTY,link=/var/run/ppp,rawer INTERFACE:hdlc0</code><dd>

circumvents the problem that pppd requires a serial device and thus might not
be able to work on a synchronous line that is represented by a network device.
socat creates a PTY to make pppd happy, binds to the network
<a href="socat.html#ADDRESS_INTERFACE">interface</a> <code>hdlc0</code>, and can transfer data between
both devices. Use pppd on device <code>/var/run/ppp</code> then.

<a name="EXAMPLE_HTTPECHO"></a>
<dt><code>socat -T 1 -d -d TCP-L:10081,reuseaddr,fork,crlf SYSTEM:"echo -e \"\\\"HTTP/1.0 200 OK\\\nDocumentType: text/plain\\\n\\\ndate: \$$date$\\\nserver:\$SOCAT_SOCKADDR:\$SOCAT_SOCKPORT\\\nclient: \$SOCAT_PEERADDR:\$SOCAT_PEERPORT\\\n\\\"\"; cat; echo -e \"\\\"\\\n\\\"\""</code><dd>

creates a simple HTTP echo server: each HTTP client that connects gets a valid
HTTP reply that contains information about the client address and port as it is
seen by the server host, the host address (which might vary on multihomed
servers), and the original client request.

<a name="EXAMPLE_ANCILLARY"></a>
<dt><code>socat -d -d UDP4-RECVFROM:9999,so-broadcast,so-timestamp,ip-pktinfo,ip-recverr,ip-recvopts,ip-recvtos,ip-recvttl!!- SYSTEM:'export; sleep 1' |grep SOCAT</code><dd>

waits for an incoming UDP packet on port 9999 and prints the environment 
variables provided by socat. On BSD based systems you have to replace
<a href="socat.html#OPTION_IP_PKTINFO"><code>ip-pktinfo</code></a> with <a href="socat.html#OPTION_IP_RECVDSTADDR"><code>ip-recvdstaddr</code></a>,<a href="socat.html#OPTION_IP_RECVIF"><code>ip-recvif</code></a>. Especially interesting is
SOCAT_IP_DSTADDR: it contains the target address of the packet which may be a
unicast, multicast, or broadcast address.

<a name="EXAMPLE_SSD"></a>
<dt><code>echo -e "M-SEARCH * HTTP/1.1\nHOST: 239.255.255.250:1900\nMAN: \"ssdp:discover\"\nMX: 4\nST: \"ssdp:all\"\n" |./socat - UDP-DATAGRAM:239.255.255.250:1900,crlf</code><dd>

sends an SSDP (Simple Service Discovery Protocol) query to the local network
and collects and outputs the answers received.

<dt><code></code><dd>

</dl>

<a name="DIAGNOSTICS"></a>
<h2>DIAGNOSTICS</h2>

Socat uses a logging mechanism that allows filtering messages by severity. The
severities provided are more or less compatible to the appropriate syslog
priority. With one or up to four occurrences of the -d command line option, the
lowest priority of messages that are issued can be selected. Each message
contains a single uppercase character specifying the messages severity (one of
F, E, W, N, I, or D)

<dl>
<dt>FATAL:<dd> Conditions that require unconditional and immediate program termination.
<dt>ERROR:<dd> Conditions that prevent proper program processing. Usually the
program is terminated (see <a href="socat.html#option_s">option -s</a>).
<dt>WARNING:<dd> Something did not function correctly or is in a state where
correct further processing cannot be guaranteed, but might be possible.
<dt>NOTICE:<dd> Interesting actions of the program, e.g. for supervising socat in some kind of server mode.
<dt>INFO:<dd> Description of what the program does, and maybe why it
happens. Allows monitoring the lifecycles of file descriptors.
<dt>DEBUG:<dd> Description of how the program works, all system or library calls and their results.
</dl>

Log messages can be written to stderr, to a file, or to syslog.

On exit, socat gives status 0 if it terminated due to EOF or inactivity
timeout, with a positive value on error, and with a negative value on fatal
error. 

<a name="FILES"></a>
<h2>FILES</h2>

/usr/bin/socat 
/usr/bin/filan 
/usr/bin/procan

<a name="ENVIRONMENT_VARIABLES"></a>
<h2>ENVIRONMENT VARIABLES</h2>

Input variables carry information from the environment to socat, output
variables are set by socat for use in executed scripts and programs.

In the output variables beginning with "SOCAT" this prefix is actually replaced
by the upper case name of the executable or the value of option
<a href="socat.html#option_lp">-lp</a>.

<dl>
<a name="ENV_SOCAT_DEFAULT_LISTEN_IP"></a>
<dt>SOCAT_DEFAULT_LISTEN_IP (input)<dd> (Values 4 or 6) Sets the IP version to
be used for listen, recv, and recvfrom addresses if no
<a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a> (protocol-family) option is given. Is
overridden by socat options <a href="socat.html#option_4">-4</a> or <a href="socat.html#option_6">-6</a>.

<dt>SOCAT_PREFERRED_RESOLVE_IP (input)<dd> (Values 0, 4, or 6) Sets the IP
version to 
be used when resolving target host names when version is not specified by
address type, option <a href="socat.html#OPTION_PROTOCOL_FAMILY">pf</a> (protocol-family), or
address format. If name resolution does not return a matching entry, the first
result (with differing IP version) is taken. With value 0, socat always selects
the first record and its IP version. 

<dt>SOCAT_FORK_WAIT (input)<dd> Specifies the time (seconds) to sleep the
parent and child processes after successful fork(). Useful for debugging.

<dt>SOCAT_VERSION (output)<dd> Socat sets this variable to its version string,
e.g. <code>"1.7.0.0"</code> for released versions or e.g. <code>"1.6.0.1+envvar"</code> for
temporary versions; can be used in scripts invoked by socat. 

<dt>SOCAT_PID (output)<dd> Socat sets this variable to its process id. In case
of <a href="socat.html#OPTION_FORK">fork</a> address option, SOCAT_PID gets the child processes
id. Forking for <a href="socat.html#ADDRESS_EXEC">exec</a> and <a href="socat.html#ADDRESS_SYSTEM">system</a> does
not change SOCAT_PID.

<dt>SOCAT_PPID (output)<dd> Socat sets this variable to its process id. In
case of <a href="socat.html#OPTION_FORK">fork</a>, SOCAT_PPID keeps the pid of the master process.

<dt>SOCAT_PEERADDR (output)<dd> With passive socket addresses (all LISTEN and
RECVFROM addresses), this variable is set to a string describing the peers
socket address. Port information is not included.

<dt>SOCAT_PEERPORT (output)<dd> With appropriate passive socket addresses
(TCP, UDP, and SCTP - LISTEN and RECVFROM), this variable is set to a string containing the
number of the peer port.

<dt>SOCAT_SOCKADDR (output)<dd> With all LISTEN addresses, this variable is
set to a string describing the local socket address. Port information is not
included <a href="socat.html#EXAMPLE_HTTPECHO">example</a>

<dt>SOCAT_SOCKPORT (output)<dd> With <a href="socat.html#ADDRESS_TCP_LISTEN">TCP-LISTEN</a>,
<a href="socat.html#ADDRESS_UDP_LISTEN">UDP-LISTEN</a>, and
<a href="socat.html#ADDRESS_SCTP_LISTEN">SCTP-LISTEN</a> addresses, this variable is set to the
local port.

<dt>SOCAT_TIMESTAMP (output)<dd> With all RECVFROM addresses where address
option <a href="socat.html#OPTION_SO_TIMESTAMP">so-timestamp</a> is applied, socat sets this
variable to the resulting timestamp.

<dt>SOCAT_IP_OPTIONS (output)<dd> With all IPv4 based RECVFROM addresses where 
address option <a href="socat.html#OPTION_IP_RECVOPTS">ip-recvopts</a> is applied, socat fills
this variable with the IP options of the received packet.

<dt>SOCAT_IP_DSTADDR (output)<dd> With all IPv4 based RECVFROM addresses where
address option <a href="socat.html#OPTION_IP_RECVDSTADDR">ip-recvdstaddr</a> (BSD) or
<a href="socat.html#OPTION_IP_PKTINFO">ip-pktinfo</a> (other platforms) is applied, socat sets
this variable to the destination address of the received packet. This is
particularly useful to identify broadcast and multicast addressed packets.

<dt>SOCAT_IP_IF (output)<dd> With all IPv4 based RECVFROM addresses where
address option <a href="socat.html#OPTION_IP_RECVIF">ip-recvif</a> (BSD) or
<a href="socat.html#OPTION_IP_PKTINFO">ip-pktinfo</a> (other platforms) is applied, socat sets 
this variable to the name of the interface where the packet was received.

<dt>SOCAT_IP_LOCADDR (output)<dd> With all IPv4 based RECVFROM
addresses where address option <a href="socat.html#OPTION_IP_PKTINFO">ip-pktinfo</a> is applied,
socat sets this variable to the address of the interface where the packet was
received.

<dt>SOCAT_IP_TOS (output)<dd> With all IPv4 based RECVFROM addresses where
address option <a href="socat.html#OPTION_IP_RECVTOS">ip-recvtos</a> is applied, socat sets this
variable to the TOS (type of service) of the received packet.

<dt>SOCAT_IP_TTL (output)<dd> With all IPv4 based RECVFROM addresses where
address option <a href="socat.html#OPTION_IP_RECVTTL">ip-recvttl</a> is applied, socat sets this
variable to the TTL (time to live) of the received packet.

<dt>SOCAT_IPV6_HOPLIMIT (output)<dd> With all IPv6 based RECVFROM addresses
where address option <a href="socat.html#OPTION_IPV6_RECVHOPLIMIT">ipv6-recvhoplimit</a> is
applied, socat sets this variable to the hoplimit value of the received packet.

<dt>SOCAT_IPV6_DSTADDR (output)<dd> With all IPv6 based RECVFROM
addresses where address option <a href="socat.html#OPTION_IPV6_RECVPKTINFO">ipv6-recvpktinfo</a>
is applied, socat sets this variable to the destination address of the received
packet.

<dt>SOCAT_IPV6_TCLASS (output)<dd> With all IPv6 based RECVFROM addresses
where address option <a href="socat.html#OPTION_IPV6_RECVTCLASS">ipv6-recvtclass</a> is applied,
socat sets this variable to the transfer class of the received packet.

<dt>SOCAT_OPENSSL_X509_ISSUER (output)<dd> Issuer field from peer certificate

<dt>SOCAT_OPENSSL_X509_SUBJECT (output)<dd> Subject field from peer certificate

<dt>SOCAT_OPENSSL_X509_COMMONNAME (output)<dd> commonName entries from peer certificates subject. Multiple values are separated by " // ".

<dt>SOCAT_OPENSSL_X509_* (output)<dd> all other entries from peer certificates subject

<dt>SOCAT_OPENSSL_X509V3_DNS (output)<dd> DNS entries from peer certificates extensions - subjectAltName field. Multiple values are separated by " // ".

<dt>HOSTNAME (input)<dd> Is used to determine the hostname for logging (see
<a href="socat.html#option_lh">-lh</a>).

<dt>LOGNAME (input)<dd> Is used as name for the socks client user name if no
<a href="socat.html#OPTION_SOCKSUSER">socksuser</a> is given. 
With options <a href="socat.html#OPTION_SUBSTUSER">su</a> and
<a href="socat.html#OPTION_SUBSTUSER_DELAYED">su-d</a>, LOGNAME is set to the given user name.

<dt>USER (input)<dd> Is used as name for the socks client user name if no
<a href="socat.html#OPTION_SOCKSUSER">socksuser</a> is given and LOGNAME is empty. 
With options <a href="socat.html#OPTION_SUBSTUSER">su</a> and
<a href="socat.html#OPTION_SUBSTUSER_DELAYED">su-d</a>, USER is set to the given user name.

<dt>SHELL (output)<dd>
With options <a href="socat.html#OPTION_SUBSTUSER">su</a> and
<a href="socat.html#OPTION_SUBSTUSER_DELAYED">su-d</a>, SHELL is set to the login shell of the
given user.

<dt>PATH (output)<dd>
Can be set with option <a href="socat.html#OPTION_PATH">path</a> for <a href="socat.html#ADDRESS_EXEC">exec</a> and
<a href="socat.html#ADDRESS_SYSTEM">system</a> addresses.

<dt>HOME (output)<dd>
With options <a href="socat.html#OPTION_SUBSTUSER">su</a> and
<a href="socat.html#OPTION_SUBSTUSER_DELAYED">su-d</a>, HOME is set to the home directory of the
given user.

</dl>

<a name="CREDITS"></a>
<h2>CREDITS</h2>

The work of the following groups and organizations was invaluable for this
project:

The FSF (GNU, <a href="http://www.fsf.org/">http://www.fsf.org/</a> project 
with their free and portable development software and
lots of other useful tools and libraries.

The Linux developers community (<a href="http://www.linux.org/">http://www.linux.org/</a>) for providing a free, open source operating
system.

The Open Group (<a href="http://www.unix-systems.org/">http://www.unix-systems.org/</a>) for making their
standard specifications available on the Internet for free.

<a name="VERSION"></a>
<h2>VERSION</h2>

This man page describes version 1.7.4 of socat.

<a name="BUGS"></a>
<h2>BUGS</h2>

Addresses cannot be nested, so a single socat process cannot, e.g., drive ssl
over socks.

Address option ftruncate without value uses default 1 instead of 0.

Verbose modes (-x and/or -v) display line termination characters inconsistently
when address options cr or crnl are used: They show the data after
conversion in either direction.

The data transfer blocksize setting (-b) is ignored with address readline.

Send bug reports to &lt;socat@dest-unreach.org&gt;

<a name="SEEALSO"></a>
<h2>SEE ALSO</h2>

nc(1), rinetd(8), openssl(1),
stunnel(8), rlwrap(1), setsid(1)

Socat home page <a href="http://www.dest-unreach.org/socat/">http://www.dest-unreach.org/socat/</a>

<a name="AUTHOR"></a>
<h2>AUTHOR</h2>

Gerhard Rieger &lt;rieger@dest-unreach.org&gt; and contributors

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Code Editor : socat.html