/doc/socat.1

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.TH "socat" "1" "Mar 2014" "" ""

.PP 
.SH "NAME"
socat \- Multipurpose relay (SOcket CAT)
.PP 
.SH "SYNOPSIS"
\f(CWsocat [options] <address> <address>\fP
.br 
\f(CWsocat \-V\fP
.br 
\f(CWsocat \-h[h[h]] | \-?[?[?]]\fP
.br 
\f(CWfilan\fP
.br 
\f(CWprocan\fP
.PP 
.SH "DESCRIPTION"

.PP 
\fBSocat\fP 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 address types), and because lots of
address options may be applied to the streams, socat can
be used for many different purposes\&. 
.PP 
\fBFilan\fP is a utility that prints information about its active file
descriptors to stdout\&. It has been written for debugging \fBsocat\fP, but might be
useful for other purposes too\&. Use the \-h option to find more infos\&.
.PP 
\fBProcan\fP 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 \fBsocat\fP, but might be 
useful for other purposes too\&.
.PP 
The life cycle of a \fBsocat\fP instance typically consists of four phases\&.
.PP 
In the \fIinit\fP phase, the command line options are parsed and logging is
initialized\&. 
.PP 
During the \fIopen\fP phase, \fBsocat\fP 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\&.
.PP 
In the \fItransfer\fP phase, \fBsocat\fP watches both streams\(cq\& read and write file
descriptors via 
\f(CWselect()\fP
, and, when data is available on one side \fIand\fP
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\&.
.PP 
When one of the streams effectively reaches EOF, the \fIclosing\fP phase
begins\&. \fBSocat\fP 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 \fBsocat\fP continues to transfer data in
the other direction, but then closes all remaining channels and terminates\&.
.PP 
.SH "OPTIONS"

.PP 
\fBSocat\fP provides some command line options that modify the behaviour of the
program\&. They have nothing to do with so called
address options that are used as parts of address specifications\&.
.PP 
.IP "\fB\f(CW\-V\fP\fP"
Print version and available feature information to stdout, and exit\&.
.IP "\fB\f(CW\-h | \-?\fP\fP"
Print a help text to stdout describing command line options and available address
types, and exit\&.
.IP "\fB\f(CW\-hh | \-??\fP\fP"
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\&. 
.IP "\fB\f(CW\-hhh | \-???\fP\fP"
Like \-hh, plus a list of all available address option names\&.
.IP "\fB\f(CW\-d\fP\fP"
Without this option, only fatal and error messages are generated; applying
this option also prints warning messages\&. See DIAGNOSTICS
for more information\&. 
.IP "\fB\f(CW\-d \-d\fP\fP"
Prints fatal, error, warning, and notice messages\&.
.IP "\fB\f(CW\-d \-d \-d\fP\fP"
Prints fatal, error, warning, notice, and info messages\&.
.IP "\fB\f(CW\-d \-d \-d \-d\fP\fP"
Prints fatal, error, warning, notice, info, and debug
messages\&. 
.IP "\fB\f(CW\-D\fP\fP"
Logs information about file descriptors before starting the transfer phase\&.
.IP "\fB\f(CW\-ly[<facility>]\fP\fP"
Writes messages to syslog instead of stderr; severity as defined with \-d
option\&. With optional <facility>, the syslog type can
be selected, default is \(dq\&daemon\(dq\&\&. Third party libraries might not obey this
option\&.
.IP "\fB\f(CW\-lf\fP\fP\f(CW <logfile>\fP"
Writes messages to <logfile> [filename] instead of
stderr\&. Some third party libraries, in particular libwrap, might not obey
this option\&.
.IP "\fB\f(CW\-ls\fP\fP"
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\&. 
.IP "\fB\f(CW\-lp\fP\fP\f(CW<progname>\fP"
Overrides the program name printed in error messages and used for
constructing environment variable names\&.
.IP "\fB\f(CW\-lu\fP\fP"
Extends the timestamp of error messages to microsecond resolution\&. Does not
work when logging to syslog\&.
.IP "\fB\f(CW\-lm[<facility>]\fP\fP"
Mixed log mode\&. During startup messages are printed to stderr; when \fBsocat\fP 
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 <facility>, the syslog type can be
selected, default is \(dq\&daemon\(dq\&\&. 
.IP "\fB\f(CW\-lh\fP\fP"
Adds hostname to log messages\&. Uses the value from environment variable
HOSTNAME or the value retrieved with \f(CWuname()\fP if HOSTNAME is not set\&.
.IP "\fB\f(CW\-v\fP\fP"
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 \(dq\&> \(dq\& or \(dq\&< \(dq\& indicating flow directions\&.
.IP "\fB\f(CW\-x\fP\fP"
Writes the transferred data not only to their target streams, but also to
stderr\&. The output format is hexadecimal, prefixed with \(dq\&> \(dq\& or \(dq\&< \(dq\&
indicating flow directions\&. Can be combined with 
\f(CW\-v\fP
\&.
.IP "\fB\f(CW\-b\fP\fP\f(CW<size>\fP"
Sets the data transfer block <size> [size_t]\&.
At most <size> bytes are transferred per step\&. Default is 8192 bytes\&. 
.IP "\fB\f(CW\-s\fP\fP"
By default, \fBsocat\fP terminates when an error occurred to prevent the process
from running when some option could not be applied\&. With this
option, \fBsocat\fP 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\&.
.IP "\fB\f(CW\-t\fP\fP\f(CW<timeout>\fP"
When one channel has reached EOF, the write part of the other channel is shut
down\&. Then, \fBsocat\fP waits <timeout> [timeval] 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\&.
.IP "\fB\f(CW\-T\fP\fP\f(CW<timeout>\fP"
Total inactivity timeout: when socat is already in the transfer loop and
nothing has happened for <timeout> [timeval] seconds
(no data arrived, no interrupt occurred\&.\&.\&.) then it terminates\&.
Useful with protocols like UDP that cannot transfer EOF\&.
.IP "\fB\f(CW\-u\fP\fP"
Uses unidirectional mode\&. The first address is only used for reading, and the
second address is only used for writing (example)\&. 
.IP "\fB\f(CW\-U\fP\fP"
Uses unidirectional mode in reverse direction\&. The first address is only
used for writing, and the second address is only used for reading\&. 
.IP "\fB\f(CW\-g\fP\fP"
During address option parsing, don\(cq\&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\&.
.IP "\fB\f(CW\-L\fP\fP\f(CW<lockfile>\fP"
If lockfile exists, exits with error\&. If lockfile does not exist, creates it
and continues, unlinks lockfile on exit\&.
.IP "\fB\f(CW\-W\fP\fP\f(CW<lockfile>\fP"
If lockfile exists, waits until it disappears\&. When lockfile does not exist,
creates it and continues, unlinks lockfile on exit\&.
.IP "\fB\f(CW\-4\fP\fP"
Use IP version 4 in case that the addresses do not implicitly or explicitly
specify a version; this is the default\&.
.IP "\fB\f(CW\-6\fP\fP"
Use IP version 6 in case that the addresses do not implicitly or explicitly
specify a version\&.

.PP 
.SH "ADDRESS SPECIFICATIONS"

.PP 
With the address command line arguments, the user gives \fBsocat\fP instructions and
the necessary information for establishing the byte streams\&. 
.PP 
An address specification usually consists of an address type
keyword, zero or more required address parameters separated by \(cq\&:\(cq\& from the keyword and
from each 
other, and zero or more address options separated by \(cq\&,\(cq\&\&. 
.PP 
The keyword specifies the address type (e\&.g\&., TCP4, OPEN, EXEC)\&. For some
keywords there exist synonyms (\(cq\&\-\(cq\& 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 \(cq\&/\(cq\& is found before the first \(cq\&:\(cq\& or \(cq\&,\(cq\&, GOPEN (generic file open) is
assumed\&. 
.PP 
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)\&. 
.PP 
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 \(cq\&=\(cq\&\&. 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 option \-g)\&. 
.PP 
Address specifications following the above schema are also called \fIsingle\fP
address specifications\&.
Two single addresses can be combined with \(dq\&!!\(dq\& to form a \fIdual\fP type
address for one channel\&. Here, the first address is used by \fBsocat\fP 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\&.
.PP 
Usually, addresses are opened in read/write
mode\&. When an address is part of a dual address specification, or when
option \-u or \-U is used, an address might be
used only for reading or for writing\&. Considering this is important with some
address types\&.
.PP 
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 ( { [ \(cq\& is found, the corresponding closing 
character \- ) } ] \(cq\& \- 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 \e or within \(dq\&\(dq\&
.PP 
.SH "ADDRESS TYPES"

.PP 
This section describes the available address types with their keywords,
parameters, and semantics\&.
.PP 
.IP "\fB\f(CWCREATE:<filename>\fP\fP"
Opens <filename> with 
\f(CWcreat()\fP
and uses the file
descriptor for writing\&. 
This address type requires write\-only context, because a file opened with
\f(CWcreat\fP
cannot be read from\&. 
.br 
Flags like O_LARGEFILE cannot be applied\&. If you need them use
OPEN with options
create,create\&. 
.br 
<filename> must be a valid existing or not existing path\&.
If <filename> is a named pipe, 
\f(CWcreat()\fP
might block;
if <filename> refers to a socket, this is an error\&.
.br 
Option groups: FD,REG,NAMED 
.br 
Useful options:
mode,
user,
group,
unlink\-early,
unlink\-late,
append
.br 
See also: OPEN, GOPEN
.IP "\fB\f(CWEXEC:<command\-line>\fP\fP"
Forks a sub process that establishes communication with its parent process
and invokes the specified program with 
\f(CWexecvp()\fP
\&.
<command\-line> is a simple command
with arguments separated by single spaces\&. If the program name
contains a \(cq\&/\(cq\&, the part after the last \(cq\&/\(cq\& is taken as ARGV[0]\&. If the
program name is a relative 
path, the 
\f(CWexecvp()\fP
semantics for finding the program via
\f(CW$PATH\fP
apply\&. After successful program start, \fBsocat\fP writes data to stdin of the
process and reads from its stdout using a UNIX domain socket generated by
\f(CWsocketpair()\fP
per default\&. (example) 
.br 
Option groups: FD,SOCKET,EXEC,FORK,TERMIOS 
.br 
Useful options:
path,
fdin,
fdout,
chroot,
su,
su\-d,
nofork,
pty,
stderr,
ctty,
setsid,
pipes,
login,
sigint,
sigquit
.br 
See also: SYSTEM
.IP "\fB\f(CWFD:<fdnum>\fP\fP"
Uses the file descriptor <fdnum>\&. It must already exist as
valid UN*X file descriptor\&.
.br 
Option groups: FD (TERMIOS,REG,SOCKET) 
.br 
See also:
STDIO,
STDIN,
STDOUT,
STDERR 
.IP "\fB\f(CWGOPEN:<filename>\fP\fP"
(Generic open) This address type tries to handle any file system entry
except directories usefully\&. <filename> may be a
relative or absolute path\&. If it already exists, its type is checked\&. 
In case of a UNIX domain socket, \fBsocat\fP connects; if connecting fails,
\fBsocat\fP assumes a datagram socket and uses 
\f(CWsendto()\fP
calls\&.
If the entry is not a socket, \fBsocat\fP opens it applying the 
\f(CWO_APPEND\fP
flag\&. 
If it does not exist, it is opened with flag
\f(CWO_CREAT\fP
as a regular file (example)\&.
.br 
Option groups: FD,REG,SOCKET,NAMED,OPEN 
.br 
See also:
OPEN,
CREATE,
UNIX\-CONNECT
.IP 
.IP "\fB\f(CWIP\-SENDTO:<host>:<protocol>\fP\fP"
Opens a raw IP socket\&. Depending on host specification or option pf, IP protocol version
4 or 6 is used\&. It uses <protocol> to send packets
to <host> [IP address] 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\&.
.br 
Option groups: FD,SOCKET,IP4,IP6 
.br 
Useful options:
pf,
ttl 
.br 
See also:
IP4\-SENDTO,
IP6\-SENDTO,
IP\-RECVFROM,
IP\-RECV,
UDP\-SENDTO,
UNIX\-SENDTO
.IP "\fB\f(CWINTERFACE:<interface>\fP\fP"
Communicates with a network connected on an interface using raw packets
including link level data\&. <interface> is the name of
the network interface\&. Currently only available on Linux\&.
Option groups: FD,SOCKET 
.br 
Useful options:
pf,
type
.br 
See also: ip\-recv
.IP "\fB\f(CWIP4\-SENDTO:<host>:<protocol>\fP\fP"
Like IP\-SENDTO, but always uses IPv4\&.
.br 
Option groups: FD,SOCKET,IP4 
.br 
.IP "\fB\f(CWIP6\-SENDTO:<host>:<protocol>\fP\fP"
Like IP\-SENDTO, but always uses IPv6\&.
.br 
Option groups: FD,SOCKET,IP6 
.br 

.IP 
.IP "\fB\f(CWIP\-DATAGRAM:<address>:<protocol>\fP\fP"
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
RANGE or TCPWRAP
options\&. This address type can for example be used for implementing
symmetric or asymmetric broadcast or multicast communications\&.
.br 
Option groups: FD, SOCKET,
IP4, IP6, RANGE 
.br 
Useful options:
bind,
range,
tcpwrap,
broadcast,
ip\-multicast\-loop,
ip\-multicast\-ttl,
ip\-multicast\-if,
ip\-add\-membership,
ttl,
tos,
pf
.br 
See also:
IP4\-DATAGRAM,
IP6\-DATAGRAM,
IP\-SENDTO,
IP\-RECVFROM,
IP\-RECV,
UDP\-DATAGRAM
.IP "\fB\f(CWIP4\-DATAGRAM:<host>:<protocol>\fP\fP"
Like IP\-DATAGRAM, but always uses IPv4\&.
(example)
.br 
Option groups: FD,SOCKET,IP4,RANGE 
.br 
.IP "\fB\f(CWIP6\-DATAGRAM:<host>:<protocol>\fP\fP"
Like IP\-DATAGRAM, but always uses IPv6\&. Please
note that IPv6 does not know broadcasts\&.
.br 
Option groups: FD,SOCKET,IP6,RANGE 
.br 

.IP 
.IP "\fB\f(CWIP\-RECVFROM:<protocol>\fP\fP"
Opens a raw IP socket of <protocol>\&. Depending on option pf, 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\&.
.br 
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\&.
.br 
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\&.
.br 
Option groups: FD,SOCKET,IP4,IP6,CHILD,RANGE 
.br 
Useful options:
pf,
fork,
range,
ttl,
broadcast
.br 
See also:
IP4\-RECVFROM,
IP6\-RECVFROM,
IP\-SENDTO,
IP\-RECV,
UDP\-RECVFROM,
UNIX\-RECVFROM 
.IP "\fB\f(CWIP4\-RECVFROM:<protocol>\fP\fP"
Like IP\-RECVFROM, but always uses IPv4\&.
.br 
Option groups: FD,SOCKET,IP4,CHILD,RANGE 
.br 
.IP "\fB\f(CWIP6\-RECVFROM:<protocol>\fP\fP"
Like IP\-RECVFROM, but always uses IPv6\&.
.br 
Option groups: FD,SOCKET,IP6,CHILD,RANGE 
.br 

.IP 
.IP "\fB\f(CWIP\-RECV:<protocol>\fP\fP"
Opens a raw IP socket of <protocol>\&. Depending on option pf, 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\&.
.br 
Option groups: FD,SOCKET,IP4,IP6,RANGE 
.br 
Useful options:
pf,
range
.br 
See also:
IP4\-RECV,
IP6\-RECV,
IP\-SENDTO,
IP\-RECVFROM,
UDP\-RECV,
UNIX\-RECV 
.IP "\fB\f(CWIP4\-RECV:<protocol>\fP\fP"
Like IP\-RECV, but always uses IPv4\&.
.br 
Option groups: FD,SOCKET,IP4,RANGE 
.br 
.IP "\fB\f(CWIP6\-RECV:<protocol>\fP\fP"
Like IP\-RECV, but always uses IPv6\&.
.br 
Option groups: FD,SOCKET,IP6,RANGE 
.br 

.IP 
.IP "\fB\f(CWOPEN:<filename>\fP\fP"
Opens <filename> using the 
\f(CWopen()\fP
system call
(example)\&.
This operation fails on UNIX domain sockets\&. 
.br 
Note: This address type is rarly useful in bidirectional mode\&.
.br 
Option groups: FD,REG,NAMED,OPEN 
.br 
Useful options:
creat,
excl,
noatime,
nofollow,
append,
rdonly,
wronly,
lock,
readbytes,
ignoreeof
.br 
See also:
CREATE,
GOPEN,
UNIX\-CONNECT
.IP "\fB\f(CWOPENSSL:<host>:<port>\fP\fP"
Tries to establish a SSL connection to <port> [TCP
service] on  
<host> [IP address] using TCP/IP version 4 or 6
depending on address specification, name resolution, or option
pf\&.
.br 
NOTE: The server certificate is only checked for validity against
cafile or capath,
but not for match with the server\(cq\&s name or its IP address!
.br 
Option groups: FD,SOCKET,IP4,IP6,TCP,OPENSSL,RETRY 
.br 
Useful options:
cipher,
method,
verify,
cafile,
capath,
certificate,
key,
compress,
bind,
pf,
connect\-timeout,
sourceport,
retry
.br 
See also:
OPENSSL\-LISTEN,
TCP
.IP "\fB\f(CWOPENSSL\-LISTEN:<port>\fP\fP"
Listens on tcp <port> [TCP service]\&.
The IP version is 4 or the one specified with
pf\&. When a
connection is accepted, this address behaves as SSL server\&.
.br 
Note: You probably want to use the certificate option with this address\&.
.br 
NOTE: The client certificate is only checked for validity against
cafile or capath,
but not for match with the client\(cq\&s name or its IP address!
.br 
Option groups: FD,SOCKET,IP4,IP6,TCP,LISTEN,OPENSSL,CHILD,RANGE,RETRY 
.br 
Useful options:
pf,
cipher,
method,
verify,
cafile,
capath,
certificate,
key,
compress,
fork,
bind,
range,
tcpwrap,
su,
reuseaddr,
retry
.br 
See also:
OPENSSL,
TCP\-LISTEN
.IP "\fB\f(CWPIPE:<filename>\fP\fP"
If <filename> 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 unlink\-close
.br 
Note: When a pipe is used for both reading and writing, it works
as echo service\&.
.br 
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\&., 
\f(CW\-b 2048\fP
.br 
Option groups: FD,NAMED,OPEN 
.br 
Useful options:
rdonly,
nonblock,
group,
user,
mode,
unlink\-early
.br 
See also: unnamed pipe
.IP "\fB\f(CWPIPE\fP\fP"
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\&.
.br 
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 
\f(CW\-b 2048\fP
.br 
Option groups: FD 
.br 
See also: named pipe
.IP "\fB\f(CWPROXY:<proxy>:<hostname>:<port>\fP\fP"
Connects to an HTTP proxy server on port 8080 using TCP/IP  version 4 or 6
depending on address specification, name resolution, or option
pf, 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\&. 
.br 
Option groups: FD,SOCKET,IP4,IP6,TCP,HTTP,RETRY 
.br 
Useful options:
proxyport,
ignorecr,
proxyauth,
resolve,
crnl,
bind,
connect\-timeout,
mss,
sourceport,
retry 
.br 
See also: SOCKS, TCP
.IP "\fB\f(CWPTY\fP\fP"
Generates a pseudo terminal (pty) and uses its master side\&. Another process
may open the pty\(cq\&s slave side using it like a serial line or terminal\&.
(example)\&. If
both the ptmx and the openpty mechanisms are available, ptmx is used
(POSIX)\&.
.br 
Option groups: FD,NAMED,PTY,TERMIOS 
.br 
Useful options:
link,
openpty,
wait\-slave,
mode,
user,
group
.br 
See also:
UNIX\-LISTEN,
PIPE,
EXEC, SYSTEM
.IP "\fB\f(CWREADLINE\fP\fP"
Uses GNU readline and history on stdio to allow editing and reusing input
lines (example)\&. This requires the GNU readline and 
history libraries\&. Note that stdio should be a (pseudo) terminal device,
otherwise readline does not seem to work\&.
.br 
Option groups: FD,READLINE,TERMIOS 
.br 
Useful options:
history,
noecho
.br 
See also:
STDIO
.IP "\fB\f(CWSCTP\-CONNECT:<host>:<port>\fP\fP"
Establishes an SCTP stream connection to the specified <host> [IP
address] and <port> [TCP service]
using TCP/IP version 4 or 6 depending on address specification, name
resolution, or option pf\&.
.br 
Option groups: FD,SOCKET,IP4,IP6,SCTP,CHILD,RETRY 
.br 
Useful options:
bind,
pf,
connect\-timeout,
tos,
mtudiscover,
sctp\-maxseg,
sctp\-nodelay,
nonblock,
sourceport,
retry,
readbytes
.br 
See also:
SCTP4\-CONNECT,
SCTP6\-CONNECT,
SCTP\-LISTEN,
TCP\-CONNECT
.IP "\fB\f(CWSCTP4\-CONNECT:<host>:<port>\fP\fP"
Like SCTP\-CONNECT, but only supports IPv4 protocol\&.
.br 
Option groups: FD,SOCKET,IP4,SCTP,CHILD,RETRY 
.br 
.IP "\fB\f(CWSCTP6\-CONNECT:<host>:<port>\fP\fP"
Like SCTP\-CONNECT, but only supports IPv6 protocol\&.
.br 
Option groups: FD,SOCKET,IP6,SCTP,CHILD,RETRY 
.br 
.IP "\fB\f(CWSCTP\-LISTEN:<port>\fP\fP"
Listens on <port> [TCP service] and accepts a
TCP/IP connection\&. The IP version is 4 or the one specified with
address option pf, socat option
(\-4, \-6), or environment variable SOCAT_DEFAULT_LISTEN_IP\&.
Note that opening
this address usually blocks until a client connects\&.
.br 
Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,IP6,SCTP,RETRY 
.br 
Useful options:
crnl,
fork,
bind,
range,
tcpwrap,
pf,
max\-children,
backlog,
sctp\-maxseg,
sctp\-nodelay,
su,
reuseaddr,
retry,
cool\-write
.br 
See also:
SCTP4\-LISTEN,
SCTP6\-LISTEN,
TCP\-LISTEN,
SCTP\-CONNECT
.IP "\fB\f(CWSCTP4\-LISTEN:<port>\fP\fP"
Like SCTP\-LISTEN, but only supports IPv4
protocol\&.
.br 
Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,SCTP,RETRY 
.br 
.IP "\fB\f(CWSCTP6\-LISTEN:<port>\fP\fP"
Like SCTP\-LISTEN, but only supports IPv6
protocol\&.
.br 
Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP6,SCTP,RETRY 
.br 
.IP "\fB\f(CWSOCKET\-CONNECT:<domain>:<protocol>:<remote\-address>\fP\fP"
Creates a stream socket using the first and second given socket parameters
and \f(CWSOCK_STREAM\fP (see man socket\e(2)) and connects to the remote\-address\&.
The two socket parameters have to be specified by int
numbers\&. Consult your OS documentation and include files to find the
appropriate values\&. The remote\-address must be the data
representation of a sockaddr structure without sa_family and (BSD) sa_len
components\&.
.br 
Please note that you can \- beyond the options of the specified groups \- also
use options of higher level protocols when you apply socat option
\-g\&.
.br 
Option groups: FD,SOCKET,CHILD,RETRY
.br 
Useful options:
bind,
setsockopt\-int,
setsockopt\-bin,
setsockopt\-string
.br 
See also:
TCP,
UDP\-CONNECT,
UNIX\-CONNECT,
SOCKET\-LISTEN,
SOCKET\-SENDTO
.IP "\fB\f(CWSOCKET\-DATAGRAM:<domain>:<type>:<protocol>:<remote\-address>\fP\fP"
Creates a datagram socket using the first three given socket parameters (see
man socket\e(2)) and sends outgoing data to the remote\-address\&. The three
socket parameters have to be specified by int
numbers\&. Consult your OS documentation and include files to find the
appropriate values\&. The remote\-address must be the data
representation of a sockaddr structure without sa_family and (BSD) sa_len
components\&.
.br 
Please note that you can \- beyond the options of the specified groups \- also
use options of higher level protocols when you apply socat option
\-g\&.
.br 
Option groups: FD,SOCKET,RANGE
.br 
Useful options:
bind,
range,
setsockopt\-int,
setsockopt\-bin,
setsockopt\-string
.br 
See also:
UDP\-DATAGRAM,
IP\-DATAGRAM,
SOCKET\-SENDTO,
SOCKET\-RECV,
SOCKET\-RECVFROM
.IP "\fB\f(CWSOCKET\-LISTEN:<domain>:<protocol>:<local\-address>\fP\fP"
Creates a stream socket using the first and second given socket parameters
and \f(CWSOCK_STREAM\fP (see man socket\e(2)) and waits for incoming connections
on local\-address\&. The two socket parameters have to be specified by
int numbers\&. Consult your OS documentation and include files
to find the appropriate values\&. The local\-address must be the
data representation of a sockaddr structure without
sa_family and (BSD) sa_len components\&.
.br 
Please note that you can \- beyond the options of the specified groups \- also
use options of higher level protocols when you apply socat option
\-g\&.
.br 
Option groups: FD,SOCKET,LISTEN,RANGE,CHILD,RETRY
.br 
Useful options:
setsockopt\-int,
setsockopt\-bin,
setsockopt\-string
.br 
See also:
TCP,
UDP\-CONNECT,
UNIX\-CONNECT,
SOCKET\-LISTEN,
SOCKET\-SENDTO,
SOCKET\-SENDTO
.IP "\fB\f(CWSOCKET\-RECV:<domain>:<type>:<protocol>:<local\-address>\fP\fP"
Creates a socket using the three given socket parameters (see man socket\e(2))
and binds it to <local\-address>\&. Receives arriving data\&. The three
parameters have to be specified by int numbers\&. Consult your
OS documentation and include files to find the appropriate values\&. The
local\-address must be the data representation of a sockaddr
structure without sa_family and (BSD) sa_len components\&.
.br 
Option groups: FD,SOCKET,RANGE
.br 
Useful options:
range,
setsockopt\-int,
setsockopt\-bin,
setsockopt\-string
.br 
See also:
UDP\-RECV,
IP\-RECV,
UNIX\-RECV,
SOCKET\-DATAGRAM,
SOCKET\-SENDTO,
SOCKET\-RECVFROM
.IP "\fB\f(CWSOCKET\-RECVFROM:<domain>:<type>:<protocol>:<local\-address>\fP\fP"
Creates a socket using the three given socket parameters (see man socket\e(2))
and binds it to <local\-address>\&. Receives arriving data and sends replies
back to the sender\&. The first three parameters have to be specified as
int numbers\&. Consult your OS documentation and include files
to find the appropriate values\&. The local\-address must be the
data representation of a sockaddr structure without
sa_family and (BSD) sa_len components\&.
.br 
Option groups: FD,SOCKET,CHILD,RANGE
.br 
Useful options:
fork,
range,
setsockopt\-int,
setsockopt\-bin,
setsockopt\-string
.br 
See also:
UDP\-RECVFROM,
IP\-RECVFROM,
UNIX\-RECVFROM,
SOCKET\-DATAGRAM,
SOCKET\-SENDTO,
SOCKET\-RECV
.IP "\fB\f(CWSOCKET\-SENDTO:<domain>:<type>:<protocol>:<remote\-address>\fP\fP"
Creates a socket using the three given socket parameters (see man
socket\e(2))\&. Sends outgoing data to the given address and receives replies\&.
The three parameters have to be specified as int
numbers\&. Consult your OS documentation and include files to find the
appropriate values\&. The remote\-address must be the data
representation of a sockaddr structure without sa_family and (BSD) sa_len
components\&.
.br 
Option groups: FD,SOCKET
.br 
Useful options:
bind,
setsockopt\-int,
setsockopt\-bin,
setsockopt\-string
.br 
See also:
UDP\-SENDTO,
IP\-SENDTO,
UNIX\-SENDTO,
SOCKET\-DATAGRAM,
SOCKET\-RECV
SOCKET\-RECVFROM
.IP "\fB\f(CWSOCKS4:<socks\-server>:<host>:<port>\fP\fP"
Connects via <socks\-server> [IP address]
to <host> [IPv4 address]
on <port> [TCP service],
using socks version 4 protocol over IP version 4 or 6 depending on address specification, name resolution, or option
pf (example)\&.
.br 
Option groups: FD,SOCKET,IP4,IP6,TCP,SOCKS4,RETRY 
.br 
Useful options:
socksuser,
socksport,
sourceport,
pf,
retry
.br 
See also:
SOCKS4A,
PROXY,
TCP
.IP "\fB\f(CWSOCKS4A:<socks\-server>:<host>:<port>\fP\fP"
like SOCKS4, but uses socks protocol version 4a, thus
leaving host name resolution to the socks server\&.
.br 
Option groups: FD,SOCKET,IP4,IP6,TCP,SOCKS4,RETRY 
.br 
.IP "\fB\f(CWSTDERR\fP\fP"
Uses file descriptor 2\&.
.br 
Option groups: FD (TERMIOS,REG,SOCKET) 
.br 
See also: FD
.IP "\fB\f(CWSTDIN\fP\fP"
Uses file descriptor 0\&.
.br 
Option groups: FD (TERMIOS,REG,SOCKET) 
.br 
Useful options:
readbytes
.br 
See also: FD
.IP "\fB\f(CWSTDIO\fP\fP"
Uses file descriptor 0 for reading, and 1 for writing\&.
.br 
Option groups: FD (TERMIOS,REG,SOCKET) 
.br 
Useful options:
readbytes
.br 
See also: FD
.IP "\fB\f(CWSTDOUT\fP\fP"
Uses file descriptor 1\&.
.br 
Option groups: FD (TERMIOS,REG,SOCKET) 
.br 
See also: FD
.IP "\fB\f(CWSYSTEM:<shell\-command>\fP\fP"
Forks a sub process that establishes communication with its parent process
and invokes the specified program with 
\f(CWsystem()\fP
\&. Please note that
<shell\-command> [string] must 
not contain \(cq\&,\(cq\& or \(dq\&!!\(dq\&, and that shell meta characters may have to be
protected\&.
After successful program start, \fBsocat\fP writes data to stdin of the 
process and reads from its stdout\&.
.br 
Option groups: FD,SOCKET,EXEC,FORK,TERMIOS 
.br 
Useful options:
path,
fdin,
fdout,
chroot,
su,
su\-d,
nofork,
pty,
stderr,
ctty,
setsid,
pipes,
sigint,
sigquit
.br 
See also: EXEC
.IP "\fB\f(CWTCP:<host>:<port>\fP\fP"
Connects to <port> [TCP service] on
<host> [IP address] using TCP/IP version 4 or 6
depending on address specification, name resolution, or option
pf\&.
.br 
Option groups: FD,SOCKET,IP4,IP6,TCP,RETRY 
.br 
Useful options:
crnl,
bind,
pf,
connect\-timeout,
tos,
mtudiscover,
mss,
nodelay,
nonblock,
sourceport,
retry,
readbytes
.br 
See also:
TCP4,
TCP6,
TCP\-LISTEN,
UDP,
SCTP\-CONNECT,
UNIX\-CONNECT
.IP "\fB\f(CWTCP4:<host>:<port>\fP\fP"
Like TCP, but only supports IPv4 protocol (example)\&.
.br 
Option groups: FD,SOCKET,IP4,TCP,RETRY 
.br 
.IP "\fB\f(CWTCP6:<host>:<port>\fP\fP"
Like TCP, but only supports IPv6 protocol\&.
.br 
Option groups: FD,SOCKET,IP6,TCP,RETRY 
.br 
.IP "\fB\f(CWTCP\-LISTEN:<port>\fP\fP"
Listens on <port> [TCP service] and accepts a
TCP/IP connection\&. The IP version is 4 or the one specified with
address option pf, socat option
(\-4, \-6), or environment variable SOCAT_DEFAULT_LISTEN_IP\&.
Note that opening
this address usually blocks until a client connects\&.
.br 
Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,IP6,TCP,RETRY 
.br 
Useful options:
crnl,
fork,
bind,
range,
tcpwrap,
pf,
max\-children,
backlog,
mss,
su,
reuseaddr,
retry,
cool\-write
.br 
See also:
TCP4\-LISTEN,
TCP6\-LISTEN,
UDP\-LISTEN,
SCTP\-LISTEN,
UNIX\-LISTEN,
OPENSSL\-LISTEN,
TCP\-CONNECT
.IP "\fB\f(CWTCP4\-LISTEN:<port>\fP\fP"
Like TCP\-LISTEN, but only supports IPv4
protocol (example)\&.
.br 
Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,TCP,RETRY 
.br 
.IP "\fB\f(CWTCP6\-LISTEN:<port>\fP\fP"
Like TCP\-LISTEN, but only supports IPv6
protocol\&.
.br 
Additional useful option:
ipv6only
.br 
Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP6,TCP,RETRY 
.br 
.IP "\fB\f(CWTUN[:<if\-addr>/<bits>]\fP\fP"
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 \(dq\&wire side\(dq\&\&. This address
requires read and write access to the tunnel cloning device, usually
\f(CW/dev/net/tun\fP
, as well as permission to set some \f(CWioctl()s\fP\&.
\fBOption iff\-up is required to immediately activate the interface!\fP
.br 
Option groups: FD,NAMED,OPEN,TUN 
.br 
Useful options:
iff\-up,
tun\-device,
tun\-name,
tun\-type,
iff\-no\-pi 
.br 
See also:
ip\-recv
.IP "\fB\f(CWUDP:<host>:<port>\fP\fP"
Connects to <port> [UDP service] on
<host> [IP address] using UDP/IP version 4 or 6
depending on address specification, name resolution, or option
pf\&.
.br 
Please note that,
due to UDP protocol properties, no real connection is established; data has
to be sent for `connecting\(cq\& to the server, and no end\-of\-file condition can
be transported\&.
.br 
Option groups: FD,SOCKET,IP4,IP6 
.br 
Useful options:
ttl,
tos,
bind,
sourceport,
pf
.br 
See also:
UDP4,
UDP6,
UDP\-LISTEN,
TCP,
IP
.IP "\fB\f(CWUDP4:<host>:<port>\fP\fP"
Like UDP, but only supports IPv4 protocol\&.
.br 
Option groups: FD,SOCKET,IP4 
.br 
.IP "\fB\f(CWUDP6:<host>:<port>\fP\fP"
Like UDP, but only supports IPv6 protocol\&.
.br 
Option groups: FD,SOCKET,IP6 
.br 
.IP "\fB\f(CWUDP\-DATAGRAM:<address>:<port>\fP\fP"
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 and if their source addresses match
RANGE or TCPWRAP
options\&. This address type can for example be used for implementing
symmetric or asymmetric broadcast or multicast communications\&.
.br 
Option groups: FD,SOCKET,IP4,IP6,RANGE 
.br 
Useful options:
bind,
range,
tcpwrap,
broadcast,
ip\-multicast\-loop,
ip\-multicast\-ttl,
ip\-multicast\-if,
ip\-add\-membership,
ttl,
tos,
sourceport,
pf
.br 
See also:
UDP4\-DATAGRAM,
UDP6\-DATAGRAM,
UDP\-SENDTO,
UDP\-RECVFROM,
UDP\-RECV,
UDP\-CONNECT,
UDP\-LISTEN,
IP\-DATAGRAM
.IP "\fB\f(CWUDP4\-DATAGRAM:<address>:<port>\fP\fP"
Like UDP\-DATAGRAM, but only supports IPv4
protocol (example1,
example2)\&.
.br 
Option groups: FD,SOCKET,IP4, RANGE
.IP "\fB\f(CWUDP6\-DATAGRAM:<address>:<port>\fP\fP"
Like UDP\-DATAGRAM, but only supports IPv6
protocol\&.
.br 
Option groups: FD,SOCKET,IP6,RANGE
.IP "\fB\f(CWUDP\-LISTEN:<port>\fP\fP"
Waits for a UDP/IP packet arriving on <port>
[UDP service] and `connects\(cq\& back to sender\&.
The accepted IP version is 4 or the one specified with option
pf\&.
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\&.
.br 
Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,IP6 
.br 
Useful options:
fork,
bind,
range,
pf 
.br 
See also:
UDP,
UDP4\-LISTEN,
UDP6\-LISTEN,
TCP\-LISTEN
.IP "\fB\f(CWUDP4\-LISTEN:<port>\fP\fP"
Like UDP\-LISTEN, but only support IPv4
protocol\&.
.br 
Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4 
.br 
.IP "\fB\f(CWUDP6\-LISTEN:<port>\fP\fP"
Like UDP\-LISTEN, but only support IPv6
protocol\&.
.br 
Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP6 
.br 
.IP "\fB\f(CWUDP\-SENDTO:<host>:<port>\fP\fP"
Communicates with the specified peer socket, defined by <port> [UDP
service] on
<host> [IP address], using UDP/IP version 4 or 6
depending on address specification, name resolution, or option
pf\&. 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\&.
.br 
Option groups: FD,SOCKET,IP4,IP6 
.br 
Useful options:
ttl,
tos,
bind,
sourceport,
pf
.br 
See also:
UDP4\-SENDTO,
UDP6\-SENDTO,
UDP\-RECVFROM,
UDP\-RECV,
UDP\-CONNECT,
UDP\-LISTEN,
IP\-SENDTO
.IP "\fB\f(CWUDP4\-SENDTO:<host>:<port>\fP\fP"
Like UDP\-SENDTO, but only supports IPv4
protocol\&.
.br 
Option groups: FD,SOCKET,IP4
.IP "\fB\f(CWUDP6\-SENDTO:<host>:<port>\fP\fP"
Like UDP\-SENDTO, but only supports IPv6
protocol\&.
.br 
Option groups: FD,SOCKET,IP6
.IP 
.IP "\fB\f(CWUDP\-RECVFROM:<port>\fP\fP"
Creates a UDP socket on <port> [UDP service] using
UDP/IP version 4 or 6 
depending on option pf\&.
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\&. This address works well with socat UDP\-SENDTO address peers\&.
.br 
Option groups: FD,SOCKET,IP4,IP6,CHILD,RANGE 
.br 
Useful options:
fork,
ttl,
tos,
bind,
sourceport,
pf
.br 
See also:
UDP4\-RECVFROM,
UDP6\-RECVFROM,
UDP\-SENDTO,
UDP\-RECV,
UDP\-CONNECT,
UDP\-LISTEN,
IP\-RECVFROM,
UNIX\-RECVFROM
.IP "\fB\f(CWUDP4\-RECVFROM:<port>\fP\fP"
Like UDP\-RECVFROM, but only supports IPv4 protocol\&.
.br 
Option groups: FD,SOCKET,IP4,CHILD,RANGE
.IP "\fB\f(CWUDP6\-RECVFROM:<port>\fP\fP"
Like UDP\-RECVFROM, but only supports IPv6 protocol\&.
.br 
Option groups: FD,SOCKET,IP6,CHILD,RANGE
.IP 
.IP "\fB\f(CWUDP\-RECV:<port>\fP\fP"
Creates a UDP socket on <port> [UDP service] using UDP/IP version 4 or 6
depending on option pf\&.
It receives packets from multiple unspecified peers and merges the data\&.
No replies are possible\&. It works well with, e\&.g\&., socat UDP\-SENDTO address peers; it behaves similar to a syslog server\&.
.br 
Option groups: FD,SOCKET,IP4,IP6,RANGE 
.br 
Useful options:
fork,
pf,
bind,
sourceport,
ttl,
tos
.br 
See also:
UDP4\-RECV,
UDP6\-RECV,
UDP\-SENDTO,
UDP\-RECVFROM,
UDP\-CONNECT,
UDP\-LISTEN,
IP\-RECV,
UNIX\-RECV
.IP "\fB\f(CWUDP4\-RECV:<port>\fP\fP"
Like UDP\-RECV, but only supports IPv4 protocol\&.
.br 
Option groups: FD,SOCKET,IP4,RANGE
.IP "\fB\f(CWUDP6\-RECV:<port>\fP\fP"
Like UDP\-RECV, but only supports IPv6 protocol\&.
.br 
Option groups: FD,SOCKET,IP6,RANGE
.IP 
.IP "\fB\f(CWUNIX\-CONNECT:<filename>\fP\fP"
Connects to <filename> assuming it is a UNIX domain
socket\&.
If <filename> does not exist, this is an error;
if <filename> is not a UNIX domain socket, this is an error;
if <filename> is a UNIX domain socket, but no process is listening, this is
an error\&.
.br 
Option groups: FD,SOCKET,NAMED,RETRY,UNIX 
.br 
)
Useful options:
bind
.br 
See also:
UNIX\-LISTEN,
UNIX\-SENDTO,
TCP
.IP 
.IP "\fB\f(CWUNIX\-LISTEN:<filename>\fP\fP"
Listens on <filename> using a UNIX domain stream
socket and accepts a connection\&.
If <filename> exists and is not a socket, this is an error\&.
If <filename> exists and is a UNIX domain socket, binding to the address
fails (use option unlink\-early!)\&.
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 unlink\-close) (example)\&.
.br 
Option groups: FD,SOCKET,NAMED,LISTEN,CHILD,RETRY,UNIX 
.br 
Useful options:
fork,
umask,
mode,
user,
group,
unlink\-early
.br 
See also:
UNIX\-CONNECT,
UNIX\-RECVFROM,
UNIX\-RECV,
TCP\-LISTEN
.IP 
.IP "\fB\f(CWUNIX\-SENDTO:<filename>\fP\fP"
Communicates with the specified peer socket, defined by [<filename>] 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 neccessary to bind the
local socket to an address (e\&.g\&. \f(CW/tmp/sock1\fP, which must not exist
before)\&.
This address type works well with socat UNIX\-RECVFROM and UNIX\-RECV address
peers\&.
.br 
Option groups: FD,SOCKET,NAMED,UNIX
.br 
Useful options:
bind
.br 
See also:
UNIX\-RECVFROM,
UNIX\-RECV,
UNIX\-CONNECT,
UDP\-SENDTO,
IP\-SENDTO
.IP 
.IP "\fB\f(CWUNIX\-RECVFROM:<filename>\fP\fP"
Creates a UNIX domain datagram socket [<filename>]\&.
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\&.
.br 
Option groups: FD,SOCKET,NAMED,CHILD,UNIX 
.br 
Useful options:
fork
.br 
See also:
UNIX\-SENDTO,
UNIX\-RECV,
UNIX\-LISTEN,
UDP\-RECVFROM,
IP\-RECVFROM
.IP 
.IP "\fB\f(CWUNIX\-RECV:<filename>\fP\fP"
Creates a UNIX domain datagram socket [<filename>]\&.
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: FD,SOCKET,NAMED,UNIX 
.br 
See also:
UNIX\-SENDTO,
UNIX\-RECVFROM,
UNIX\-LISTEN,
UDP\-RECV,
IP\-RECV
.IP 
.IP "\fB\f(CWUNIX\-CLIENT:<filename>\fP\fP"
Communicates with the specified peer socket, defined by
[<filename>] 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\&.
.br 
Option groups: FD,SOCKET,NAMED,UNIX 
.br 
Useful options:
bind
.br 
See also:
UNIX\-CONNECT,
UNIX\-SENDTO,
GOPEN
.IP 
.IP "\fB\f(CWABSTRACT\-CONNECT:<string>\fP\fP"
.IP "\fB\f(CWABSTRACT\-LISTEN:<string>\fP\fP"
.IP "\fB\f(CWABSTRACT\-SENDTO:<string>\fP\fP"
.IP "\fB\f(CWABSTRACT\-RECVFROM:<string>\fP\fP"
.IP "\fB\f(CWABSTRACT\-RECV:<string>\fP\fP"
.IP "\fB\f(CWABSTRACT\-CLIENT:<string>\fP\fP"
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 archieve this the socket address strings are
prefixed with \(dq\&\e0\(dq\& 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\&.

.PP 
.SH "ADDRESS OPTIONS"

.PP 
Address options can be applied to address specifications to influence the
process of opening the addresses and the 
properties of the resulting data channels\&. 
.PP 
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 \fIoption groups\fP 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 option \-g)\&.
.PP 
Address options have data types that their values must conform to\&. 
Every address option consists of just a keyword or a keyword followed by
\(dq\&=value\(dq\&, where value must conform to the options type\&.
Some address options manipulate parameters of system calls;
e\&.g\&., option sync sets the 
\f(CWO_SYNC\fP
flag with the 
\f(CWopen()\fP
call\&. 
Other options cause a system or library call; e\&.g\&., with option `ttl=value\(cq\&
the 
\f(CWsetsockopt(fd, SOL_IP, IP_TTL, value, sizeof(int))\fP
call is applied\&.
Other
options set internal \fBsocat\fP variables that are used during data transfer;
e\&.g\&., `crnl\(cq\& 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 
\f(CWchroot()\fP
call\&.
.PP 
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, \fBsocat\fP has
built in an \fIoption phase\fP 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\&.
.PP 
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 
\f(CWsetsockopt()\fP
cause multiple
invocations\&. With options that set parameters for a required call like
\f(CWopen()\fP
or set internal flags, the value of the last option occurrence is effective\&.
.PP 
The existence or semantics of many options are system dependent\&. \fBSocat\fP
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\&.
.PP 
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 \fBxio\&.help\fP\&. 
.br 
.br 

.PP 
.br 

.PP 
\fI\fBFD option group\fP\fP
.PP 
This option group contains options that are applied to a UN*X
style file descriptor, no matter how it was generated\&.
Because all current \fBsocat\fP address types are file descriptor based, these
options may be applied to any address\&. 
.br 
Note: Some of these options are also member of another option group, that
provides an other, 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\&.
.IP "\fB\f(CWcloexec=<bool>\fP\fP"
Sets the 
\f(CWFD_CLOEXEC\fP
flag with the 
\f(CWfcntl()\fP
system call to value
<bool>\&. If set,
the file descriptor is closed on 
\f(CWexec()\fP
family function calls\&. \fBSocat\fP
internally handles 
this flag for the fds it controls, so in most cases there will be no need to
apply this option\&. 
.IP "\fB\f(CWsetlk\fP\fP"
Tries to set a discretionary write lock to the whole file using the 
\f(CWfcntl(fd,
F_SETLK, \&.\&.\&.)\fP
system call\&. If the file is already locked, this call results
in an error\&. 
On Linux, when the file permissions for group are \(dq\&S\(dq\& (g\-x,g+s), and the
file system is locally mounted with the \(dq\&mand\(dq\& option, the lock is
mandatory, i\&.e\&. prevents other processes from opening the file\&.
.IP "\fB\f(CWsetlkw\fP\fP"
Tries to set a discretionary waiting write lock to the whole file using the
\f(CWfcntl(fd, F_SETLKW, \&.\&.\&.)\fP
system call\&. If the file is already locked,
this call blocks\&. 
See option setlk for information about making this
lock mandatory\&. 
.IP "\fB\f(CWsetlk\-rd\fP\fP"
Tries to set a discretionary read lock to the whole file using the 
\f(CWfcntl(fd,
F_SETLK, \&.\&.\&.)\fP
system call\&. If the file is already write locked, this call
results in an error\&. 
See option setlk for information about making this
lock mandatory\&. 
.IP "\fB\f(CWsetlkw\-rd\fP\fP"
Tries to set a discretionary waiting read lock to the whole file using the
\f(CWfcntl(fd, F_SETLKW, \&.\&.\&.)\fP
system call\&. If the file is already write
locked, this call blocks\&. 
See option setlk for information about making this
lock mandatory\&. 
.IP "\fB\f(CWflock\-ex\fP\fP"
Tries to set a blocking exclusive advisory lock to the file using the
\f(CWflock(fd, LOCK_EX)\fP
system call\&. \fBSocat\fP hangs in this call if the file
is locked by another process\&.
.IP "\fB\f(CWflock\-ex\-nb\fP\fP"
Tries to set a nonblocking exclusive advisory lock to the file using the
\f(CWflock(fd, LOCK_EX|LOCK_NB)\fP
system call\&. If the file is already locked,
this option results in an error\&.
.IP "\fB\f(CWflock\-sh\fP\fP"
Tries to set a blocking shared advisory lock to the file using the
\f(CWflock(fd, LOCK_SH)\fP
system call\&. \fBSocat\fP hangs in this call if the file
is locked by another process\&.
.IP "\fB\f(CWflock\-sh\-nb\fP\fP"
Tries to set a nonblocking shared advisory lock to the file using the
\f(CWflock(fd, LOCK_SH|LOCK_NB)\fP
system call\&. If the file is already locked,
this option results in an error\&.
.IP "\fB\f(CWlock\fP\fP"
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\&.
.IP "\fB\f(CWuser=<user>\fP\fP"
Sets the <user> (owner) of the stream\&.
If the address is member of the NAMED option group,
\fBsocat\fP uses the 
\f(CWchown()\fP
system call after opening the
file or binding to the UNIX domain socket (race condition!)\&.
Without filesystem entry, \fBsocat\fP sets the user of the stream 
using the 
\f(CWfchown()\fP
system call\&.
These calls might require root privilege\&. 
.IP "\fB\f(CWuser\-late=<user>\fP\fP"
Sets the owner of the fd to <user> with the 
\f(CWfchown()\fP
system call after opening 
or connecting the channel\&.
This is useful only on file system entries\&.
.IP "\fB\f(CWgroup=<group>\fP\fP"
Sets the <group> of the stream\&.
If the address is member of the NAMED option group,
\fBsocat\fP uses the 
\f(CWchown()\fP
system call after opening the
file or binding to the UNIX domain socket (race condition!)\&.
Without filesystem entry, \fBsocat\fP sets the group of the stream 
with the 
\f(CWfchown()\fP
system call\&. 
These calls might require group membership or root privilege\&. 
.IP "\fB\f(CWgroup\-late=<group>\fP\fP"
Sets the group of the fd to <group> with the
\f(CWfchown()\fP
system call after opening 
or connecting the channel\&.
This is useful only on file system entries\&. 
.IP "\fB\f(CWmode=<mode>\fP\fP"
Sets the <mode> [mode_t] (permissions) of the stream\&.
If the address is member of the NAMED option group and
uses the 
\f(CWopen()\fP
or 
\f(CWcreat()\fP
call, the mode is applied with these\&.
If the address is member of the NAMED option group with…