socat/doc/socat.1

.TH "socat" "1" "March 2007" "socat" "" 
.PP 
.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\&. 
It might be one of the tools that one `has already needed\'\&.
.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\' 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 "daemon"\&. 
.IP "\fB\f(CW-lf\fP\fP\f(CW <logfile>\fP" 
Writes messages to <logfile> [filename] instead of
stderr\&. 
.IP "\fB\f(CW-ls\fP\fP" 
Writes messages to stderr (this is the default)\&.
.IP "\fB\f(CW-lp\fP\fP\f(CW<progname>\fP" 
Overrides the program name printed in error messages\&.
.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 "daemon"\&. 
.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 "> " or "< " 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 "> " or "< "
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 intervall 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\'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 \':\' from the keyword and
from each 
other, and zero or more address options separated by \',\'\&. 
.PP 
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\&. 
.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 \'=\'\&. 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 "!!" 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 ( { [ \' 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 \e or within ""
.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\&.
<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 \'/\', the part after the last \'/\' 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 procotol 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
See also:
IP4-SENDTO,
IP6-SENDTO,
IP-RECVFROM,
IP-RECV,
UDP-SENDTO
UNIX-SENDTO
.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
eventual 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:
range,
tcpwrap,
broadcast,
ip-multicast-loop,
ip-multicast-ttl,
ip-multicast-if,
ip-add-membership,
ttl,
tos,
bind,
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 procotol 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\&.
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 procotol 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\'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,
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\'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,
fork,
bind,
range,
tcpwrap,
su,
reuseaddr,
retry
.br 
See also:
OPENSSL,
TCP
.IP "\fB\f(CWPIPE:<filename>\fP\fP" 
If <filename> already exists, it is opened\&.
If is 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\'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(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 \',\' or "!!", 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,
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
pf\&.
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,
backlog,
mss,
su,
reuseaddr,
retry,
retry
.br 
See also:
TCP4-LISTEN,
TCP6-LISTEN,
UDP-LISTEN,
UNIX-LISTEN,
OPENSSL-LISTEN
.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 assignes to it the address and netmask
defined by the parameters\&. The resulting network interface is ready for use
by other processes; socat serves its "wire side"\&. This address requires read
and write access to the tunnel cloning device, usually \f(CW/dev/net/tun\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\' 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
eventual 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:
range,
tcpwrap,
broadcast,
ip-multicast-loop,
ip-multicast-ttl,
ip-multicast-if,
ip-add-membership,
ttl,
tos,
bind,
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\' 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 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\&.
It 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 "\e0" 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
"=value", 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\'
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\' 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 "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\&.
.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 without using these
system calls, \fBsocat\fP uses the \f(CWchmod()\fP system call after opening the
filesystem entry or binding to the UNIX domain socket (race condition!)\&.
Otherwise, \fBsocat\fP sets the mode of the stream
using \f(CWfchmod()\fP\&. 
These calls might require ownership or root privilege\&.
.IP "\fB\f(CWperm-late=<mode>\fP\fP" 
Sets the permissions of the fd to value <mode>
[mode_t] using the \f(CWfchmod()\fP system call after
opening or connecting the channel\&.
This is useful only on file system entries\&. 
.IP "\fB\f(CWappend=<bool>\fP\fP" 
Always writes data to the actual end of file\&.
If the address is member of the OPEN option group, 
\fBsocat\fP uses the \f(CWO_APPEND\fP flag with the \f(CWopen()\fP system call
(example)\&.
Otherwise, \fBsocat\fP applies the \f(CWfcntl(fd, F_SETFL, O_APPEND)\fP call\&.
.IP "\fB\f(CWnonblock=<bool>\fP\fP" 
Tries to open or use file in nonblocking mode\&. Its only effects are that the
\f(CWconnect()\fP 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,
\fBsocat\fP uses the \f(CWO_NONBLOCK\fP flag with the \f(CWopen()\fP system call\&.
Otherwise, \fBsocat\fP applies the \f(CWfcntl(fd, F_SETFL, O_NONBLOCK)\fP call\&.
.IP "\fB\f(CWbinary\fP\fP" 
Opens the file in binary mode to avoid implicit line terminator
conversions (Cygwin)\&.
.IP "\fB\f(CWtext\fP\fP" 
Opens the file in text mode to force implicit line terminator conversions
(Cygwin)\&.
.IP "\fB\f(CWnoinherit\fP\fP" 
Does not keep this file open in a spawned process (Cygwin)\&.
.IP "\fB\f(CWcool-write\fP\fP" 
Takes it easy when write fails with EPIPE or ECONNRESET and logs the message
with \fInotice\fP level instead of \fIerror\fP\&.
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\&.
.br 
This option is experimental\&.
.IP "\fB\f(CWend-close\fP\fP" 
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 (example)\&.
.br 
Normally, socket connections will be ended with \f(CWshutdown(2)\fP which
terminates the socket even if it is shared by multiple processes\&. 
\f(CWclose(2)\fP "unlinks" the socket from the process but keeps it active as
long as there are still links from other processes\&.
.br 
Similarly, when an address of type EXEC or SYSTEM is ended, socat usually
will explicitely kill the sub process\&. With this option, it will just close
the file descriptors\&.
.PP 
.br 
.PP 
\fI\fBNAMED option group\fP\fP
.PP 
These options work on file system entries\&.
.br 
See also options user, group, and
mode\&.
.PP 
.IP "\fB\f(CWuser-early=<user>\fP\fP" 
Changes the <user> (owner) of the file system entry before
accessing it, using the 
\f(CWchown()\fP system call\&. This call might require root privilege\&.
.IP "\fB\f(CWgroup-early=<group>\fP\fP" 
Changes the <group> of the file system entry before
accessing it, using the 
\f(CWchown()\fP system call\&. This call might require group membership or root
privilege\&. 
.IP "\fB\f(CWperm-early=<mode>\fP\fP" 
Changes the <mode> [mode_t] of the file system entry
before accessing it, using the 
\f(CWchmod()\fP system call\&. This call might require ownership or root
privilege\&. 
.IP "\fB\f(CWumask=<mode>\fP\fP" 
Sets the umask of the process to <mode> [mode_t] before
accessing the file system entry (useful 
with UNIX domain sockets!)\&. This call might affect all further operations
of the \fBsocat\fP process!  
.IP "\fB\f(CWunlink-early\fP\fP" 
Unlinks (removes) the file before opening it and even before applying
user-early etc\&. 
.IP "\fB\f(CWunlink\fP\fP" 
Unlinks (removes) the file before accessing it, but after user-early etc\&.
.IP "\fB\f(CWunlink-late\fP\fP" 
Unlinks (removes) the file after opening it to make it inaccessible for
other processes after a short race condition\&. 
.IP "\fB\f(CWunlink-close\fP\fP" 
Removes the addresses file system entry when closing the address\&.
For named pipes,
listening unix domain sockets,
and the symbolic links of pty addresses,
the default is 1; for created files,
opened files,
generic opened files, and
client unix domain sockets the default is 0\&.
.PP 
.br 
.PP 
\fI\fBOPEN option group\fP\fP
.PP 
The OPEN group options allow to set flags with the \f(CWopen()\fP system call\&. 
E\&.g\&., option `creat\' sets the \f(CWO_CREAT\fP flag\&.
.br 
See also options append and
nonblock\&.
.IP "\fB\f(CWcreat=<bool>\fP\fP" 
Creates the file if it does not exist (example)\&.
.IP "\fB\f(CWdsync=<bool>\fP\fP" 
Blocks \f(CWwrite()\fP calls until metainfo is physically written to media\&.
.IP "\fB\f(CWexcl=<bool>\fP\fP" 
With option creat, if file exists this is an error\&.
.IP "\fB\f(CWlargefile=<bool>\fP\fP" 
On 32 bit systems, allows a file larger than 2^31 bytes\&.
.IP "\fB\f(CWnoatime\fP\fP" 
Sets the O_NOATIME options, so reads do not change the access timestamp\&.
.IP "\fB\f(CWnoctty=<bool>\fP\fP" 
Does not make this file the controlling terminal\&.
.IP "\fB\f(CWnofollow=<bool>\fP\fP" 
Does not follow symbolic links\&.
.IP "\fB\f(CWnshare=<bool>\fP\fP" 
Does not allow to share this file with other processes\&.
.IP "\fB\f(CWrshare=<bool>\fP\fP" 
Does not allow other processes to open this file for writing\&.
.IP "\fB\f(CWrsync=<bool>\fP\fP" 
Blocks \f(CWwrite()\fP until metainfo is physically written to media\&.
.IP "\fB\f(CWsync=<bool>\fP\fP" 
Blocks \f(CWwrite()\fP until data is physically written to media\&.
.IP "\fB\f(CWrdonly=<bool>\fP\fP" 
Opens the file for reading only\&.
.IP "\fB\f(CWwronly=<bool>\fP\fP" 
Opens the file for writing only\&.
.IP "\fB\f(CWtrunc\fP\fP" 
Truncates the file to size 0 during opening it\&.
.PP 
.br 
.PP 
\fI\fBREG and BLK option group\fP\fP
.PP 
These options are usually applied to a UN*X file descriptor, but their
semantics make sense only on a file supporting random access\&.
.IP "\fB\f(CWseek=<offset>\fP\fP" 
Applies the \f(CWlseek(fd, <offset>, SEEK_SET)\fP (or \f(CWlseek64\fP) system
call, thus positioning the file pointer absolutely to <offset>
[off_t or off64_t]\&.
.IP "\fB\f(CWseek-cur=<offset>\fP\fP" 
Applies the \f(CWlseek(fd, <offset>, SEEK_CUR)\fP (or \f(CWlseek64\fP) system
call, thus positioning the file pointer <offset> [off_t or
off64_t] bytes relatively to its current position (which
is usually 0)\&.
.IP "\fB\f(CWseek-end=<offset>\fP\fP" 
Applies the \f(CWlseek(fd, <offset>, SEEK_END)\fP (or \f(CWlseek64\fP) system
call, thus positioning the file pointer <offset> [off_t or
off64_t] bytes relatively to the files current end\&.  
.IP "\fB\f(CWftruncate=<offset>\fP\fP" 
Applies the \f(CWftruncate(fd, <offset>)\fP
(or \f(CWftruncate64\fP if available) system call, thus
truncating the file at the position <offset> [off_t or 
off64_t]\&.
.IP 
.IP "\fB\f(CWsecrm=<bool>\fP\fP" 
.IP "\fB\f(CWunrm=<bool>\fP\fP" 
.IP "\fB\f(CWcompr=<bool>\fP\fP" 
.IP "\fB\f(CWext2-sync=<bool>\fP\fP" 
.IP "\fB\f(CWimmutable=<bool>\fP\fP" 
.IP "\fB\f(CWext2-append=<bool>\fP\fP" 
.IP "\fB\f(CWnodump=<bool>\fP\fP" 
.IP "\fB\f(CWext2-noatime=<bool>\fP\fP" 
.IP "\fB\f(CWjournal-data=<bool>\fP\fP" 
.IP "\fB\f(CWnotail=<bool>\fP\fP" 
.IP "\fB\f(CWdirsync=<bool>\fP\fP" 
These options change non standard file attributes on operating systems and
file systems that support these features, like Linux with ext2fs,
ext3fs, 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\&.
.PP 
.br 
.PP 
\fI\fBPROCESS option group\fP\fP
.PP 
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\&.
.IP "\fB\f(CWchroot=<directory>\fP\fP" 
Performs a \f(CWchroot()\fP operation to <directory>
after processing the address (example)\&. This call might require root privilege\&.
.IP "\fB\f(CWchroot-early=<directory>\fP\fP" 
Performs a \f(CWchroot()\fP operation to <directory>
before opening the address\&. This call might require root privilege\&.
.IP "\fB\f(CWsetgid=<group>\fP\fP" 
Changes the primary <group> of the process after
processing the address\&. This call might require root privilege\&.
.IP "\fB\f(CWsetgid-early=<group>\fP\fP" 
Changes the primary <group> of the process before opening
the address\&. This call might require root privilege\&.
.IP "\fB\f(CWsetuid=<user>\fP\fP" 
Changes the <user> (owner) of the process after processing
the address\&. This call might require root privilege\&.
.IP "\fB\f(CWsetuid-early=<user>\fP\fP" 
Changes the <user> (owner) of the process before opening
the address\&. This call might require root privilege\&. 
.IP "\fB\f(CWsu=<user>\fP\fP" 
Changes the <user> (owner) and groups of the process after
processing the address (example)\&. This call might require root privilege\&. 
.IP "\fB\f(CWsu-d=<user>\fP\fP" 
Short name for \fB\f(CWsubstuser-delayed\fP\fP\&. 
Changes the <user>
(owner) and groups of the process after processing the address (example)\&.
The user and his groups are retrieved \fIbefore\fP a possible
\f(CWchroot()\fP\&. This call might require root privilege\&. 
.IP "\fB\f(CWsetpgid=<pid_t>\fP\fP" 
Makes the process a member of the specified process group
<pid_t>\&. If no value 
is given, or if the value is 0 or 1, the process becomes leader of a new
process group\&. 
.IP "\fB\f(CWsetsid\fP\fP" 
Makes the process the leader of a new session (example)\&.
.PP 
.br 
.PP 
\fI\fBREADLINE option group\fP\fP
.PP 
These options apply to the readline address type\&.
.IP "\fB\f(CWhistory=<filename>\fP\fP" 
Reads and writes history from/to <filename> (example)\&.
.IP "\fB\f(CWnoprompt\fP\fP" 
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\&. 
.IP "\fB\f(CWnoecho=<pattern>\fP\fP" 
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\&.
(example)
.IP "\fB\f(CWprompt=<string>\fP\fP" 
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 archieved\&.
.PP 
.br 
.PP 
\fI\fBAPPLICATION option group\fP\fP
.PP 
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
PROXY\&.
.IP "\fB\f(CWcr\fP\fP" 
Converts the default line termination character NL (\'\en\', 0x0a) to/from CR
(\'\er\', 0x0d) when writing/reading on this channel\&. 
.IP "\fB\f(CWcrnl\fP\fP" 
Converts the default line termination character NL (\'\en\', 0x0a) to/from CRNL
("\er\en", 0x0d0a) when writing/reading on this channel (example)\&.
Note: socat simply strips all CR characters\&.
.IP "\fB\f(CWignoreeof\fP\fP" 
When EOF occurs on this channel, \fBsocat\fP ignores it and tries to read more
data (like "tail -f") (example)\&.
.IP "\fB\f(CWreadbytes=<bytes>\fP\fP" 
\fBsocat\fP 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\&.
.IP "\fB\f(CWlockfile=<filename>\fP\fP" 
If lockfile exists, exits with error\&. If lockfile does not exist, creates it
and continues, unlinks lockfile on exit\&.
.IP "\fB\f(CWwaitlock=<filename>\fP\fP" 
If lockfile exists, waits until it disappears\&. When lockfile does not exist,
creates it and continues, unlinks lockfile on exit\&.
.PP 
.br 
.PP 
\fI\fBSOCKET option group\fP\fP
.PP 
These options are intended for all kinds of sockets, e\&.g\&. IP or UNIX domain\&. Most are applied with a \f(CWsetsockopt()\fP call\&.
.IP "\fB\f(CWbind=<sockname>\fP\fP" 
Binds the socket to the given socket address using the \f(CWbind()\fP system
call\&. The form of <sockname> is socket domain dependent:
IP4 and IP6 allow the form [hostname|hostaddress][:(service|port)] (example),
UNIX domain sockets require <filename>\&. 
.IP "\fB\f(CWconnect-timeout=<seconds>\fP\fP" 
Abort the connection attempt after <seconds> [timeval]
with error status\&.
.IP "\fB\f(CWinterface=<interface>\fP\fP" 
Binds the socket to the given <interface>\&.
This option might require root privilege\&.
.IP "\fB\f(CWbroadcast\fP\fP" 
For datagram sockets, allows sending to broadcast addresses and receiving
packets addressed to broadcast addresses\&. 
.IP "\fB\f(CWbsdcompat\fP\fP" 
Emulates some (old?) bugs of the BSD socket implementation\&.
.IP "\fB\f(CWdebug\fP\fP" 
Enables socket debugging\&.
.IP "\fB\f(CWdontroute\fP\fP" 
Only communicates with directly connected peers, does not use routers\&.
.IP "\fB\f(CWkeepalive\fP\fP" 
Enables sending keepalives on the socket\&.
.IP "\fB\f(CWlinger=<seconds>\fP\fP" 
Blocks \f(CWshutdown()\fP or \f(CWclose()\fP until data transfers have finished
or the given timeout [int] expired\&. 
.IP "\fB\f(CWoobinline\fP\fP" 
Places out-of-band data in the input data stream\&.
.IP "\fB\f(CWpriority=<priority>\fP\fP" 
Sets the protocol defined <priority> [<int>] for outgoing
packets\&. 
.IP "\fB\f(CWrcvbuf=<bytes>\fP\fP" 
Sets the size of the receive buffer after the \f(CWsocket()\fP call to
<bytes> [int]\&.  With TCP
sockets, this value corresponds to the socket\'s maximal window size\&.
.IP "\fB\f(CWrcvbuf-late=<bytes>\fP\fP" 
Sets the size of the receive buffer when the socket is already
connected to <bytes> [int]\&. 
With TCP sockets, this value corresponds to the socket\'s 
maximal window size\&. 
.IP "\fB\f(CWrcvlowat=<bytes>\fP\fP" 
Specifies the minimum number of received bytes [int] until
the socket layer will pass the buffered data to \fBsocat\fP\&. 
.IP "\fB\f(CWrcvtimeo=<seconds>\fP\fP" 
Sets the receive timeout [timeval]\&. 
.IP "\fB\f(CWreuseaddr\fP\fP" 
Allows other sockets to bind to an address even if parts of it (e\&.g\&. the
local port) are already in use by \fBsocat\fP (example)\&. 
.IP "\fB\f(CWsndbuf=<bytes>\fP\fP" 
Sets the size of the send buffer after the \f(CWsocket()\fP call to
<bytes> [int]\&.
.IP "\fB\f(CWsndbuf-late=<bytes>\fP\fP" 
Sets the size of the send buffer when the socket is connected to
<bytes> [int]\&.
.IP "\fB\f(CWsndlowat=<bytes>\fP\fP" 
Specifies the minimum number of bytes in the send buffer until the socket
layer will send the data to <bytes> [int]\&.
.IP "\fB\f(CWsndtimeo=<seconds>\fP\fP" 
Sets the send timeout to seconds [timeval]\&.
.IP "\fB\f(CWtype=<type>\fP\fP" 
Sets the type of the socket, usually as argument to the \f(CWsocket()\fP or
\f(CWsocketpair()\fP call, to <type> [int]\&.
Under Linux, 1 means stream oriented socket, 2 means datagram socket, and 3
means raw socket\&.
.IP "\fB\f(CWpf=<string>\fP\fP" 
Forces the use of the specified IP version\&. <string> can be
something like "ip4" or "ip6"\&.
.PP 
.br 
.PP 
\fI\fBUNIX option group\fP\fP
.PP 
These options apply to UNIX domain based addresses\&.
.IP "\fB\f(CWunix-tightsocklen=[0|1]\fP\fP" 
On socket operations, pass a socket address length that does not include the
whole \f(CWstruct sockaddr_un\fP record but (besides other components) only
the relevant part of the filename or abstract string\&. Default is 1\&.
.PP 
\fI\fBIP4 and IP6 option groups\fP\fP
.PP 
These options can be used with IPv4 and IPv6 based sockets\&.
.IP "\fB\f(CWtos=<tos>\fP\fP" 
Sets the TOS (type of service) field of outgoing packets to <tos>
[byte] (see RFC 791)\&.
.IP "\fB\f(CWttl=<ttl>\fP\fP" 
Sets the TTL (time to live) field of outgoing packets to <ttl>
[byte]\&.
.IP "\fB\f(CWipoptions=<data>\fP\fP" 
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 \f(CWipoptions=x8307040a000001\fP\&.
.br 
IP options are defined in RFC 791\&. 
.br 
.IP "\fB\f(CWmtudiscover=<0|1|2>\fP\fP" 
Takes 0, 1, 2 to never, want, or always use path MTU discover on this
socket\&. 
.IP "\fB\f(CWip-add-membership=<multicast-address:interface-address>\fP\fP" 
.IP "\fB\f(CWip-add-membership=<multicast-address:interface-name>\fP\fP" 
.IP "\fB\f(CWip-add-membership=<multicast-address:interface-index>\fP\fP" 
.IP "\fB\f(CWip-add-membership=<multicast-address:interface-address:interface-name>\fP\fP" 
.IP "\fB\f(CWip-add-membership=<multicast-address:interface-address:interface-index>\fP\fP" 
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 \f(CWstruct mreqn\fP (Linux)\&.
.br 
The indices of active network interfaces can be shown using the utility
\fBprocan\fP\&.
dif(\fB\f(CWip-multicast-if=<hostname>\fP\fP)
Specifies hostname or address of the network interface to be used for
multicast traffic\&.
dif(\fB\f(CWip-multicast-loop=<bool>\fP\fP)
Specifies if outgoing multicast traffic should loop back to the interface\&.
dif(\fB\f(CWip-multicast-ttl=<byte>\fP\fP)
Sets the TTL used for outgoing multicast traffic\&. Default is 1\&.
.IP "\fB\f(CWres-debug\fP\fP" 
.IP "\fB\f(CWres-aaonly\fP\fP" 
.IP "\fB\f(CWres-usevc\fP\fP" 
.IP "\fB\f(CWres-primary\fP\fP" 
.IP "\fB\f(CWres-igntc\fP\fP" 
.IP "\fB\f(CWres-recurse\fP\fP" 
.IP "\fB\f(CWres-defnames\fP\fP" 
.IP "\fB\f(CWres-stayopen\fP\fP" 
.IP "\fB\f(CWres-dnsrch\fP\fP" 
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\&.
.IP 
.PP 
.br 
.PP 
\fI\fBIP6 option group\fP\fP
.PP 
These options can only be used on IPv6 based sockets\&. See IP
options for options that can be applied to both IPv4 and IPv6
sockets\&.
.IP "\fB\f(CWipv6only=<bool>\fP\fP" 
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\&.
.PP 
.br 
.PP 
\fI\fBTCP option group\fP\fP
.PP 
These options may be applied to TCP sockets\&. They work by invoking \f(CWsetsockopt()\fP with the appropriate parameters\&.
.IP "\fB\f(CWcork\fP\fP" 
Doesn\'t send packets smaller than MSS (maximal segment size)\&.
.IP "\fB\f(CWdefer-accept\fP\fP" 
While listening, accepts connections only when data from the peer arrived\&.
.IP "\fB\f(CWkeepcnt=<count>\fP\fP" 
Sets the number of keepalives before shutting down the socket to
<count> [int]\&.
.IP "\fB\f(CWkeepidle=<seconds>\fP\fP" 
Sets the idle time before sending the first keepalive to <seconds>
[int]\&.
.IP "\fB\f(CWkeepintvl=<seconds>\fP\fP" 
Sets the intervall between two keepalives to <seconds>
[int]\&. 
.IP "\fB\f(CWlinger2=<seconds>\fP\fP" 
Sets the time to keep the socket in FIN-WAIT-2 state to <seconds>
[int]\&.
.IP "\fB\f(CWmss=<bytes>\fP\fP" 
Sets the MSS (maximum segment size) after the \f(CWsocket()\fP call to <bytes>
[int]\&. This
value is then proposed to the peer with the SYN or SYN/ACK packet
(example)\&. 
.IP "\fB\f(CWmss-late=<bytes>\fP\fP" 
Sets the MSS of the socket after connection has been established to <bytes>
[int]\&.
.IP "\fB\f(CWnodelay\fP\fP" 
Turns off the Nagle algorithm for measuring the RTT (round trip time)\&.
.IP "\fB\f(CWrfc1323\fP\fP" 
Enables RFC1323 TCP options: TCP window scale, round-trip time measurement
(RTTM), and protect against wrapped sequence numbers (PAWS) (AIX)\&.
.IP "\fB\f(CWstdurg\fP\fP" 
Enables RFC1122 compliant urgent pointer handling (AIX)\&.
.IP "\fB\f(CWsyncnt=<count>\fP\fP" 
Sets the maximal number of SYN retransmits during connect to <count>
[int]\&.
.IP "\fB\f(CWmd5sig\fP\fP" 
Enables generation of MD5 digests on the packets (FreeBSD)\&.
.IP "\fB\f(CWnoopt\fP\fP" 
Disables use of TCP options (FreeBSD, MacOSX)\&.
.IP "\fB\f(CWnopush\fP\fP" 
sets the TCP_NOPUSH socket option (FreeBSD, MacOSX)\&.
.IP "\fB\f(CWsack-disable\fP\fP" 
Disables use the selective acknowledge feature (OpenBSD)\&.
.IP "\fB\f(CWsignature-enable\fP\fP" 
Enables generation of MD5 digests on the packets (OpenBSD)\&.
.IP "\fB\f(CWabort-threshold=<milliseconds>\fP\fP" 
Sets the time to wait for an answer of the peer on an established connection
(HP-UX)\&.
.IP "\fB\f(CWconn-abort-threshold=<milliseconds>\fP\fP" 
Sets the time to wait for an answer of the server during the initial connect
(HP-UX)\&.
.IP "\fB\f(CWkeepinit\fP\fP" 
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)\&.
.IP "\fB\f(CWpaws\fP\fP" 
Enables the "protect against wrapped sequence numbers" feature (Tru64)\&.
.IP "\fB\f(CWsackena\fP\fP" 
Enables selective acknowledge (Tru64)\&.
.IP "\fB\f(CWtsoptena\fP\fP" 
Enables the time stamp option that allows RTT recalculation on existing
connections (Tru64)\&.
.PP 
.br 
.PP 
\fI\fBUDP and TCP option groups\fP\fP
.PP 
Here we find options that are related to the network port mechanism and that
thus can be used with UDP and TCP, client and server addresses\&.
.IP "\fB\f(CWsourceport=<port>\fP\fP" 
For outgoing (client) TCP and UDP connections, it sets the source
<port> using an extra \f(CWbind()\fP call\&.
With TCP or UDP listen addresses, socat immediately shuts down the
connection if the client does not use this sourceport (example)\&.
.IP "\fB\f(CWlowport\fP\fP" 
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 <= 1023\&.
This mechanism can provide limited authorization under some circumstances\&.
.PP 
.br 
.PP 
\fI\fBSOCKS option group\fP\fP
.PP 
When using SOCKS type addresses, some socks specific options can be set\&.
.IP "\fB\f(CWsocksport=<tcp service>\fP\fP" 
Overrides the default "socks" service or port 1080 for the socks server
port with <TCP service>\&.
.IP "\fB\f(CWsocksuser=<user>\fP\fP" 
Sends the <user> [string] in the username field to the
socks server\&. Default is the actual user name ($LOGNAME or $USER) (example)\&.
.PP 
.br 
.PP 
\fI\fBHTTP option group\fP\fP
.PP 
Options that can be provided with HTTP type addresses\&. The only HTTP address
currently implemented is proxy-connect\&.
.PP 
.IP "\fB\f(CWproxyport=<TCP service>\fP\fP" 
Overrides the default HTTP proxy port 8080 with
<TCP service>\&.
.IP "\fB\f(CWignorecr\fP\fP" 
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\&.
.IP "\fB\f(CWproxyauth=<username>:<password>\fP\fP" 
Provide "basic" authentication to the proxy server\&. The argument to the
option is used with a "Proxy-Authorization: Base" header in base64 encoded
form\&.
.br 
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\&.
.IP "\fB\f(CWresolve\fP\fP" 
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\&.
.PP 
.br 
.PP 
\fI\fBRANGE option group\fP\fP
.PP 
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\&.
.IP "\fB\f(CWrange=<address-range>\fP\fP" 
After accepting a connection, tests if the peer is within \fIrange\fP\&. 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 (example); for IPv6, it is [ip6-address/bits], e\&.g\&. [::1/128]\&.
If the client address does not match, \fBsocat\fP issues a warning and keeps
listening/receiving\&.
.IP "\fB\f(CWtcpwrap[=<name>]\fP\fP" 
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 <name> (type string)
is passed to the wrapper functions as daemon process name (example)\&. 
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\&.
.IP "\fB\f(CWallow-table=<filename>\fP\fP" 
Takes the specified file instead of /etc/hosts\&.allow\&.
.IP "\fB\f(CWdeny-table=<filename>\fP\fP" 
Takes the specified file instead of /etc/hosts\&.deny\&.
.IP "\fB\f(CWtcpwrap-etc=<directoryname>\fP\fP" 
Looks for hosts\&.allow and hosts\&.deny in the specified directory\&. Is
overridden by options hosts-allow
and hosts-deny\&.
.PP 
.br 
.PP 
\fI\fBLISTEN option group\fP\fP
.PP 
Options specific to listening sockets\&.
.IP "\fB\f(CWbacklog=<count>\fP\fP" 
Sets the backlog value passed with the \f(CWlisten()\fP system call to <count>
[int]\&. Default is 5\&. 
.br 
.PP 
\fI\fBCHILD option group\fP\fP
.PP 
Options for addresses with multiple connections via child processes\&.
.IP "\fB\f(CWfork\fP\fP" 
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 (example)\&.
.br 
SSL-CONNECT and SSL-LISTEN differ in when they actually fork off the child:
SSL-LISTEN forks \fIbefore\fP the SSL handshake, while SSL-CONNECT forks
\fIafterwards\fP\&.
RETRY and FOREVER options are not inherited by the child process\&.
.br 
.PP 
.br 
.PP 
\fI\fBEXEC option group\fP\fP
.PP 
Options for addresses that invoke a program\&.
.IP "\fB\f(CWpath=<string>\fP\fP" 
Overrides the PATH environment variable for searching the program with
<string>\&. This
\f(CW$PATH\fP value is effective in the child process too\&.
.IP "\fB\f(CWlogin\fP\fP" 
Prefixes \f(CWargv[0]\fP for the \f(CWexecvp()\fP call with \'-\', thus making a
shell behave as login shell\&.
.PP 
.br 
.PP 
\fI\fBFORK option group\fP\fP
.PP 
EXEC or SYSTEM addresses invoke a program using a child process and transfer data between \fBsocat\fP and the program\&. The interprocess communication mechanism can be influenced with the following options\&. Per
default, a \f(CWsocketpair()\fP is created and assigned to stdin and stdout of
the child process, while stderr is inherited from the \fBsocat\fP process, and the
child process uses file descriptors 0 and 1 for communicating with the main
socat process\&.
.IP "\fB\f(CWnofork\fP\fP" 
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:
.IP o 
this option can only be applied to the second \fBsocat\fP address\&.
.IP o 
it cannot be applied to a part of a dual address\&.
.IP o 
the first socat address cannot be OPENSSL or READLINE
.IP o 
socat options -b, -t, -D, -l, -v, -x become useless
.IP o 
for both addresses, options ignoreeof, cr, and crnl become useless
.IP o 
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\&.
.IP "\fB\f(CWpipes\fP\fP" 
Creates a pair of unnamed pipes for interprocess communication instead of a
socket pair\&.
.IP "\fB\f(CWopenpty\fP\fP" 
Establishes communication with the sub process using a pseudo terminal
created with \f(CWopenpty()\fP instead of the default (socketpair or ptmx)\&.
.IP "\fB\f(CWptmx\fP\fP" 
Establishes communication with the sub process using a pseudo terminal
created by opening \fB/dev/ptmx\fP or \fB/dev/ptc\fP instead of the default
(socketpair)\&.
.IP "\fB\f(CWpty\fP\fP" 
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 (example)\&.
.IP "\fB\f(CWctty\fP\fP" 
Makes the pty the controlling tty of the sub process (example)\&.
.IP "\fB\f(CWstderr\fP\fP" 
Directs stderr of the sub process to its output channel by making stderr a
\f(CWdup()\fP of stdout (example)\&. 
.IP "\fB\f(CWfdin=<fdnum>\fP\fP" 
Assigns the sub processes input channel to its file descriptor
<fdnum> 
instead of stdin (0)\&. The program started from the subprocess has to use
this fd for reading data from \fBsocat\fP (example)\&. 
.IP "\fB\f(CWfdout=<fdnum>\fP\fP" 
Assigns the sub processes output channel to its file descriptor
<fdnum> 
instead of stdout (1)\&. The program started from the subprocess has to use 
this fd for writing data to \fBsocat\fP (example)\&.
.IP "\fB\f(CWsighup\fP\fP, \fB\f(CWsigint\fP\fP, \fB\f(CWsigquit\fP\fP" 
Has \fBsocat\fP pass an eventual signal of this type to the sub process\&.
If no address has this option, socat terminates on these signals\&.
.PP 
.br 
.PP 
\fI\fBTERMIOS option group\fP\fP
.PP 
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 \fBsocat\fP\'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\&.
.PP 
.IP "\fB\f(CWb0\fP\fP" 
Disconnects the terminal\&.
.IP "\fB\f(CWb19200\fP\fP" 
Sets the serial line speed to 19200 baud\&. Some other rates are possible; use
something like \f(CWsocat -hh |grep \' b[1-9]\'\fP to find all speeds supported by
your implementation\&.
.br 
Note: On some operating systems, these options may not be
available\&. Use ispeed or ospeed
instead\&.
.IP "\fB\f(CWecho=<bool>\fP\fP" 
Enables or disables local echo (example)\&.
.IP "\fB\f(CWicanon=<bool>\fP\fP" 
Sets or clears canonical mode, enabling line buffering and some special
characters\&. 
.IP "\fB\f(CWraw\fP\fP" 
Sets raw mode, thus passing input and output almost unprocessed (example)\&.
.IP "\fB\f(CWignbrk=<bool>\fP\fP" 
Ignores or interpretes the BREAK character (e\&.g\&., ^C)
.IP "\fB\f(CWbrkint=<bool>\fP\fP" 
.IP "\fB\f(CWbs0\fP\fP" 
.IP "\fB\f(CWbs1\fP\fP" 
.IP "\fB\f(CWbsdly=<0|1>\fP\fP" 
.IP "\fB\f(CWclocal=<bool>\fP\fP" 
.IP 
\.LP
\.nf
\fBcr0
cr1
cr2
cr3\fP
\.fi
\.IP
Sets the carriage return delay to 0, 1, 2, or 3, respectively\&.
0 means no delay, the other values are terminal dependent\&.
.IP 
.IP "\fB\f(CWcrdly=<0|1|2|3>\fP\fP" 
.IP "\fB\f(CWcread=<bool>\fP\fP" 
.IP "\fB\f(CWcrtscts=<bool>\fP\fP" 
.IP 
\.LP
\.nf
\fBcs5 
cs6 
cs7 
cs8\fP
\.fi
\.IP
Sets the character size to 5, 6, 7, or 8 bits, respectively\&.
.IP 
.IP "\fB\f(CWcsize=<0|1|2|3>\fP\fP" 
.IP "\fB\f(CWcstopb=<bool>\fP\fP" 
Sets two stop bits, rather than one\&.
.IP "\fB\f(CWdsusp=<byte>\fP\fP" 
Sets the value for the VDSUSP character that suspends the current foreground
process and reactivates the shell (all except Linux)\&.
.IP "\fB\f(CWechoctl=<bool>\fP\fP" 
Echos control characters in hat notation (e\&.g\&. ^A)
.IP "\fB\f(CWechoe=<bool>\fP\fP" 
.IP "\fB\f(CWechok=<bool>\fP\fP" 
.IP "\fB\f(CWechoke=<bool>\fP\fP" 
.IP "\fB\f(CWechonl=<bool>\fP\fP" 
.IP "\fB\f(CWechoprt=<bool>\fP\fP" 
.IP "\fB\f(CWeof=<byte>\fP\fP" 
.IP "\fB\f(CWeol=<byte>\fP\fP" 
.IP "\fB\f(CWeol2=<byte>\fP\fP" 
.IP "\fB\f(CWerase=<byte>\fP\fP" 
.IP "\fB\f(CWdiscard=<byte>\fP\fP" 
.IP "\fB\f(CWff0\fP\fP" 
.IP "\fB\f(CWff1\fP\fP" 
.IP "\fB\f(CWffdly=<bool>\fP\fP" 
.IP "\fB\f(CWflusho=<bool>\fP\fP" 
.IP "\fB\f(CWhupcl=<bool>\fP\fP" 
.IP "\fB\f(CWicrnl=<bool>\fP\fP" 
.IP "\fB\f(CWiexten=<bool>\fP\fP" 
.IP "\fB\f(CWigncr=<bool>\fP\fP" 
.IP "\fB\f(CWignpar=<bool>\fP\fP" 
.IP "\fB\f(CWimaxbel=<bool>\fP\fP" 
.IP "\fB\f(CWinlcr=<bool>\fP\fP" 
.IP "\fB\f(CWinpck=<bool>\fP\fP" 
.IP "\fB\f(CWintr=<byte>\fP\fP" 
.IP "\fB\f(CWisig=<bool>\fP\fP" 
.IP "\fB\f(CWispeed=<unsigned-int>\fP\fP" 
Set the baud rate for incoming data on this line\&.
.br 
See also: ospeed, b19200
dif(\fB\f(CWistrip=<bool>\fP\fP)
.IP "\fB\f(CWiuclc=<bool>\fP\fP" 
.IP "\fB\f(CWixany=<bool>\fP\fP" 
.IP "\fB\f(CWixoff=<bool>\fP\fP" 
.IP "\fB\f(CWixon=<bool>\fP\fP" 
.IP "\fB\f(CWkill=<byte>\fP\fP" 
.IP "\fB\f(CWlnext=<byte>\fP\fP" 
.IP "\fB\f(CWmin=<byte>\fP\fP" 
.IP "\fB\f(CWnl0\fP\fP" 
Sets the newline delay to 0\&.
.IP "\fB\f(CWnl1\fP\fP" 
.IP "\fB\f(CWnldly=<bool>\fP\fP" 
.IP "\fB\f(CWnoflsh=<bool>\fP\fP" 
.IP "\fB\f(CWocrnl=<bool>\fP\fP" 
.IP "\fB\f(CWofdel=<bool>\fP\fP" 
.IP "\fB\f(CWofill=<bool>\fP\fP" 
.IP "\fB\f(CWolcuc=<bool>\fP\fP" 
.IP "\fB\f(CWonlcr=<bool>\fP\fP" 
.IP "\fB\f(CWonlret=<bool>\fP\fP" 
.IP "\fB\f(CWonocr=<bool>\fP\fP" 
.IP "\fB\f(CWopost=<bool>\fP\fP" 
Enables or disables output processing; e\&.g\&., converts NL to CR-NL\&.
.IP "\fB\f(CWospeed=<unsigned-int>\fP\fP" 
Set the baud rate for outgoing data on this line\&.
.br 
See also: ispeed, b19200
.IP "\fB\f(CWparenb=<bool>\fP\fP" 
Enable parity generation on output and parity checking for input\&.
.IP "\fB\f(CWparmrk=<bool>\fP\fP" 
.IP "\fB\f(CWparodd=<bool>\fP\fP" 
.IP "\fB\f(CWpendin=<bool>\fP\fP" 
.IP "\fB\f(CWquit=<byte>\fP\fP" 
.IP "\fB\f(CWreprint=<byte>\fP\fP" 
.IP "\fB\f(CWsane\fP\fP" 
Brings the terminal to something like a useful default state\&.
.IP "\fB\f(CWstart=<byte>\fP\fP" 
.IP "\fB\f(CWstop=<byte>\fP\fP" 
.IP "\fB\f(CWsusp=<byte>\fP\fP" 
.IP "\fB\f(CWswtc=<byte>\fP\fP" 
.IP "\fB\f(CWtab0\fP\fP" 
.IP "\fB\f(CWtab1\fP\fP" 
.IP "\fB\f(CWtab2\fP\fP" 
.IP "\fB\f(CWtab3\fP\fP" 
.IP "\fB\f(CWtabdly=<unsigned-int>\fP\fP" 
.IP "\fB\f(CWtime=<byte>\fP\fP" 
.IP "\fB\f(CWtostop=<bool>\fP\fP" 
.IP "\fB\f(CWvt0\fP\fP" 
.IP "\fB\f(CWvt1\fP\fP" 
.IP "\fB\f(CWvtdly=<bool>\fP\fP" 
.IP "\fB\f(CWwerase=<byte>\fP\fP" 
.IP "\fB\f(CWxcase=<bool>\fP\fP" 
.IP "\fB\f(CWxtabs\fP\fP" 
.PP 
.br 
.PP 
\fI\fBPTY option group\fP\fP
.PP 
These options are intended for use with the pty address
type\&.
.PP 
.IP "\fB\f(CWlink=<filename>\fP\fP" 
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
(example)\&.
Beginning with \fBsocat\fP version 1\&.4\&.3, the symbolic link is removed when
the address is closed (but see option unlink-close)\&.
.IP "\fB\f(CWwait-slave\fP\fP" 
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 \f(CWpoll()\fP
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\&. 
.IP "\fB\f(CWpty-intervall=<seconds>\fP\fP" 
When the wait-slave option is set, socat
periodically checks the HUP condition using \f(CWpoll()\fP to find if the pty\'s
slave side has been opened\&. The default polling intervall is 1s\&. Use the
pty-intervall option [timeval] to change this value\&.
.PP 
.br 
.PP 
\fI\fBOPENSSL option group\fP\fP
.PP 
These options apply to the openssl and
openssl-listen address types\&.
.PP 
.IP "\fB\f(CWcipher=<cipherlist>\fP\fP" 
Selects the list of ciphers that may be used for the connection\&.
See the man page of \f(CWciphers\fP, section \fBCIPHER LIST FORMAT\fP, for
detailed information about syntax, values, and default of <cipherlist>\&.
.br 
Several cipher strings may be given, separated by \':\'\&.
Some simple cipher strings:
.IP "3DES" 
Uses a cipher suite with triple DES\&.
.IP "MD5" 
Uses a cipher suite with MD5\&.
.IP "aNULL" 
Uses a cipher suite without authentication\&.
.IP "NULL" 
Does not use encryption\&.
.IP "HIGH" 
Uses a cipher suite with "high" encryption\&.
Note that the peer must support the selected property, or the negotiation
will fail\&.
.IP "\fB\f(CWmethod=<ssl-method>\fP\fP" 
Sets the protocol version to be used\&. Valid strings (not case sensitive)
are:  
.IP "\f(CWSSLv2\fP" 
Select SSL protocol version 2\&.
.IP "\f(CWSSLv3\fP" 
Select SSL protocol version 3\&.
.IP "\f(CWSSLv23\fP" 
Select SSL protocol version 2 or 3\&. This is the default when
this option is not provided\&.
.IP "\f(CWTLSv1\fP" 
Select TLS protocol version 1\&.
.IP "\fB\f(CWverify=<bool>\fP\fP" 
Controls check of the peer\'s certificate\&. Default is 1 (true)\&. Disabling
verify might open your socket for everyone, making the encryption useless!
.IP "\fB\f(CWcert=<filename>\fP\fP" 
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\&.
.IP "\fB\f(CWkey=<filename>\fP\fP" 
Specifies the file with the private key\&. The private key may be in this
file or in the file given with the cert option\&. The party that has
to proof that it is the owner of a certificate needs the private key\&.
.IP "\fB\f(CWdhparams=<filename>\fP\fP" 
Specifies the file with the Diffie Hellman parameters\&. These parameters may
also be in the file given with the cert
option in which case the dhparams option is not needed\&.
.IP "\fB\f(CWcafile=<filename>\fP\fP" 
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\&.
.IP "\fB\f(CWcapath=<dirname>\fP\fP" 
Specifies the directory with the trusted (root) certificates\&. The directory
must contain certificates in PEM format and their hashes (see OpenSSL
documentation) 
.IP "\fB\f(CWegd=<filename>\fP\fP" 
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\&.
.IP "\fB\f(CWpseudo\fP\fP" 
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 archieved 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\&.
.br 
NOTE:This mechanism is not sufficient for generation of secure keys!
.IP "\fB\f(CWfips\fP\fP" 
Enables FIPS mode if compiled in\&. For info about the FIPS encryption
implementation standard see http://oss-institute\&.org/fips-faq\&.html\&. 
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\&.
.PP 
.br 
.PP 
\fI\fBRETRY option group\fP\fP
.PP 
Options that control retry of some system calls, especially connection
attempts\&.
.PP 
.IP "\fB\f(CWretry=<num>\fP\fP" 
Number of retries before the connection or listen attempt is aborted\&. 
Default is 0, which means just one attempt\&. 
.IP "\fB\f(CWintervall=<timespec>\fP\fP" 
Time between consecutive attempts (seconds, 
[timespec])\&. Default is 1 second\&.
.IP "\fB\f(CWforever\fP\fP" 
Performs an unlimited number of retry attempts\&.
.PP 
.br 
.PP 
\fI\fBTUN option group\fP\fP
.PP 
Options that control Linux TUN/TAP interface device addresses\&.
.PP 
.IP "\fB\f(CWtun-device=<device-file>\fP\fP" 
Instructs socat to take another path for the TUN clone device\&. Default is
\f(CW/dev/net/tun\fP\&.
.IP "\fB\f(CWtun-name=<if-name>\fP\fP" 
Gives the resulting network interface a specific name instead of the system
generated (tun0, tun1, etc\&.)
.IP "\fB\f(CWtun-type=[tun|tap]\fP\fP" 
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\&.
.IP "\fB\f(CWiff-no-pi\fP\fP" 
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\&.
.IP "\fB\f(CWiff-up\fP\fP" 
Sets the TUN network interface status UP\&. Strongly recommended\&.
.IP "\fB\f(CWiff-broadcast\fP\fP" 
Sets the BROADCAST flag of the TUN network interface\&.
.IP "\fB\f(CWiff-debug\fP\fP" 
Sets the DEBUG flag of the TUN network interface\&.
.IP "\fB\f(CWiff-loopback\fP\fP" 
Sets the LOOPBACK flag of the TUN network interface\&.
.IP "\fB\f(CWiff-pointopoint\fP\fP" 
Sets the POINTOPOINT flag of the TUN device\&.
.IP "\fB\f(CWiff-notrailers\fP\fP" 
Sets the NOTRAILERS flag of the TUN device\&.
.IP "\fB\f(CWiff-running\fP\fP" 
Sets the RUNNING flag of the TUN device\&.
.IP "\fB\f(CWiff-noarp\fP\fP" 
Sets the NOARP flag of the TUN device\&.
.IP "\fB\f(CWiff-promisc\fP\fP" 
Sets the PROMISC flag of the TUN device\&.
.IP "\fB\f(CWiff-allmulti\fP\fP" 
Sets the ALLMULTI flag of the TUN device\&.
.IP "\fB\f(CWiff-master\fP\fP" 
Sets the MASTER flag of the TUN device\&.
.IP "\fB\f(CWiff-slave\fP\fP" 
Sets the SLAVE flag of the TUN device\&.
.IP "\fB\f(CWiff-multicast\fP\fP" 
Sets the MULTICAST flag of the TUN device\&.
.IP "\fB\f(CWiff-portsel\fP\fP" 
Sets the PORTSEL flag of the TUN device\&.
.IP "\fB\f(CWiff-automedia\fP\fP" 
Sets the AUTOMEDIA flag of the TUN device\&.
.IP "\fB\f(CWiff-dynamic\fP\fP" 
Sets the DYNAMIC flag of the TUN device\&.
.PP 
.br 
.PP 
.SH "DATA VALUES" 
.PP 
This section explains the different data types that address parameters and
address options can take\&.
.PP 
.IP "address-range" 
Is currently only implemented for IPv4 and IPv6\&. See address-option
`range\' 
.IP "bool" 
"0" or "1"; if value is omitted, "1" is taken\&.
.IP "byte" 
An unsigned int number, read with \f(CWstrtoul()\fP, lower or equal to
\f(CWUCHAR_MAX\fP\&.
.IP "command-line" 
A string specifying a program name and its arguments, separated by single
spaces\&. 
.IP "data" 
A raw data specification following \fIdalan\fP syntax\&. The only documented
form is a string starting with \'x\' followed by an even number of hex digits\&.
.IP "directory" 
A string with usual UN*X directory name semantics\&.
.IP "facility" 
The name of a syslog facility in lower case characters\&.
.IP "fdnum" 
An unsigned int type, read with \f(CWstrtoul()\fP, specifying a UN*X file
descriptor\&. 
.IP "filename" 
A string with usual UN*X filename semantics\&.
.IP "group" 
If the first character is a decimal digit, the value is read with
\f(CWstrtoul()\fP as unsigned integer specifying a group id\&. Otherwise, it
must be an existing group name\&.
.IP "int" 
A number following the rules of the \f(CWstrtol()\fP 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\&.
.IP "interface" 
A string specifying the device name of a network interface, e\&.g\&. "eth0"\&.
.IP "IP address" 
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\&.
.br 
Examples: 127\&.0\&.0\&.1, [::1], www\&.dest-unreach\&.org, dns1
.IP "IPv4 address" 
An IPv4 address in numbers-and-dots notation or a hostname that resolves to
an IPv4 address\&.
.br 
Examples: 127\&.0\&.0\&.1, www\&.dest-unreach\&.org, dns2
.IP "IPv6 address" 
An iPv6 address in hexnumbers-and-colons notation enclosed in brackets, or a
hostname that resolves to an IPv6 address\&.
.br 
Examples: [::1], [1234:5678:9abc:def0:1234:5678:9abc:def0],
ip6name\&.domain\&.org 
.IP "long" 
A number read with \f(CWstrtol()\fP\&. The value must fit into a C long\&.
.IP "long long" 
A number read with \f(CWstrtoll()\fP\&. The value must fit into a C long long\&.
.IP "off_t" 
An implementation dependend signed number, usually 32 bits, read with strtol
or strtoll\&.
.IP "off64_t" 
An implementation dependend signed number, usually 64 bits, read with strtol
or strtoll\&.
.IP "mode_t" 
An unsigned integer, read with \f(CWstrtoul()\fP, specifying mode (permission)
bits\&. 
.IP "pid_t" 
A number, read with \f(CWstrtol()\fP, specifying a process id\&.
.IP "port" 
A uint16_t (16 bit unsigned number) specifying a TCP or UDP port, read
with \f(CWstrtoul()\fP\&.
.IP "protocol" 
An unsigned 8 bit number, read with \f(CWstrtoul()\fP\&.
.IP "size_t" 
An unsigned number with size_t limitations, read with \f(CWstrtoul\fP\&.
.IP "sockname" 
A socket address\&. See address-option `bind\'
.IP "string" 
A sequence of characters, not containing \'\e0\' and, depending on
the position within the command line, \':\', \',\', or "!!"\&. Note
that you might have to escape shell meta characters in the command line\&.
.IP "TCP service" 
A service name, not starting with a digit, that is resolved by
\f(CWgetservbyname()\fP, or an unsigned int 16 bit number read with
\f(CWstrtoul()\fP\&.
.IP "timeval" 
A double float specifying seconds; the number is mapped into a
struct timeval, consisting of seconds and microseconds\&.
.IP "timespec" 
A double float specifying seconds; the number is mapped into a
struct timespec, consisting of seconds and nanoseconds\&.
.IP "UDP service" 
A service name, not starting with a digit, that is resolved by
\f(CWgetservbyname()\fP, or an unsigned int 16 bit number read with
\f(CWstrtoul()\fP\&.
.IP "unsigned int" 
A number read with \f(CWstrtoul()\fP\&. The value must fit into a C unsigned
int\&. 
.IP "user" 
If the first character is a decimal digit, the value is read with
\f(CWstrtoul()\fP as unsigned integer specifying a user id\&. Otherwise, it must
be an existing user name\&.
.PP 
.SH "EXAMPLES" 
.PP 
.IP 
.IP "\fB\f(CWsocat - TCP4:www\&.domain\&.org:80\fP\fP" 
.IP 
Transfers data between STDIO (-) and a
TCP4 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\&.
.IP 
\.LP
\.nf
\fBsocat -d -d READLINE,history=$HOME/.http_history \\ 
TCP4:www.domain.org:www,crnl\fP
\.fi
.IP 
.IP 
This is similar to the previous example, but you can edit the current line in a
bash like manner (READLINE) and use the
history file \&.http_history; \fBsocat\fP 
prints messages about progress (-d -d)\&. The  port is specified by service name
(www), and correct network line termination characters (crnl) instead of NL
are used\&.
.IP 
.IP "\fB\f(CWsocat TCP4-LISTEN:www TCP4:www\&.domain\&.org:www\fP\fP" 
.IP 
Installs a simple TCP port forwarder\&. With
TCP4-LISTEN it listens on local port "www" until a
connection comes in, accepts it, then connects to the remote host
(TCP4) and starts data transfer\&. It will not accept a
second connection\&. 
.IP 
\.LP
\.nf
\fBsocat -d -d -lmlocal2 \\ 
TCP4-LISTEN:80,bind=myaddr1,reuseaddr,fork,su=nobody,range=10.0.0.0/8 \\ 
TCP4:www.domain.org:80,bind=myaddr2\fP
\.fi
.IP 
.IP 
TCP port forwarder, each side bound to another local IP address
(bind)\&. This example handles an almost
arbitrary number of parallel or consecutive connections by
fork\'ing a new 
process after each \f(CWaccept()\fP\&. It provides a little security by
su\'ing to user 
nobody after forking; it only permits connections from the private 10 network (range);
due to reuseaddr, it allows immediate restart after master process\'s
termination, even if some child sockets are not completely shut down\&.
With -lmlocal2, socat logs to stderr until successfully
reaching the accept loop\&. Further logging is directed to syslog with facility
local2\&.
.IP 
\.LP
\.nf
\fBsocat TCP4-LISTEN:5555,fork,tcpwrap=script \\ 
EXEC:/bin/myscript,chroot=/home/sandbox,su-d=sandbox,pty,stderr\fP
\.fi
.IP 
.IP 
A simple server that accepts connections
(TCP4-LISTEN) and fork\'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 EXEC\'uting the program, the child process
chroot\'s 
to \fB/home/sandbox\fP, su\'s to user sandbox, and then starts 
the program \fB/home/sandbox/bin/myscript\fP\&. \fBSocat\fP and
myscript communicate via a pseudo tty (pty); myscript\'s
stderr is redirected to stdout,
so its error messages are transferred via \fBsocat\fP to the connected client\&. 
.IP 
\.LP
\.nf
\fBsocat EXEC:"mail.sh target@domain.com",fdin=3,fdout=4 \\ 
TCP4:mail.relay.org:25,crnl,bind=alias1.server.org,mss=512\fP
\.fi
.IP 
.IP 
\fBmail\&.sh\fP is a shell script, distributed with \fBsocat\fP, that implements a
simple 
SMTP client\&. It is programmed to "speak" SMTP on its FDs 3 (in) and 4 (out)\&.
The fdin and fdout options tell \fBsocat\fP
to use these FDs for communication with 
the program\&. Because mail\&.sh inherits stdin and stdout while \fBsocat\fP does not
use them, the script can read a
mail body from stdin\&. \fBSocat\fP makes alias1 your local source address
(bind), cares for correct network line termination
(crnl) and sends  
at most 512 data bytes per packet (mss)\&. 
.IP 
.IP "\fB\f(CWsocat - /dev/ttyS0,raw,echo=0,crnl\fP\fP" 
.IP 
Opens an interactive connection via the serial line, e\&.g\&. for talking with a
modem\&. raw and echo set ttyS0\'s terminal
parameters to practicable values, crnl 
converts to correct newline characters\&. Consider using
READLINE instead of `-\'\&.
.IP 
\.LP
\.nf
\fBsocat UNIX-LISTEN:/tmp/.X11-unix/X1,fork \\ 
SOCKS4:host.victim.org:127.0.0.1:6000,socksuser=nobody,sourceport=20\fP
\.fi
.IP 
.IP 
With UNIX-LISTEN, \fBsocat\fP opens a listening
UNIX domain socket \fB/tmp/\&.X11-unix/X1\fP\&. This path corresponds 
to local XWindow display :1 on your machine, so XWindow client connections to
DISPLAY=:1 are accepted\&. \fBSocat\fP then speaks with
the SOCKS4 server host\&.victim\&.org that might permit 
sourceport 20 based connections due to an FTP related
weakness in its static IP filters\&. \fBSocat\fP
pretends to be invoked by socksuser 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\&.
.IP 
.IP "\fB\f(CWsocat -u /tmp/readdata,seek-end=0,ignoreeof -\fP\fP" 
.IP 
This is an example for unidirectional data transfer
(-u)\&. \fBSocat\fP transfers data 
from file /tmp/readdata (implicit address GOPEN), starting
at its current end (seek-end=0 lets \fBsocat\fP start 
reading at current end of file; use seek=0 or no
seek option to first read the existing data) in a "tail -f" like mode
(ignoreeof)\&. The "file" 
might also be a listening UNIX domain socket (do not use a seek option then)\&. 
.IP 
\.LP
\.nf
\fB(sleep 5; echo PASSWORD; sleep 5; echo ls; sleep 1) | 
socat - EXEC:'ssh -l user server',pty,setsid,ctty\fP
\.fi
.IP 
.IP 
EXEC\'utes an ssh session to server\&. Uses a pty for communication between \fBsocat\fP and
ssh, makes it ssh\'s controlling tty (ctty), 
and makes this pty the owner of
a new process group (setsid), so ssh accepts the password from \fBsocat\fP\&.
.IP 
\.LP
\.nf
\fBsocat -u TCP4-LISTEN:3334,reuseaddr,fork \\ 
OPEN:/tmp/in.log,creat,append\fP
\.fi
.IP 
.IP 
Implements a simple network based message collector\&. 
For each client connecting to port 3334, a new child process is generated (option fork)\&.
All data sent by the clients are append\'ed to the file /tmp/in\&.log\&.
If the file does not exist, socat creat\'s it\&. 
Option reuseaddr allows immediate restart of the server
process\&. 
.IP 
.IP 
.IP "\fB\f(CWsocat READLINE,noecho=\'[Pp]assword:\' EXEC:\'ftp ftp\&.server\&.com\',pty,setsid,ctty\fP\fP" 
.IP 
Wraps a command line history (READLINE) around the EXEC\'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!
pty is required to have ftp issue a prompt\&.
Nevertheless, there may occur some confusion with the password and FTP
prompts\&.
.IP 
(\fB\f(CWsocat PTY,link=$HOME/dev/vmodem0,raw,echo=0,waitslave EXEC:\'"ssh modemserver\&.us\&.org socat - /dev/ttyS0,nonblock,raw,echo=0"\'\fP\fP)
.IP 
Generates a pseudo terminal 
device (PTY) on the client that can be reached under the
symbolic link \fB$HOME/dev/vmodem0\fP\&. 
An application that expects a serial line or modem
can be configured to use \fB$HOME/dev/vmodem0\fP; its traffic will be directed
to a modemserver via ssh where another socat instance links it with
\fB/dev/ttyS0\fP\&.
.IP 
\.LP
\.nf
\fBsocat TCP4-LISTEN:2022,reuseaddr,fork \\ 
PROXY:proxy:www.domain.org:22,proxyport=3128,proxyauth=user:pass\fP
\.fi
.IP 
.IP 
starts a forwarder that accepts connections on port 2022, and directs them 
through the proxy daemon listening on port 3128
(proxyport) on host proxy, using the
CONNECT method, where they are authenticated as "user" with "pass" (proxyauth)\&. The proxy 
should establish connections to host www\&.domain\&.org on port 22 then\&.
.IP 
.IP "\fB\f(CWsocat - SSL:server:4443,cafile=server\&.crt,cert=client\&.pem\fP\fP" 
.IP 
is an OpenSSL client that tries to establish a secure connection to an SSL
server\&. Option cafile 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 cert 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\&.
.br 
The first address (\'-\') can be replaced by almost any other socat address\&.
.IP 
.IP "\fB\f(CWsocat SSL-LISTEN:4443,reuseaddr,pf=ip4,fork,cert=server\&.pem,cafile=client\&.crt PIPE\fP\fP" 
.IP 
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\&.
.br 
The second address (\'PIPE\') can be replaced by almost any other socat
address\&.
.br 
For instructions on generating and distributing OpenSSL keys and certificates
see the additional socat docu \f(CWsocat-openssl\&.txt\fP\&.
.IP 
.IP "\fB\f(CWecho |socat -u - file:/tmp/bigfile,create,largefile,seek=100000000000\fP\fP" 
.IP 
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)\&. 
.IP 
.IP "\fB\f(CWsocat tcp-l:7777,reuseaddr,fork system:\'filan -i 0 -s >&2\',nofork\fP\fP" 
.IP 
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 (nofork)\&.  The shell starts filan and lets it print the socket addresses to
stderr (your terminal window)\&.
.IP 
.IP "\fB\f(CWecho -e "\e0\e14\e0\e0\ec" |socat -u - file:/usr/bin/squid\&.exe,seek=0x00074420\fP\fP" 
.IP 
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)\&.
.IP 
.IP "\fB\f(CWsocat - tcp:www\&.blackhat\&.org:31337,readbytes=1000\fP\fP" 
.IP 
connects to an unknown service and prevents being flooded\&.
.IP 
.IP "\fB\f(CWsocat -U TCP:target:9999,end-close TCP-L:8888,reuseaddr,fork\fP\fP" 
.IP 
merges data arriving from different TCP streams on port 8888 to just one stream
to target:9999\&. The end-close 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)\&.
.IP 
.IP "\fB\f(CWsocat - UDP4-DATAGRAM:192\&.168\&.1\&.0:123,sp=123,broadcast,range=192\&.168\&.1\&.0/24\fP\fP" 
.IP 
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\&.
.IP 
.IP "\fB\f(CWsocat - IP4-DATAGRAM:255\&.255\&.255\&.255:44,broadcast,range=10\&.0\&.0\&.0/8\fP\fP" 
.IP 
sends a broadcast to the local network(s) using protocol 44\&. Accepts replies
from the private address range only\&.
.IP 
.IP "\fB\f(CWsocat - UDP4-DATAGRAM:224\&.255\&.0\&.1:6666,bind=:6666,ip-add-membership=224\&.255\&.0\&.1:eth0\fP\fP" 
.IP 
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\&.
.IP 
.IP "\fB\f(CWsocat TCP:host2:4443 TUN:192\&.168\&.255\&.1/24,up\fP\fP" 
.IP 
establishes one side of a virtual (but not private!) network with host2 where a
similar process might run, with TCP-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\&. Substitute the TCP link with an SSL connection protected by
client and server authentication (see OpenSSL
client and 
server)\&.
.IP 
.PP 
.SH "DIAGNOSTICS" 
.PP 
\fBSocat\fP uses a logging mechanism that allows to filter 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)
.PP 
.IP "FATAL:" 
Conditions that require unconditional and immediate program termination\&.
.IP "ERROR:" 
Conditions that prevent proper program processing\&. Usually the
program is terminated (see option -s)\&.
.IP "WARNING:" 
Something did not function correctly or is in a state where
correct further processing cannot be guaranteed, but might be possible\&.
.IP "NOTICE:" 
Interesting actions of the program, e\&.g\&. for supervising \fBsocat\fP in some kind of server mode\&.
.IP "INFO:" 
Description of what the program does, and maybe why it
happens\&. Allows to monitor the lifecycles of file descriptors\&.
.IP "DEBUG:" 
Description of how the program works, all system or library calls and their results\&.
.PP 
Log messages can be written to stderr, to a file, or to syslog\&.
.PP 
On exit, \fBsocat\fP 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\&. 
.PP 
.SH "FILES" 
.PP 
/usr/bin/socat 
.br 
/usr/bin/filan 
.br 
/usr/bin/procan
.PP 
.SH "ENVIRONMENT VARIABLES" 
.PP 
.IP "\fBSOCAT_DEFAULT_LISTEN_IP\fP" 
(Values 4 or 6) Sets the IP version to be used
for listen, recv, and recvfrom addresses if no pf
(protocol-family) option is given\&. Is overridden by socat options
-4 or -6\&.
.IP 
.IP "\fBSOCAT_PREFERRED_RESOLVE_IP\fP" 
(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 pf (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\&. 
.IP 
.IP "\fBSOCAT_FORK_WAIT\fP" 
Specifies the time (seconds) to sleep the parent and
child processes after successful fork()\&. Useful for debugging\&.
.IP 
.IP "\fBHOSTNAME\fP" 
Is used to determine the hostname for logging (see
-lh)\&.
.IP 
.IP "\fBLOGNAME\fP" 
Is used as name for the socks client user name if no
socksuser is given\&.
.br 
With options su and
su-d, LOGNAME is set to the given user name\&.
.IP 
.IP "\fBUSER\fP" 
Is used as name for the socks client user name if no
socksuser is given and LOGNAME is empty\&.
.br 
With options su and
su-d, USER is set to the given user name\&.
.IP 
.IP "\fBSHELL\fP" 
With options su and
su-d, SHELL is set to the login shell of the
given user\&.
.IP 
.IP "\fBPATH\fP" 
Can be set with option path for exec and
system addresses\&.
.IP 
.IP "\fBHOME\fP" 
With options su and
su-d, HOME is set to the home directory of the
given user\&.
.IP 
.PP 
.SH "CREDITS" 
.PP 
The work of the following groups and organizations was invaluable for this
project:
.PP 
The \fIFSF\fP (GNU, http://www\&.fsf\&.org/ project 
with their free and portable development software and
lots of other useful tools and libraries\&.
.PP 
The \fILinux developers community\fP (http://www\&.linux\&.org/) for providing a free, open source operating
system\&.
.PP 
The \fIOpen Group\fP (http://www\&.unix-systems\&.org/) for making their
standard specifications available on the Internet for free\&.
.PP 
.SH "VERSION" 
.PP 
This man page describes version 1\&.6\&.0 of \fBsocat\fP\&.
.PP 
.SH "BUGS" 
.PP 
Addresses cannot be nested, so a single socat process cannot, e\&.g\&., drive ssl
over socks\&.
.PP 
Address option ftruncate without value uses default 1 instead of 0\&.
.PP 
Verbose modes (-x and/or -v) display line termination characters inconsistently
when address options cr or crnl are used: They show the data \fIafter\fP
conversion in either direction\&.
.PP 
The data transfer blocksize setting (-b) is ignored with address readline\&.
.PP 
Send bug reports to <socat@dest-unreach\&.org>
.PP 
.SH "SEE ALSO" 
.PP 
nc(1), netcat6(1), sock(1), rinetd(8), cage(1), socks\&.conf(5), openssl(1),
stunnel(8), pty(1), rlwrap(1), setsid(1)
.PP 
\fBSocat\fP home page http://www\&.dest-unreach\&.org/socat/
.PP 
.SH "AUTHOR" 
.PP 
Gerhard Rieger <rieger@dest-unreach\&.org>