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CentOS 7.0 - man page for socat (centos section 1)

socat(1)										 socat(1)

NAME
       socat - Multipurpose relay (SOcket CAT)

SYNOPSIS
       socat [options] <address> <address>
       socat -V
       socat -h[h[h]] | -?[?[?]]
       filan
       procan

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

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

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

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

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

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

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

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

OPTIONS
       Socat 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 speci-
       fications.

       -V     Print version and available feature information to stdout, and exit.

       -h | -?
	      Print a help text to stdout describing command line options and  available  address
	      types, and exit.

       -hh | -??
	      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 particu-
	      lar implementation.

       -hhh | -???
	      Like -hh, plus a list of all available address option names.

       -d     Without  this  option,  only  fatal and error messages are generated; applying this
	      option also prints warning messages. See DIAGNOSTICS for more information.

       -d -d  Prints fatal, error, warning, and notice messages.

       -d -d -d
	      Prints fatal, error, warning, notice, and info messages.

       -d -d -d -d
	      Prints fatal, error, warning, notice, info, and debug messages.

       -D     Logs information about file descriptors before starting the transfer phase.

       -ly[<facility>]
	      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".

       -lf <logfile>
	      Writes messages to <logfile> [filename] instead of stderr.

       -ls    Writes messages to stderr (this is the default).

       -lp<progname>
	      Overrides  the  program  name  printed  in error messages and used for constructing
	      environment variable names.

       -lu    Extends the timestamp of error messages to microsecond resolution.  Does	not  work
	      when logging to syslog.

       -lm[<facility>]
	      Mixed  log  mode.  During startup messages are printed to stderr; when socat starts
	      the transfer phase loop or daemon mode (i.e. after opening all streams  and  before
	      starting	data  transfer,  or,  with listening sockets with fork option, before the
	      first accept call), it switches logging to syslog.  With optional  <facility>,  the
	      syslog type can be selected, default is "daemon".

       -lh    Adds hostname to log messages. Uses the value from environment variable HOSTNAME or
	      the value retrieved with uname() if HOSTNAME is not set.

       -v     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.

       -x     Writes the transferred data not only to their target streams, but also  to  stderr.
	      The output format is hexadecimal, prefixed with "> " or "< " indicating flow direc-
	      tions. Can be combined with -v .

       -b<size>
	      Sets the data transfer block <size> [size_t].  At most <size> bytes are transferred
	      per step. Default is 8192 bytes.

       -s     By  default,  socat  terminates  when an error occurred to prevent the process from
	      running when some option could not be applied. With this option,	socat  is  sloppy
	      with  errors  and  tries	to  continue.  Even  with this option, socat will exit on
	      fatals, and will abort connection attempts when security checks failed.

       -t<timeout>
	      When one channel has reached EOF, the write part of the other channel is shut down.
	      Then,  socat  waits  <timeout> [timeval] seconds before terminating. Default is 0.5
	      seconds. This timeout only applies to addresses where write and read  part  can  be
	      closed  independently.  When  during  the timeout interval the read part gives EOF,
	      socat terminates without awaiting the timeout.

       -T<timeout>
	      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 trans-
	      fer EOF.

       -u     Uses  unidirectional mode. The first address is only used for reading, and the sec-
	      ond address is only used for writing (example).

       -U     Uses unidirectional mode in reverse direction. The first address is only	used  for
	      writing, and the second address is only used for reading.

       -g     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.

       -L<lockfile>
	      If  lockfile  exists,  exits with error. If lockfile does not exist, creates it and
	      continues, unlinks lockfile on exit.

       -W<lockfile>
	      If lockfile exists, waits until it disappears. When lockfile does not  exist,  cre-
	      ates it and continues, unlinks lockfile on exit.

       -4     Use IP version 4 in case that the addresses do not implicitly or explicitly specify
	      a version; this is the default.

       -6     Use IP version 6 in case that the addresses do not implicitly or explicitly specify
	      a version.

ADDRESS SPECIFICATIONS
       With  the address command line arguments, the user gives socat instructions and the neces-
       sary information for establishing the byte streams.

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

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

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

       Zero or more address options may be given with each address. They influence the address in
       some  ways.   Options consist of an option keyword or an option keyword and a value, sepa-
       rated 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).

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

       Usually,  addresses  are  opened  in  read/write  mode.	When an address is part of a dual
       address specification, or when 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.

       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 charac-
       ters ( { [ ' is found, the corresponding closing character - ) } ] ' - is looked for; they
       may also be nested. Within these constructs, socats special characters and strings : ,  !!
       are  not  handled  specially.  All  those  characters and strings can be escaped with \ or
       within ""

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

       CREATE:<filename>
	      Opens  <filename>  with  creat()	and  uses  the file descriptor for writing.  This
	      address type requires write-only context, because a file opened with  creat  cannot
	      be read from.
	      Flags  like  O_LARGEFILE	cannot be applied. If you need them use OPEN with options
	      create,create.
	      <filename> must be a valid existing or not existing path.  If <filename> is a named
	      pipe, creat() might block; if <filename> refers to a socket, this is an error.
	      Option groups: FD,REG,NAMED
	      Useful options: mode, user, group, unlink-early, unlink-late, append
	      See also: OPEN, GOPEN

       EXEC:<command-line>
	      Forks  a	sub  process  that  establishes communication with its parent process and
	      invokes the specified program with execvp() .  <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  execvp()  semantics for finding the program via $PATH apply. After suc-
	      cessful program start, socat writes data to stdin of the process and reads from its
	      stdout using a UNIX domain socket generated by socketpair() per default. (example)
	      Option groups: FD,SOCKET,EXEC,FORK,TERMIOS
	      Useful  options:	path,  fdin,  fdout, chroot, su, su-d, nofork, pty, stderr, ctty,
	      setsid, pipes, login, sigint, sigquit
	      See also: SYSTEM

       FD:<fdnum>
	      Uses the file descriptor <fdnum>. It must already exist as valid UN*X file descrip-
	      tor.
	      Option groups: FD (TERMIOS,REG,SOCKET)
	      See also: STDIO, STDIN, STDOUT, STDERR

       GOPEN:<filename>
	      (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, socat connects; if
	      connecting fails, socat assumes a datagram socket and uses sendto() calls.  If  the
	      entry  is  not a socket, socat opens it applying the O_APPEND flag.  If it does not
	      exist, it is opened with flag O_CREAT as a regular file (example).
	      Option groups: FD,REG,SOCKET,NAMED,OPEN
	      See also: OPEN, CREATE, UNIX-CONNECT

       IP-SENDTO:<host>:<protocol>
	      Opens a raw IP socket. Depending on host specification or option	pf,  IP  protocol
	      version  4  or 6 is used. It uses <protocol> to send packets to <host> [IP address]
	      and receives packets from host, ignores packets from  other  hosts.   Protocol  255
	      uses the raw socket with the IP header being part of the data.
	      Option groups: FD,SOCKET,IP4,IP6
	      Useful options: pf, ttl
	      See also: IP4-SENDTO, IP6-SENDTO, IP-RECVFROM, IP-RECV, UDP-SENDTO, UNIX-SENDTO

       INTERFACE:<interface>
	      Communicates  with  a network connected on an interface using raw packets including
	      link level data. <interface> is the name of the network interface.  Currently  only
	      available on Linux.  Option groups: FD,SOCKET
	      Useful options: pf, type
	      See also: ip-recv

       IP4-SENDTO:<host>:<protocol>
	      Like IP-SENDTO, but always uses IPv4.
	      Option groups: FD,SOCKET,IP4

       IP6-SENDTO:<host>:<protocol>
	      Like IP-SENDTO, but always uses IPv6.
	      Option groups: FD,SOCKET,IP6

       IP-DATAGRAM:<address>:<protocol>
	      Sends outgoing data to the specified address which may in particular be a broadcast
	      or multicast address. Packets arriving on the local socket  are  checked	if  their
	      source  addresses match RANGE or TCPWRAP options. This address type can for example
	      be used for implementing symmetric or asymmetric broadcast or multicast  communica-
	      tions.
	      Option groups: FD, SOCKET, IP4, IP6, RANGE
	      Useful  options:	bind,  range,  tcpwrap,  broadcast,  ip-multicast-loop, ip-multi-
	      cast-ttl, ip-multicast-if, ip-add-membership, ttl, tos, pf
	      See also: IP4-DATAGRAM, IP6-DATAGRAM, IP-SENDTO, IP-RECVFROM, IP-RECV, UDP-DATAGRAM

       IP4-DATAGRAM:<host>:<protocol>
	      Like IP-DATAGRAM, but always uses IPv4.  (example)
	      Option groups: FD,SOCKET,IP4,RANGE

       IP6-DATAGRAM:<host>:<protocol>
	      Like IP-DATAGRAM, but always uses IPv6. Please note that IPv6 does not know  broad-
	      casts.
	      Option groups: FD,SOCKET,IP6,RANGE

       IP-RECVFROM:<protocol>
	      Opens  a raw IP socket of <protocol>. Depending on option pf, IP protocol version 4
	      or 6 is used. It receives one packet from an unspecified peer and may send  one  or
	      more  answer  packets  to  that  peer.   This mode is particularly useful with fork
	      option where each arriving packet - from arbitrary peers - is handled  by  its  own
	      sub  process.   This  allows  a behaviour similar to typical UDP based servers like
	      ntpd or named.
	      Please note that the reply packets might be fetched as incoming traffic when sender
	      and  receiver  IP  address are identical because there is no port number to distin-
	      guish the sockets.
	      This address works well with IP-SENDTO address peers  (see  above).   Protocol  255
	      uses the raw socket with the IP header being part of the data.
	      Option groups: FD,SOCKET,IP4,IP6,CHILD,RANGE
	      Useful options: pf, fork, range, ttl, broadcast
	      See   also:   IP4-RECVFROM,   IP6-RECVFROM,   IP-SENDTO,	 IP-RECV,   UDP-RECVFROM,
	      UNIX-RECVFROM

       IP4-RECVFROM:<protocol>
	      Like IP-RECVFROM, but always uses IPv4.
	      Option groups: FD,SOCKET,IP4,CHILD,RANGE

       IP6-RECVFROM:<protocol>
	      Like IP-RECVFROM, but always uses IPv6.
	      Option groups: FD,SOCKET,IP6,CHILD,RANGE

       IP-RECV:<protocol>
	      Opens a raw IP socket of <protocol>. Depending on option pf, IP protocol version	4
	      or  6  is  used. It receives packets from multiple unspecified peers and merges the
	      data.  No replies are possible.  It can be,  e.g.,  addressed  by  socat	IP-SENDTO
	      address  peers.	Protocol 255 uses the raw socket with the IP header being part of
	      the data.
	      Option groups: FD,SOCKET,IP4,IP6,RANGE
	      Useful options: pf, range
	      See also: IP4-RECV, IP6-RECV, IP-SENDTO, IP-RECVFROM, UDP-RECV, UNIX-RECV

       IP4-RECV:<protocol>
	      Like IP-RECV, but always uses IPv4.
	      Option groups: FD,SOCKET,IP4,RANGE

       IP6-RECV:<protocol>
	      Like IP-RECV, but always uses IPv6.
	      Option groups: FD,SOCKET,IP6,RANGE

       OPEN:<filename>
	      Opens <filename> using the open() system call (example).	This operation	fails  on
	      UNIX domain sockets.
	      Note: This address type is rarly useful in bidirectional mode.
	      Option groups: FD,REG,NAMED,OPEN
	      Useful options: creat, excl, noatime, nofollow, append, rdonly, wronly, lock, read-
	      bytes, ignoreeof
	      See also: CREATE, GOPEN, UNIX-CONNECT

       OPENSSL:<host>:<port>
	      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.
	      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!
	      Option groups: FD,SOCKET,IP4,IP6,TCP,OPENSSL,RETRY
	      Useful options: cipher, method, verify, cafile, capath, certificate, key, compress,
	      bind, pf, connect-timeout, sourceport, retry
	      See also: OPENSSL-LISTEN, TCP

       OPENSSL-LISTEN:<port>
	      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.
	      Note: You probably want to use the certificate option with this address.
	      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!
	      Option groups: FD,SOCKET,IP4,IP6,TCP,LISTEN,OPENSSL,CHILD,RANGE,RETRY
	      Useful options: pf, cipher, method, verify, cafile, capath, certificate, key,  com-
	      press, fork, bind, range, tcpwrap, su, reuseaddr, retry
	      See also: OPENSSL, TCP-LISTEN

       PIPE:<filename>
	      If  <filename> already exists, it is opened.  If it does not exist, a named pipe is
	      created and opened. Beginning with socat version 1.4.3, the named pipe  is  removed
	      when the address is closed (but see option unlink-close
	      Note: When a pipe is used for both reading and writing, it works as echo service.
	      Note:  When  a  pipe is used for both reading and writing, and socat tries to write
	      more bytes than the pipe can buffer (Linux 2.4: 2048  bytes),  socat  might  block.
	      Consider using socat option, e.g., -b 2048
	      Option groups: FD,NAMED,OPEN
	      Useful options: rdonly, nonblock, group, user, mode, unlink-early
	      See also: unnamed pipe

       PIPE   Creates  an  unnamed pipe and uses it for reading and writing. It works as an echo,
	      because everything written to it appeares immediately as read data.
	      Note: When socat tries to write more bytes than the pipe can queue (Linux 2.4: 2048
	      bytes), socat might block. Consider, e.g., using option -b 2048
	      Option groups: FD
	      See also: named pipe

       PROXY:<proxy>:<hostname>:<port>
	      Connects	to an HTTP proxy server on port 8080 using TCP/IP  version 4 or 6 depend-
	      ing 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.
	      Option groups: FD,SOCKET,IP4,IP6,TCP,HTTP,RETRY
	      Useful  options: proxyport, ignorecr, proxyauth, resolve, crnl, bind, connect-time-
	      out, mss, sourceport, retry
	      See also: SOCKS, TCP

       PTY    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).
	      Option groups: FD,NAMED,PTY,TERMIOS
	      Useful options: link, openpty, wait-slave, mode, user, group
	      See also: UNIX-LISTEN, PIPE, EXEC, SYSTEM

       READLINE
	      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.
	      Option groups: FD,READLINE,TERMIOS
	      Useful options: history, noecho
	      See also: STDIO

       SCTP-CONNECT:<host>:<port>
	      Establishes an SCTP stream connection to the  specified  <host>  [IP  address]  and
	      <port>  [TCP  service]  using TCP/IP version 4 or 6 depending on address specifica-
	      tion, name resolution, or option pf.
	      Option groups: FD,SOCKET,IP4,IP6,SCTP,CHILD,RETRY
	      Useful  options:	bind,  pf,  connect-timeout,   tos,   mtudiscover,   sctp-maxseg,
	      sctp-nodelay, nonblock, sourceport, retry, readbytes
	      See also: SCTP4-CONNECT, SCTP6-CONNECT, SCTP-LISTEN, TCP-CONNECT

       SCTP4-CONNECT:<host>:<port>
	      Like SCTP-CONNECT, but only supports IPv4 protocol.
	      Option groups: FD,SOCKET,IP4,SCTP,CHILD,RETRY

       SCTP6-CONNECT:<host>:<port>
	      Like SCTP-CONNECT, but only supports IPv6 protocol.
	      Option groups: FD,SOCKET,IP6,SCTP,CHILD,RETRY

       SCTP-LISTEN:<port>
	      Listens  on <port> [TCP service] and accepts a TCP/IP connection. The IP version is
	      4 or the one specified with address option pf, socat option (-4, -6),  or  environ-
	      ment  variable  SOCAT_DEFAULT_LISTEN_IP.	 Note  that  opening this address usually
	      blocks until a client connects.
	      Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,IP6,SCTP,RETRY
	      Useful options: crnl,  fork,  bind,  range,  tcpwrap,  pf,  max-children,  backlog,
	      sctp-maxseg, sctp-nodelay, su, reuseaddr, retry, cool-write
	      See also: SCTP4-LISTEN, SCTP6-LISTEN, TCP-LISTEN, SCTP-CONNECT

       SCTP4-LISTEN:<port>
	      Like SCTP-LISTEN, but only supports IPv4 protocol.
	      Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,SCTP,RETRY

       SCTP6-LISTEN:<port>
	      Like SCTP-LISTEN, but only supports IPv6 protocol.
	      Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP6,SCTP,RETRY

       SOCKET-CONNECT:<domain>:<protocol>:<remote-address>
	      Creates  a  stream  socket  using  the first and second given socket parameters and
	      SOCK_STREAM (see man socket\(2)) and  connects  to  the  remote-address.	 The  two
	      socket  parameters  have to be specified by int numbers. Consult your OS documenta-
	      tion and include files to find the appropriate values. The remote-address  must  be
	      the  data representation of a sockaddr structure without sa_family and (BSD) sa_len
	      components.
	      Please note that you can - beyond the options of the specified groups  -	also  use
	      options of higher level protocols when you apply socat option -g.
	      Option groups: FD,SOCKET,CHILD,RETRY
	      Useful options: bind, setsockopt-int, setsockopt-bin, setsockopt-string
	      See also: TCP, UDP-CONNECT, UNIX-CONNECT, SOCKET-LISTEN, SOCKET-SENDTO

       SOCKET-DATAGRAM:<domain>:<type>:<protocol>:<remote-address>
	      Creates  a  datagram  socket using the first three given socket parameters (see man
	      socket\(2)) and sends outgoing data to the remote-address. The three socket parame-
	      ters have to be specified by int numbers. Consult your OS documentation and include
	      files to find the appropriate values. The remote-address must be the data represen-
	      tation of a sockaddr structure without sa_family and (BSD) sa_len components.
	      Please  note  that  you can - beyond the options of the specified groups - also use
	      options of higher level protocols when you apply socat option -g.
	      Option groups: FD,SOCKET,RANGE
	      Useful options: bind, range, setsockopt-int, setsockopt-bin, setsockopt-string
	      See also: UDP-DATAGRAM, IP-DATAGRAM, SOCKET-SENDTO, SOCKET-RECV, SOCKET-RECVFROM

       SOCKET-LISTEN:<domain>:<protocol>:<local-address>
	      Creates a stream socket using the first and  second  given  socket  parameters  and
	      SOCK_STREAM   (see   man	 socket\(2))   and  waits  for	incoming  connections  on
	      local-address. The two socket parameters have to be specified by int numbers.  Con-
	      sult  your  OS  documentation and include files to find the appropriate values. The
	      local-address must be the data  representation  of  a  sockaddr  structure  without
	      sa_family and (BSD) sa_len components.
	      Please  note  that  you can - beyond the options of the specified groups - also use
	      options of higher level protocols when you apply socat option -g.
	      Option groups: FD,SOCKET,LISTEN,RANGE,CHILD,RETRY
	      Useful options: setsockopt-int, setsockopt-bin, setsockopt-string
	      See   also:   TCP,   UDP-CONNECT,   UNIX-CONNECT,   SOCKET-LISTEN,   SOCKET-SENDTO,
	      SOCKET-SENDTO

       SOCKET-RECV:<domain>:<type>:<protocol>:<local-address>
	      Creates  a  socket using the three given socket parameters (see man socket\(2)) and
	      binds it to <local-address>. Receives arriving data. The three parameters  have  to
	      be  specified  by  int  numbers. Consult your OS documentation and include files to
	      find the appropriate values. The local-address must be the data representation of a
	      sockaddr structure without sa_family and (BSD) sa_len components.
	      Option groups: FD,SOCKET,RANGE
	      Useful options: range, setsockopt-int, setsockopt-bin, setsockopt-string
	      See   also:   UDP-RECV,	IP-RECV,   UNIX-RECV,	SOCKET-DATAGRAM,   SOCKET-SENDTO,
	      SOCKET-RECVFROM

       SOCKET-RECVFROM:<domain>:<type>:<protocol>:<local-address>
	      Creates a socket using the three given socket parameters (see man  socket\(2))  and
	      binds  it  to <local-address>. Receives arriving data and sends replies back to the
	      sender. The first three parameters have to be specified  as  int	numbers.  Consult
	      your  OS	documentation  and  include  files  to	find  the appropriate values. The
	      local-address must be the data  representation  of  a  sockaddr  structure  without
	      sa_family and (BSD) sa_len components.
	      Option groups: FD,SOCKET,CHILD,RANGE
	      Useful options: fork, range, setsockopt-int, setsockopt-bin, setsockopt-string
	      See also: UDP-RECVFROM, IP-RECVFROM, UNIX-RECVFROM, SOCKET-DATAGRAM, SOCKET-SENDTO,
	      SOCKET-RECV

       SOCKET-SENDTO:<domain>:<type>:<protocol>:<remote-address>
	      Creates a socket using the three given  socket  parameters  (see	man  socket\(2)).
	      Sends  outgoing  data to the given address and receives replies.	The three parame-
	      ters have to be specified as int numbers. Consult your OS documentation and include
	      files to find the appropriate values. The remote-address must be the data represen-
	      tation of a sockaddr structure without sa_family and (BSD) sa_len components.
	      Option groups: FD,SOCKET
	      Useful options: bind, setsockopt-int, setsockopt-bin, setsockopt-string
	      See  also:  UDP-SENDTO,  IP-SENDTO,   UNIX-SENDTO,   SOCKET-DATAGRAM,   SOCKET-RECV
	      SOCKET-RECVFROM

       SOCKS4:<socks-server>:<host>:<port>
	      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).
	      Option groups: FD,SOCKET,IP4,IP6,TCP,SOCKS4,RETRY
	      Useful options: socksuser, socksport, sourceport, pf, retry
	      See also: SOCKS4A, PROXY, TCP

       SOCKS4A:<socks-server>:<host>:<port>
	      like  SOCKS4, but uses socks protocol version 4a, thus leaving host name resolution
	      to the socks server.
	      Option groups: FD,SOCKET,IP4,IP6,TCP,SOCKS4,RETRY

       STDERR Uses file descriptor 2.
	      Option groups: FD (TERMIOS,REG,SOCKET)
	      See also: FD

       STDIN  Uses file descriptor 0.
	      Option groups: FD (TERMIOS,REG,SOCKET)
	      Useful options: readbytes
	      See also: FD

       STDIO  Uses file descriptor 0 for reading, and 1 for writing.
	      Option groups: FD (TERMIOS,REG,SOCKET)
	      Useful options: readbytes
	      See also: FD

       STDOUT Uses file descriptor 1.
	      Option groups: FD (TERMIOS,REG,SOCKET)
	      See also: FD

       SYSTEM:<shell-command>
	      Forks a sub process that establishes communication  with	its  parent  process  and
	      invokes  the  specified  program	with  system() . Please note that <shell-command>
	      [string] must not contain ',' or "!!", and that shell meta characters may  have  to
	      be  protected.   After  successful program start, socat writes data to stdin of the
	      process and reads from its stdout.
	      Option groups: FD,SOCKET,EXEC,FORK,TERMIOS
	      Useful options: path, fdin, fdout, chroot, su, su-d,  nofork,  pty,  stderr,  ctty,
	      setsid, pipes, sigint, sigquit
	      See also: EXEC

       TCP:<host>:<port>
	      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.
	      Option groups: FD,SOCKET,IP4,IP6,TCP,RETRY
	      Useful options: crnl, bind, pf, connect-timeout, tos,  mtudiscover,  mss,  nodelay,
	      nonblock, sourceport, retry, readbytes
	      See also: TCP4, TCP6, TCP-LISTEN, UDP, SCTP-CONNECT, UNIX-CONNECT

       TCP4:<host>:<port>
	      Like TCP, but only supports IPv4 protocol (example).
	      Option groups: FD,SOCKET,IP4,TCP,RETRY

       TCP6:<host>:<port>
	      Like TCP, but only supports IPv6 protocol.
	      Option groups: FD,SOCKET,IP6,TCP,RETRY

       TCP-LISTEN:<port>
	      Listens  on <port> [TCP service] and accepts a TCP/IP connection. The IP version is
	      4 or the one specified with address option pf, socat option (-4, -6),  or  environ-
	      ment  variable  SOCAT_DEFAULT_LISTEN_IP.	 Note  that  opening this address usually
	      blocks until a client connects.
	      Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,IP6,TCP,RETRY
	      Useful options: crnl, fork, bind, range, tcpwrap, pf, max-children,  backlog,  mss,
	      su, reuseaddr, retry, cool-write
	      See   also:   TCP4-LISTEN,   TCP6-LISTEN,   UDP-LISTEN,  SCTP-LISTEN,  UNIX-LISTEN,
	      OPENSSL-LISTEN, TCP-CONNECT

       TCP4-LISTEN:<port>
	      Like TCP-LISTEN, but only supports IPv4 protocol (example).
	      Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,TCP,RETRY

       TCP6-LISTEN:<port>
	      Like TCP-LISTEN, but only supports IPv6 protocol.
	      Additional useful option: ipv6only
	      Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP6,TCP,RETRY

       TUN[:<if-addr>/<bits>]
	      Creates a Linux TUN/TAP device and optionally assignes it the address  and  netmask
	      given by the parameters. The resulting network interface is almost ready for use by
	      other processes; socat serves its "wire side". This address requires read and write
	      access  to  the tunnel cloning device, usually /dev/net/tun , as well as permission
	      to set some ioctl()s.  Option iff-up is required to immediately activate the inter-
	      face!
	      Option groups: FD,NAMED,OPEN,TUN
	      Useful options: iff-up, tun-device, tun-name, tun-type, iff-no-pi
	      See also: ip-recv

       UDP:<host>:<port>
	      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.
	      Please note that, due to UDP protocol properties,  no  real  connection  is  estab-
	      lished; data has to be sent for `connecting' to the server, and no end-of-file con-
	      dition can be transported.
	      Option groups: FD,SOCKET,IP4,IP6
	      Useful options: ttl, tos, bind, sourceport, pf
	      See also: UDP4, UDP6, UDP-LISTEN, TCP, IP

       UDP4:<host>:<port>
	      Like UDP, but only supports IPv4 protocol.
	      Option groups: FD,SOCKET,IP4

       UDP6:<host>:<port>
	      Like UDP, but only supports IPv6 protocol.
	      Option groups: FD,SOCKET,IP6

       UDP-DATAGRAM:<address>:<port>
	      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 cor-
	      rect remote port and if their source addresses match RANGE or TCPWRAP options. This
	      address  type  can  for  example	be  used for implementing symmetric or asymmetric
	      broadcast or multicast communications.
	      Option groups: FD,SOCKET,IP4,IP6,RANGE
	      Useful options:  bind,  range,  tcpwrap,	broadcast,  ip-multicast-loop,	ip-multi-
	      cast-ttl, ip-multicast-if, ip-add-membership, ttl, tos, sourceport, pf
	      See   also:   UDP4-DATAGRAM,  UDP6-DATAGRAM,  UDP-SENDTO,  UDP-RECVFROM,	UDP-RECV,
	      UDP-CONNECT, UDP-LISTEN, IP-DATAGRAM

       UDP4-DATAGRAM:<address>:<port>
	      Like UDP-DATAGRAM, but only supports IPv4 protocol (example1, example2).
	      Option groups: FD,SOCKET,IP4, RANGE

       UDP6-DATAGRAM:<address>:<port>
	      Like UDP-DATAGRAM, but only supports IPv6 protocol.
	      Option groups: FD,SOCKET,IP6,RANGE

       UDP-LISTEN:<port>
	      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.
	      Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,IP6
	      Useful options: fork, bind, range, pf
	      See also: UDP, UDP4-LISTEN, UDP6-LISTEN, TCP-LISTEN

       UDP4-LISTEN:<port>
	      Like UDP-LISTEN, but only support IPv4 protocol.
	      Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4

       UDP6-LISTEN:<port>
	      Like UDP-LISTEN, but only support IPv6 protocol.
	      Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP6

       UDP-SENDTO:<host>:<port>
	      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 specifica-
	      tion, 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.
	      Option groups: FD,SOCKET,IP4,IP6
	      Useful options: ttl, tos, bind, sourceport, pf
	      See also: UDP4-SENDTO, UDP6-SENDTO, UDP-RECVFROM, UDP-RECV,  UDP-CONNECT,  UDP-LIS-
	      TEN, IP-SENDTO

       UDP4-SENDTO:<host>:<port>
	      Like UDP-SENDTO, but only supports IPv4 protocol.
	      Option groups: FD,SOCKET,IP4

       UDP6-SENDTO:<host>:<port>
	      Like UDP-SENDTO, but only supports IPv6 protocol.
	      Option groups: FD,SOCKET,IP6

       UDP-RECVFROM:<port>
	      Creates  a UDP socket on <port> [UDP service] using UDP/IP version 4 or 6 depending
	      on option pf.  It receives one packet from an unspecified peer and may send one  or
	      more answer packets to that peer. This mode is particularly useful with fork option
	      where each arriving packet - from arbitrary peers -  is  handled	by  its  own  sub
	      process.	This allows a behaviour similar to typical UDP based servers like ntpd or
	      named. This address works well with socat UDP-SENDTO address peers.
	      Option groups: FD,SOCKET,IP4,IP6,CHILD,RANGE
	      Useful options: fork, ttl, tos, bind, sourceport, pf
	      See also: UDP4-RECVFROM, UDP6-RECVFROM, UDP-SENDTO, UDP-RECV, UDP-CONNECT, UDP-LIS-
	      TEN, IP-RECVFROM, UNIX-RECVFROM

       UDP4-RECVFROM:<port>
	      Like UDP-RECVFROM, but only supports IPv4 protocol.
	      Option groups: FD,SOCKET,IP4,CHILD,RANGE

       UDP6-RECVFROM:<port>
	      Like UDP-RECVFROM, but only supports IPv6 protocol.
	      Option groups: FD,SOCKET,IP6,CHILD,RANGE

       UDP-RECV:<port>
	      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.
	      Option groups: FD,SOCKET,IP4,IP6,RANGE
	      Useful options: fork, pf, bind, sourceport, ttl, tos
	      See also: UDP4-RECV, UDP6-RECV, UDP-SENDTO, UDP-RECVFROM, UDP-CONNECT,  UDP-LISTEN,
	      IP-RECV, UNIX-RECV

       UDP4-RECV:<port>
	      Like UDP-RECV, but only supports IPv4 protocol.
	      Option groups: FD,SOCKET,IP4,RANGE

       UDP6-RECV:<port>
	      Like UDP-RECV, but only supports IPv6 protocol.
	      Option groups: FD,SOCKET,IP6,RANGE

       UNIX-CONNECT:<filename>
	      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.
	      Option groups: FD,SOCKET,NAMED,RETRY,UNIX
	      ) Useful options: bind
	      See also: UNIX-LISTEN, UNIX-SENDTO, TCP

       UNIX-LISTEN:<filename>
	      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 con-
	      nects.  Beginning with socat version 1.4.3, the file system entry is  removed  when
	      this address is closed (but see option unlink-close) (example).
	      Option groups: FD,SOCKET,NAMED,LISTEN,CHILD,RETRY,UNIX
	      Useful options: fork, umask, mode, user, group, unlink-early
	      See also: UNIX-CONNECT, UNIX-RECVFROM, UNIX-RECV, TCP-LISTEN

       UNIX-SENDTO:<filename>
	      Communicates with the specified peer socket, defined by [<filename>] assuming it is
	      a UNIX domain datagram socket.  It sends packets to and receives packets from  that
	      peer socket only.  Please note that it might be neccessary to bind the local socket
	      to an address (e.g. /tmp/sock1, which must not exist before).   This  address  type
	      works well with socat UNIX-RECVFROM and UNIX-RECV address peers.
	      Option groups: FD,SOCKET,NAMED,UNIX
	      Useful options: bind
	      See also: UNIX-RECVFROM, UNIX-RECV, UNIX-CONNECT, UDP-SENDTO, IP-SENDTO

       UNIX-RECVFROM:<filename>
	      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.
	      Option groups: FD,SOCKET,NAMED,CHILD,UNIX
	      Useful options: fork
	      See also: UNIX-SENDTO, UNIX-RECV, UNIX-LISTEN, UDP-RECVFROM, IP-RECVFROM

       UNIX-RECV:<filename>
	      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
	      See also: UNIX-SENDTO, UNIX-RECVFROM, UNIX-LISTEN, UDP-RECV, IP-RECV

       UNIX-CLIENT:<filename>
	      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.
	      Option groups: FD,SOCKET,NAMED,UNIX
	      Useful options: bind
	      See also: UNIX-CONNECT, UNIX-SENDTO, GOPEN

       ABSTRACT-CONNECT:<string>

       ABSTRACT-LISTEN:<string>

       ABSTRACT-SENDTO:<string>

       ABSTRACT-RECVFROM:<string>

       ABSTRACT-RECV:<string>

       ABSTRACT-CLIENT:<string>
	      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 "\0"
	      internally. This feature is available (only?) on Linux.  Option groups are the same
	      as with the related UNIX addresses, except that the ABSTRACT addresses are not mem-
	      ber of the NAMED group.

ADDRESS OPTIONS
       Address options can be applied to address specifications to influence the process of open-
       ing the addresses and the properties of the resulting data channels.

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

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

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

       If  the	same  option  is  specified more than once within one address specification, with
       equal or different values, the effect depends on the kind of option. Options resulting  in
       function calls like setsockopt() cause multiple invocations. With options that set parame-
       ters for a required call like open() or set internal flags, the value of the  last  option
       occurrence is effective.

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

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

       FD option group

       This option group contains options that are applied to a UN*X style  file  descriptor,  no
       matter  how it was generated.  Because all current socat address types are file descriptor
       based, these options may be applied to any address.
       Note: Some of these options are also member of another  option  group,  that  provides  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  pri-
       oritized.

       cloexec=<bool>
	      Sets  the FD_CLOEXEC flag with the fcntl() system call to value <bool>. If set, the
	      file descriptor is closed on exec() family function calls. Socat internally handles
	      this  flag for the fds it controls, so in most cases there will be no need to apply
	      this option.

       setlk  Tries to set a discretionary write lock to  the  whole  file  using  the	fcntl(fd,
	      F_SETLK,	...)  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.

       setlkw Tries to set a discretionary waiting  write  lock  to  the  whole  file  using  the
	      fcntl(fd,  F_SETLKW,  ...)   system  call. If the file is already locked, this call
	      blocks.  See option setlk for information about making this lock mandatory.

       setlk-rd
	      Tries to set a discretionary read lock  to  the  whole  file  using  the	fcntl(fd,
	      F_SETLK,	...)  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.

       setlkw-rd
	      Tries to set a discretionary  waiting  read  lock  to  the  whole  file  using  the
	      fcntl(fd,  F_SETLKW,  ...)   system call. If the file is already write locked, this
	      call blocks.  See option setlk for information about making this lock mandatory.

       flock-ex
	      Tries to set a blocking exclusive advisory lock to the  file  using  the	flock(fd,
	      LOCK_EX)	system	call.  Socat  hangs in this call if the file is locked by another
	      process.

       flock-ex-nb
	      Tries to set a nonblocking exclusive advisory lock to the file using the	flock(fd,
	      LOCK_EX|LOCK_NB) system call. If the file is already locked, this option results in
	      an error.

       flock-sh
	      Tries to set a blocking shared advisory  lock  to  the  file  using  the	flock(fd,
	      LOCK_SH)	system	call.  Socat  hangs in this call if the file is locked by another
	      process.

       flock-sh-nb
	      Tries to set a nonblocking shared advisory lock to the  file  using  the	flock(fd,
	      LOCK_SH|LOCK_NB) system call. If the file is already locked, this option results in
	      an error.

       lock   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.

       user=<user>
	      Sets the <user> (owner) of the stream.  If the  address  is  member  of  the  NAMED
	      option  group, socat uses the chown() system call after opening the file or binding
	      to the UNIX domain socket (race condition!).  Without filesystem entry, socat  sets
	      the  user  of the stream using the fchown() system call.	These calls might require
	      root privilege.

       user-late=<user>
	      Sets the owner of the fd to <user> with the fchown() system call after  opening  or
	      connecting the channel.  This is useful only on file system entries.

       group=<group>
	      Sets  the  <group>  of  the  stream.   If the address is member of the NAMED option
	      group, socat uses the chown() system call after opening the file or binding to  the
	      UNIX  domain  socket  (race  condition!).  Without filesystem entry, socat sets the
	      group of the stream with the fchown() system call.  These calls might require group
	      membership or root privilege.

       group-late=<group>
	      Sets  the group of the fd to <group> with the fchown() system call after opening or
	      connecting the channel.  This is useful only on file system entries.

       mode=<mode>
	      Sets the <mode> [mode_t] (permissions) of the stream.  If the address is member  of
	      the  NAMED  option  group  and uses the open() or creat() call, the mode is applied
	      with these.  If the address is member of the NAMED option group without using these
	      system calls, socat uses the chmod() system call after opening the filesystem entry
	      or binding to the UNIX domain socket (race condition!).  Otherwise, socat sets  the
	      mode  of	the  stream using fchmod() .  These calls might require ownership or root
	      privilege.

       perm-late=<mode>
	      Sets the permissions of the fd to value <mode> [mode_t] using the  fchmod()  system
	      call  after  opening or connecting the channel.  This is useful only on file system
	      entries.

       append=<bool>
	      Always writes data to the actual end of file.  If the address is member of the OPEN
	      option  group,  socat uses the O_APPEND flag with the open() system call (example).
	      Otherwise, socat applies the fcntl(fd, F_SETFL, O_APPEND) call.

       nonblock=<bool>
	      Tries to open or use file in nonblocking mode. Its only effects are that	the  con-
	      nect()  call  of	TCP  addresses	does not block, and that opening a named pipe for
	      reading does not block.  If the address is member of the OPEN option  group,  socat
	      uses the O_NONBLOCK flag with the open() system call.  Otherwise, socat applies the
	      fcntl(fd, F_SETFL, O_NONBLOCK) call.

       binary Opens the file in binary mode to avoid implicit line terminator  conversions  (Cyg-
	      win).

       text   Opens the file in text mode to force implicit line terminator conversions (Cygwin).

       noinherit
	      Does not keep this file open in a spawned process (Cygwin).

       cool-write
	      Takes  it  easy when write fails with EPIPE or ECONNRESET and logs the message with
	      notice level instead of error.  This prevents the log file from being  filled  with
	      useless  error  messages	when socat is used as a high volume server or proxy where
	      clients often abort the connection.
	      This option is experimental.

       end-close
	      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).
	      Normally, socket connections will be ended with shutdown(2)  which  terminates  the
	      socket  even  if it is shared by multiple processes.  close(2) "unlinks" the socket
	      from the process but keeps it active as long as there are still  links  from  other
	      processes.
	      Similarly,  when	an  address  of  type EXEC or SYSTEM is ended, socat usually will
	      explicitely kill the sub process. With this option, it will  just  close	the  file
	      descriptors.

       shut-none
	      Changes the (address dependent) method of shutting down the write part of a connec-
	      tion to not do anything.

       shut-down
	      Changes the (address dependent) method of shutting down the write part of a connec-
	      tion to shutdown\(fd, SHUT_WR). Is only useful with sockets.

       shut-close
	      Changes the (address dependent) method of shutting down the write part of a connec-
	      tion to close\(fd).

       shut-null
	      When one address indicates EOF, socat will send a zero sized packet  to  the  write
	      channel of the other address to transfer the EOF condition. This is useful with UDP
	      and other datagram protocols. Has been tested against netcat and socat with  option
	      null-eof.

       null-eof
	      Normally	socat  will ignore empty (zero size payload) packets arriving on datagram
	      sockets, so it survives port scans. With this option socat interprets  empty  data-
	      gram packets as EOF indicator (see shut-null).

       ioctl-void=<request>
	      Calls ioctl() with the request value as second argument and NULL as third argument.
	      This option allows to utilize ioctls that are not explicitely implemented in socat.

       ioctl-int=<request>:<value>
	      Calls ioctl() with the request value as second argument and the  integer	value  as
	      third argument.

       ioctl-intp=<request>:<value>
	      Calls  ioctl() with the request value as second argument and a pointer to the inte-
	      ger value as third argument.

       ioctl-bin=<request>:<value>
	      Calls ioctl() with the request value as second argument and a pointer to the  given
	      data value as third argument. This data must be specified in <dalan> form.

       ioctl-string=<request>:<value>
	      Calls  ioctl() with the request value as second argument and a pointer to the given
	      string as third argument.  <dalan> form.

       NAMED option group

       These options work on file system entries.
       See also options user, group, and mode.

       user-early=<user>
	      Changes the <user> (owner) of the file system entry before accessing it, using  the
	      chown() system call. This call might require root privilege.

       group-early=<group>
	      Changes the <group> of the file system entry before accessing it, using the chown()
	      system call. This call might require group membership or root privilege.

       perm-early=<mode>
	      Changes the <mode> [mode_t] of the file system entry before accessing it, using the
	      chmod() system call. This call might require ownership or root privilege.

       umask=<mode>
	      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 opera-
	      tions of the socat process!

       unlink-early
	      Unlinks  (removes)  the  file before opening it and even before applying user-early
	      etc.

       unlink Unlinks (removes) the file before accessing it, but after user-early etc.

       unlink-late
	      Unlinks (removes) the file after opening it to make it inaccessible for other  pro-
	      cesses after a short race condition.

       unlink-close
	      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.

       OPEN option group

       The OPEN group options allow to set flags with  the  open()  system  call.   E.g.,  option
       `creat' sets the O_CREAT flag.
       See also options append and nonblock.

       creat=<bool>
	      Creates the file if it does not exist (example).

       dsync=<bool>
	      Blocks write() calls until metainfo is physically written to media.

       excl=<bool>
	      With option creat, if file exists this is an error.

       largefile=<bool>
	      On 32 bit systems, allows a file larger than 2^31 bytes.

       noatime
	      Sets the O_NOATIME options, so reads do not change the access timestamp.

       noctty=<bool>
	      Does not make this file the controlling terminal.

       nofollow=<bool>
	      Does not follow symbolic links.

       nshare=<bool>
	      Does not allow to share this file with other processes.

       rshare=<bool>
	      Does not allow other processes to open this file for writing.

       rsync=<bool>
	      Blocks write() until metainfo is physically written to media.

       sync=<bool>
	      Blocks write() until data is physically written to media.

       rdonly=<bool>
	      Opens the file for reading only.

       wronly=<bool>
	      Opens the file for writing only.

       trunc  Truncates the file to size 0 during opening it.

       REG and BLK option group

       These  options  are  usually  applied  to a UN*X file descriptor, but their semantics make
       sense only on a file supporting random access.

       seek=<offset>
	      Applies the lseek(fd, <offset>, SEEK_SET) (or lseek64 ) system call, thus position-
	      ing  the file pointer absolutely to <offset> [off_t or off64_t]. Please note that a
	      missing value defaults to 1, not 0.

       seek-cur=<offset>
	      Applies the lseek(fd, <offset>, SEEK_CUR) (or lseek64 ) system call, thus position-
	      ing  the	file  pointer <offset> [off_t or off64_t] bytes relatively to its current
	      position (which is usually 0). Please note that a missing value defaults to 1,  not
	      0.

       seek-end=<offset>
	      Applies the lseek(fd, <offset>, SEEK_END) (or lseek64 ) system call, thus position-
	      ing the file pointer <offset> [off_t or off64_t] bytes relatively to the files cur-
	      rent end. Please note that a missing value defaults to 1, not 0.

       ftruncate=<offset>
	      Applies the ftruncate(fd, <offset>) (or ftruncate64 if available) system call, thus
	      truncating the file at the position <offset> [off_t or off64_t]. Please note that a
	      missing value defaults to 1, not 0.

       secrm=<bool>

       unrm=<bool>

       compr=<bool>

       ext2-sync=<bool>

       immutable=<bool>

       ext2-append=<bool>

       nodump=<bool>

       ext2-noatime=<bool>

       journal-data=<bool>

       notail=<bool>

       dirsync=<bool>
	      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.

       PROCESS option group

       Options of this group change the process properties instead of  just  affecting	one  data
       channel.   For  EXEC  and  SYSTEM addresses and for LISTEN and CONNECT type addresses with
       option FORK, these options apply to the child processes instead of the main socat process.

       chroot=<directory>
	      Performs a chroot() operation to <directory> after processing  the  address  (exam-
	      ple). This call might require root privilege.

       chroot-early=<directory>
	      Performs	a chroot() operation to <directory> before opening the address. This call
	      might require root privilege.

       setgid=<group>
	      Changes the primary <group> of the process after processing the address. This  call
	      might  require  root  privilege.	Please	note that this option does not drop other
	      group related privileges.

       setgid-early=<group>
	      Like setgit but is performed before opening the address.

       setuid=<user>
	      Changes the <user> (owner) of the process after processing the address.  This  call
	      might  require  root  privilege.	Please	note that this option does not drop group
	      related privileges. Check if option su better fits your needs.

       setuid-early=<user>
	      Like setuid but is performed before opening the address.

       su=<user>
	      Changes the <user> (owner) and groups of the process after processing  the  address
	      (example). This call might require root privilege.

       su-d=<user>
	      Short  name  for	substuser-delayed.   Changes the <user> (owner) and groups of the
	      process after processing the address  (example).	 The  user  and  his  groups  are
	      retrieved before a possible chroot() . This call might require root privilege.

       setpgid=<pid_t>
	      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.

       setsid Makes the process the leader of a new session (example).

       READLINE option group

       These options apply to the readline address type.

       history=<filename>
	      Reads and writes history from/to <filename> (example).

       noprompt
	      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  out-
	      put.  With this option, socat does not pass a prompt to readline, so it begins line
	      editing in the first column of the terminal.

       noecho=<pattern>
	      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)

       prompt=<string>
	      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.

       APPLICATION option group

       This group contains options that work at data level.  Note that these options  only  apply
       to  the	"raw"  data transferred by socat, but not to protocol data used by addresses like
       PROXY.

       cr     Converts the default line termination character NL ('\n', 0x0a) to/from  CR  ('\r',
	      0x0d) when writing/reading on this channel.

       crnl   Converts	the  default  line  termination  character  NL	('\n', 0x0a) to/from CRNL
	      ("\r\n", 0x0d0a) when writing/reading on this channel (example).	Note: socat  sim-
	      ply strips all CR characters.

       ignoreeof
	      When EOF occurs on this channel, socat ignores it and tries to read more data (like
	      "tail -f") (example).

       readbytes=<bytes>
	      socat reads only so many bytes from this address (the address provides only so many
	      bytes for transfer and pretends to be at EOF afterwards).  Must be greater than 0.

       lockfile=<filename>
	      If  lockfile  exists,  exits with error. If lockfile does not exist, creates it and
	      continues, unlinks lockfile on exit.

       waitlock=<filename>
	      If lockfile exists, waits until it disappears. When lockfile does not  exist,  cre-
	      ates it and continues, unlinks lockfile on exit.

       escape=<int>
	      Specifies the numeric code of a character that triggers EOF on the input stream. It
	      is useful with a terminal in raw mode (example).

       SOCKET option group

       These options are intended for all kinds of sockets, e.g. IP  or  UNIX  domain.	Most  are
       applied with a setsockopt() call.

       bind=<sockname>
	      Binds the socket to the given socket address using the bind() system call. The form
	      of <sockname> is socket domain  dependent:  IP4  and  IP6  allow	the  form  [host-
	      name|hostaddress][:(service|port)]  (example),  UNIX  domain sockets require <file-
	      name>.

       connect-timeout=<seconds>
	      Abort the connection attempt after <seconds> [timeval] with error status.

       so-bindtodevice=<interface>
	      Binds the socket to the given <interface>.  This option might require  root  privi-
	      lege.

       broadcast
	      For  datagram  sockets, allows sending to broadcast addresses and receiving packets
	      addressed to broadcast addresses.

       debug  Enables socket debugging.

       dontroute
	      Only communicates with directly connected peers, does not use routers.

       keepalive
	      Enables sending keepalives on the socket.

       linger=<seconds>
	      Blocks shutdown() or close() until data transfers have finished or the given  time-
	      out [int] expired.

       oobinline
	      Places out-of-band data in the input data stream.

       priority=<priority>
	      Sets the protocol defined <priority> [<int>] for outgoing packets.

       rcvbuf=<bytes>
	      Sets the size of the receive buffer after the socket() call to <bytes> [int].  With
	      TCP sockets, this value corresponds to the socket's maximal window size.

       rcvbuf-late=<bytes>
	      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.

       rcvlowat=<bytes>
	      Specifies the minimum number of received bytes [int] until the  socket  layer  will
	      pass the buffered data to socat.

       rcvtimeo=<seconds>
	      Sets the receive timeout [timeval].

       reuseaddr
	      Allows  other  sockets  to  bind	to an address even if parts of it (e.g. the local
	      port) are already in use by socat (example).

       sndbuf=<bytes>
	      Sets the size of the send buffer after the socket() call to <bytes> [int].

       sndbuf-late=<bytes>
	      Sets the size of the send buffer when the socket is connected to <bytes> [int].

       sndlowat=<bytes>
	      Specifies the minimum number of bytes in the send buffer	until  the  socket  layer
	      will send the data to <bytes> [int].

       sndtimeo=<seconds>
	      Sets the send timeout to seconds [timeval].

       pf=<string>
	      Forces  the  use of the specified IP version or protocol. <string> can be something
	      like "ip4" or "ip6". The resulting value is used as first argument to the  socket()
	      or  socketpair()	calls.	 This  option affects address resolution and the required
	      syntax of bind and range options.

       type=<type>
	      Sets the type of the socket, specified as second argument to the socket() or  sock-
	      etpair() calls, to <type> [int]. Address resolution is not affected by this option.
	      Under Linux, 1 means stream oriented socket, 2 means datagram socket, and  3  means
	      raw socket.

       prototype
	      Sets  the  protocol  of  the socket, specified as third argument to the socket() or
	      socketpair() calls, to <prototype> [int]. Address resolution  is	not  affected  by
	      this option.  6 means TCP, 17 means UDP.

       so-timestamp
	      Sets  the  SO_TIMESTAMP  socket option. This enables receiving and logging of time-
	      stamp ancillary messages.

       setsockopt-int=<level>:<optname>:<optval>
	      Invokes setsockopt() for the socket with the given parameters. level [int] is  used
	      as second argument to setsockopt() and specifies the layer, e.g. SOL_TCP for TCP (6
	      on Linux), or SOL_SOCKET for the socket layer (1 on Linux). optname  [int]  is  the
	      third  argument to setsockopt() and tells which socket option is to be set. For the
	      actual numbers you might have to look up the appropriate include files of your sys-
	      tem.  The  4th  setsockopt()  parameter, value [int], is passed to the function per
	      pointer, and for the length parameter sizeof\(int) is taken implicitely.

       setsockopt-bin=<level>:<optname>:<optval>
	      Like setsockopt-int, but <optval> must be provided in dalan format and specifies an
	      arbitrary sequence of bytes; the length parameter is automatically derived from the
	      data.

       setsockopt-string=<level>:<optname>:<optval>
	      Like setsockopt-int, but <optval> must be a string.  This string is passed  to  the
	      function	with  trailing	null character, and the length parameter is automatically
	      derived from the data.

       UNIX option group

       These options apply to UNIX domain based addresses.

       unix-tightsocklen=[0|1]
	      On socket operations, pass a socket address length that does not include the  whole
	      struct  sockaddr_un record but (besides other components) only the relevant part of
	      the filename or abstract string. Default is 1.

       IP4 and IP6 option groups

       These options can be used with IPv4 and IPv6 based sockets.

       tos=<tos>
	      Sets the TOS (type of service) field of outgoing packets to <tos> [byte]	(see  RFC
	      791).

       ttl=<ttl>
	      Sets the TTL (time to live) field of outgoing packets to <ttl> [byte].

       ip-options=<data>
	      Sets IP options like source routing. Must be given in binary form, recommended for-
	      mat 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 ip-options=x8307040a000001 .
	      IP options are defined in RFC 791.

       mtudiscover=<0|1|2>
	      Takes 0, 1, 2 to never, want, or always use path MTU discover on this socket.

       ip-pktinfo
	      Sets  the IP_PKTINFO socket option. This enables receiving and logging of ancillary
	      messages containing destination address and interface (Linux) (example).

       ip-recverr
	      Sets the IP_RECVERR socket option. This enables receiving and logging of	ancillary
	      messages containing detailled error information.

       ip-recvopts
	      Sets  the  IP_RECVOPTS  socket  option.  This  enables  receiving and logging of IP
	      options ancillary messages (Linux, *BSD).

       ip-recvtos
	      Sets the IP_RECVTOS socket option. This enables receiving and logging of TOS  (type
	      of service) ancillary messages (Linux).

       ip-recvttl
	      Sets  the IP_RECVTTL socket option. This enables receiving and logging of TTL (time
	      to live) ancillary messages (Linux, *BSD).

       ip-recvdstaddr
	      Sets the IP_RECVDSTADDR socket option. This enables receiving and logging of ancil-
	      lary messages containing destination address (*BSD) (example).

       ip-recvif
	      Sets  the  IP_RECVIF socket option. This enables receiving and logging of interface
	      ancillary messages (*BSD) (example).

       ip-add-membership=<multicast-address:interface-address>

       ip-add-membership=<multicast-address:interface-name>

       ip-add-membership=<multicast-address:interface-index>

       ip-add-membership=<multicast-address:interface-address:interface-name>

       ip-add-membership=<multicast-address:interface-address:interface-index>
	      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 struct mreqn (Linux).
	      The indices of active network interfaces can be shown using the utility procan.

       ip-multicast-if=<hostname>
	      Specifies  hostname  or  address	of the network interface to be used for multicast
	      traffic.

       ip-multicast-loop=<bool>
	      Specifies if outgoing multicast traffic should loop back to the interface.

       ip-multicast-ttl=<byte>
	      Sets the TTL used for outgoing multicast traffic. Default is 1.

       res-debug

       res-aaonly

       res-usevc

       res-primary

       res-igntc

       res-recurse

       res-defnames

       res-stayopen

       res-dnsrch
	      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.

       IP6 option group

       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.

       ipv6only=<bool>
	      Sets the IPV6_V6ONLY socket option. If 0, the TCP stack will  also  accept  connec-
	      tions using IPv4 protocol on the same port. The default is system dependent.

       ipv6-recvdstopts
	      Sets  the  IPV6_RECVDSTOPTS  socket  option.  This enables receiving and logging of
	      ancillary messages containing the destination options.

       ipv6-recvhoplimit
	      Sets the IPV6_RECVHOPLIMIT socket option. This enables  receiving  and  logging  of
	      ancillary messages containing the hoplimit.

       ipv6-recvhopopts
	      Sets  the  IPV6_RECVHOPOPTS  socket  option.  This enables receiving and logging of
	      ancillary messages containing the hop options.

       ipv6-recvpktinfo
	      Sets the IPV6_RECVPKTINFO socket option. This  enables  receiving  and  logging  of
	      ancillary messages containing destination address and interface.

       ipv6-unicast-hops=link(TYPE_INT)(<int>)
	      Sets  the  IPV6_UNICAST_HOPS socket option. This sets the hop count limit (TTL) for
	      outgoing unicast packets.

       ipv6-recvrthdr
	      Sets the IPV6_RECVRTHDR socket option. This enables receiving and logging of ancil-
	      lary messages containing routing information.

       ipv6-tclass
	      Sets  the IPV6_TCLASS socket option. This sets the transfer class of outgoing pack-
	      ets.

       ipv6-recvtclass
	      Sets the IPV6_RECVTCLASS socket option.  This  enables  receiving  and  logging  of
	      ancillary messages containing the transfer class.

       TCP option group

       These  options  may be applied to TCP sockets. They work by invoking setsockopt() with the
       appropriate parameters.

       cork   Doesn't send packets smaller than MSS (maximal segment size).

       defer-accept
	      While listening, accepts connections only when data from the peer arrived.

       keepcnt=<count>
	      Sets the number of keepalives before shutting down the socket to <count> [int].

       keepidle=<seconds>
	      Sets the idle time before sending the first keepalive to <seconds> [int].

       keepintvl=<seconds>
	      Sets the interval between two keepalives to <seconds> [int].

       linger2=<seconds>
	      Sets the time to keep the socket in FIN-WAIT-2 state to <seconds> [int].

       mss=<bytes>
	      Sets the MSS (maximum segment size) after the socket() call to <bytes> [int].  This
	      value is then proposed to the peer with the SYN or SYN/ACK packet (example).

       mss-late=<bytes>
	      Sets the MSS of the socket after connection has been established to <bytes> [int].

       nodelay
	      Turns off the Nagle algorithm for measuring the RTT (round trip time).

       rfc1323
	      Enables  RFC1323 TCP options: TCP window scale, round-trip time measurement (RTTM),
	      and protect against wrapped sequence numbers (PAWS) (AIX).

       stdurg Enables RFC1122 compliant urgent pointer handling (AIX).

       syncnt=<count>
	      Sets the maximal number of SYN retransmits during connect to <count> [int].

       md5sig Enables generation of MD5 digests on the packets (FreeBSD).

       noopt  Disables use of TCP options (FreeBSD, MacOSX).

       nopush sets the TCP_NOPUSH socket option (FreeBSD, MacOSX).

       sack-disable
	      Disables use the selective acknowledge feature (OpenBSD).

       signature-enable
	      Enables generation of MD5 digests on the packets (OpenBSD).

       abort-threshold=<milliseconds>
	      Sets the time to wait for an answer  of  the  peer  on  an  established  connection
	      (HP-UX).

       conn-abort-threshold=<milliseconds>
	      Sets  the  time  to  wait  for  an  answer of the server during the initial connect
	      (HP-UX).

       keepinit
	      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).

       paws   Enables the "protect against wrapped sequence numbers" feature (Tru64).

       sackena
	      Enables selective acknowledge (Tru64).

       tsoptena
	      Enables the time stamp option that allows RTT recalculation on existing connections
	      (Tru64).

       SCTP option group

       These options may be applied to SCTP stream sockets.

       sctp-nodelay
	      Sets the SCTP_NODELAY socket option that disables the Nagle algorithm.

       sctp-maxseg=<bytes>
	      Sets the SCTP_MAXSEG socket option to <bytes> [int].  This value is  then  proposed
	      to the peer with the SYN or SYN/ACK packet.

       UDP, TCP, and SCTP option groups

       Here  we  find options that are related to the network port mechanism and thus can be used
       with UDP, TCP, and SCTP client and server addresses.

       sourceport=<port>
	      For outgoing (client) TCP and UDP connections, it sets the source <port>	using  an
	      extra  bind() call.  With TCP or UDP listen addresses, socat immediately shuts down
	      the connection if the client does not use this sourceport (example).

       lowport
	      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.

       SOCKS option group

       When using SOCKS type addresses, some socks specific options can be set.

       socksport=<tcp service>
	      Overrides  the  default "socks" service or port 1080 for the socks server port with
	      <TCP service>.

       socksuser=<user>
	      Sends the <user> [string] in the username field to the socks server. Default is the
	      actual user name ($LOGNAME or $USER) (example).

       HTTP option group

       Options	that  can  be  provided with HTTP type addresses. The only HTTP address currently
       implemented is proxy-connect.

       proxyport=<TCP service>
	      Overrides the default HTTP proxy port 8080 with <TCP service>.

       ignorecr
	      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. Neverthe-
	      less, socat sends CR+NL to the proxy.

       proxyauth=<username>:<password>
	      Provide  "basic"	authentication to the proxy server. The argument to the option is
	      used with a "Proxy-Authorization: Base" header in base64 encoded form.
	      Note: username and password are visible for every user on the local machine in  the
	      process list; username and password are transferred to the proxy server unencrypted
	      (base64 encoded) and might be sniffed.

       resolve
	      Per default, socat sends to the proxy a CONNECT request containing the target host-
	      name.  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.

       RANGE option group

       These  options  check if a connecting client should be granted access. They can be applied
       to listening and receiving network sockets. tcp-wrappers options fall into this group.

       range=<address-range>
	      After accepting a  connection,  tests  if  the  peer  is	within	range.	For  IPv4
	      addresses,   address-range  takes  the  form  address/bits,  e.g.   10.0.0.0/8,  or
	      address:mask,   e.g.   10.0.0.0:255.0.0.0    (example);	 for	IPv6,	 it    is
	      [ip6-address/bits],  e.g.  [::1/128].   If the client address does not match, socat
	      issues a warning and keeps listening/receiving.

       tcpwrap[=<name>]
	      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.

       allow-table=<filename>
	      Takes the specified file instead of /etc/hosts.allow.

       deny-table=<filename>
	      Takes the specified file instead of /etc/hosts.deny.

       tcpwrap-etc=<directoryname>
	      Looks for hosts.allow and hosts.deny in the specified directory. Is  overridden  by
	      options hosts-allow and hosts-deny.

       LISTEN option group

       Options specific to listening sockets.

       backlog=<count>
	      Sets  the  backlog  value  passed  with  the listen() system call to <count> [int].
	      Default is 5.

       max-children=<count>
	      Limits the number of concurrent child processes [int].  Default is no limit.

       CHILD option group

       Options for addresses with multiple connections via child processes.

       fork   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).
	      SSL-CONNECT and SSL-LISTEN differ  in  when  they  actually  fork  off  the  child:
	      SSL-LISTEN  forks  before  the  SSL  handshake, while SSL-CONNECT forks afterwards.
	      RETRY and FOREVER options are not inherited by the child process.

       EXEC option group

       Options for addresses that invoke a program.

       path=<string>
	      Overrides the PATH environment variable for searching the  program  with	<string>.
	      This $PATH value is effective in the child process too.

       login  Prefixes	argv[0]  for  the  execvp()  call with '-', thus making a shell behave as
	      login shell.

       FORK option group

       EXEC or SYSTEM addresses invoke a program using a child process and transfer data  between
       socat and the program. The interprocess communication mechanism can be influenced with the
       following options. Per default, a socketpair() is created and assigned to stdin and stdout
       of  the	child  process,  while	stderr is inherited from the socat process, and the child
       process uses file descriptors 0 and 1 for communicating with the main socat process.

       nofork 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  restric-
	      tions:

       o      this option can only be applied to the second socat address.

       o      it cannot be applied to a part of a dual address.

       o      the first socat address cannot be OPENSSL or READLINE

       o      socat options -b, -t, -D, -l, -v, -x become useless

       o      for both addresses, options ignoreeof, cr, and crnl become useless

       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.

       pipes  Creates  a pair of unnamed pipes for interprocess communication instead of a socket
	      pair.

       openpty
	      Establishes communication with the sub process using a pseudo terminal created with
	      openpty() instead of the default (socketpair or ptmx).

       ptmx   Establishes  communication  with the sub process using a pseudo terminal created by
	      opening /dev/ptmx or /dev/ptc instead of the default (socketpair).

       pty    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).

       ctty   Makes the pty the controlling tty of the sub process (example).

       stderr Directs stderr of the sub process to its output channel by making stderr a dup() of
	      stdout (example).

       fdin=<fdnum>
	      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 socat (example).

       fdout=<fdnum>
	      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 socat (example).

       sighup, sigint, sigquit
	      Has  socat  pass	signals  of this type to the sub process.  If no address has this
	      option, socat terminates on these signals.

       TERMIOS option group

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

       b0     Disconnects the terminal.

       b19200 Sets  the serial line speed to 19200 baud. Some other rates are possible; use some-
	      thing like socat -hh |grep ' b[1-9]' to find all speeds supported by your implemen-
	      tation.
	      Note:  On some operating systems, these options may not be available. Use ispeed or
	      ospeed instead.

       echo=<bool>
	      Enables or disables local echo (example).

       icanon=<bool>
	      Sets or clears canonical mode, enabling line buffering and some special characters.

       raw    Sets raw mode, thus passing input and output almost unprocessed (example).

       ignbrk=<bool>
	      Ignores or interpretes the BREAK character (e.g., ^C)

       brkint=<bool>

       bs0

       bs1

       bsdly=<0|1>

       clocal=<bool>

       cr0
       cr1
       cr2
       cr3

	      Sets the carriage return delay to 0, 1, 2, or 3, respectively.  0 means  no  delay,
	      the other values are terminal dependent.

       crdly=<0|1|2|3>

       cread=<bool>

       crtscts=<bool>

       cs5
       cs6
       cs7
       cs8

	      Sets the character size to 5, 6, 7, or 8 bits, respectively.

       csize=<0|1|2|3>

       cstopb=<bool>
	      Sets two stop bits, rather than one.

       dsusp=<byte>
	      Sets  the  value	for  the  VDSUSP  character  that suspends the current foreground
	      process and reactivates the shell (all except Linux).

       echoctl=<bool>
	      Echos control characters in hat notation (e.g. ^A)

       echoe=<bool>

       echok=<bool>

       echoke=<bool>

       echonl=<bool>

       echoprt=<bool>

       eof=<byte>

       eol=<byte>

       eol2=<byte>

       erase=<byte>

       discard=<byte>

       ff0

       ff1

       ffdly=<bool>

       flusho=<bool>

       hupcl=<bool>

       icrnl=<bool>

       iexten=<bool>

       igncr=<bool>

       ignpar=<bool>

       imaxbel=<bool>

       inlcr=<bool>

       inpck=<bool>

       intr=<byte>

       isig=<bool>

       ispeed=<unsigned-int>
	      Set the baud rate for incoming data on this line.
	      See also: ospeed, b19200

       istrip=<bool>

       iuclc=<bool>

       ixany=<bool>

       ixoff=<bool>

       ixon=<bool>

       kill=<byte>

       lnext=<byte>

       min=<byte>

       nl0    Sets the newline delay to 0.

       nl1

       nldly=<bool>

       noflsh=<bool>

       ocrnl=<bool>

       ofdel=<bool>

       ofill=<bool>

       olcuc=<bool>

       onlcr=<bool>

       onlret=<bool>

       onocr=<bool>

       opost=<bool>
	      Enables or disables output processing; e.g., converts NL to CR-NL.

       ospeed=<unsigned-int>
	      Set the baud rate for outgoing data on this line.
	      See also: ispeed, b19200

       parenb=<bool>
	      Enable parity generation on output and parity checking for input.

       parmrk=<bool>

       parodd=<bool>

       pendin=<bool>

       quit=<byte>

       reprint=<byte>

       sane   Brings the terminal to something like a useful default state.

       start=<byte>

       stop=<byte>

       susp=<byte>

       swtc=<byte>

       tab0

       tab1

       tab2

       tab3

       tabdly=<unsigned-int>

       time=<byte>

       tostop=<bool>

       vt0

       vt1

       vtdly=<bool>

       werase=<byte>

       xcase=<bool>

       xtabs

       i-pop-all
	      With UNIX System V STREAMS, removes all drivers from the stack.

       i-push=<string>
	      With UNIX System V STREAMS, pushes the driver (module) with the given name (string)
	      onto  the  stack. For example, to make sure that a character device on Solaris sup-
	      ports	  termios	etc,	   use	     the	following	 options:
	      i-pop-all,i-push=ptem,i-push=ldterm,i-push=ttcompat

       PTY option group

       These options are intended for use with the pty address type.

       link=<filename>
	      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  unpre-
	      dictable	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 socat
	      version 1.4.3, the symbolic link is removed when the address  is	closed	(but  see
	      option unlink-close).

       wait-slave
	      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  poll() 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.

       pty-interval=<seconds>
	      When  the  wait-slave  option  is  set, socat periodically checks the HUP condition
	      using poll() to find if the pty's slave side has been opened. The  default  polling
	      interval is 1s. Use the pty-interval option [timeval] to change this value.

       OPENSSL option group

       These options apply to the openssl and openssl-listen address types.

       cipher=<cipherlist>
	      Selects  the list of ciphers that may be used for the connection.  See the man page
	      of ciphers , section CIPHER LIST FORMAT, for  detailed  information  about  syntax,
	      values, and default of <cipherlist>.
	      Several cipher strings may be given, separated by ':'.  Some simple cipher strings:

       3DES   Uses a cipher suite with triple DES.

       MD5    Uses a cipher suite with MD5.

       aNULL  Uses a cipher suite without authentication.

       NULL   Does not use encryption.

       HIGH   Uses  a  cipher  suite with "high" encryption.  Note that the peer must support the
	      selected property, or the negotiation will fail.

       method=<ssl-method>
	      Sets the protocol version to be used. Valid strings (not case sensitive) are:

       SSLv2  Select SSL protocol version 2.

       SSLv3  Select SSL protocol version 3.

       SSLv23 Select SSL protocol version 2 or 3. This is the default when  this  option  is  not
	      provided.

       TLSv1  Select TLS protocol version 1.

       verify=<bool>
	      Controls	check  of  the	peer's certificate. Default is 1 (true). Disabling verify
	      might open your socket for everyone, making the encryption useless!

       cert=<filename>
	      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.

       key=<filename>
	      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.

       dhparams=<filename>
	      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.

       cafile=<filename>
	      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.

       capath=<dirname>
	      Specifies  the  directory  with the trusted (root) certificates. The directory must
	      contain certificates in PEM format and their hashes (see OpenSSL documentation)

       egd=<filename>
	      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.

       pseudo On systems where openssl cannot find an entropy source and where no entropy gather-
	      ing  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.
	      NOTE:This mechanism is not sufficient for generation of secure keys!

       compress
	      Enable or disable the use of compression for a connection. Setting this  to  "none"
	      disables	compression,  setting it to "auto" lets OpenSSL choose the best available
	      algorithm supported by both parties. The default	is  to	not  touch  any  compres-
	      sion-related  settings.	NOTE: Requires OpenSSL 0.9.8 or higher and disabling com-
	      pression with OpenSSL 0.9.8 affects all new connections in the process.

       fips   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.

       RETRY option group

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

       retry=<num>
	      Number of retries before the connection or listen attempt is aborted.   Default  is
	      0, which means just one attempt.

       interval=<timespec>
	      Time between consecutive attempts (seconds, [timespec]). Default is 1 second.

       forever
	      Performs an unlimited number of retry attempts.

       TUN option group

       Options that control Linux TUN/TAP interface device addresses.

       tun-device=<device-file>
	      Instructs  socat	to  take  another  path  for  the  TUN	clone  device. Default is
	      /dev/net/tun.

       tun-name=<if-name>
	      Gives the resulting network interface a specific name instead of the system  gener-
	      ated (tun0, tun1, etc.)

       tun-type=[tun|tap]
	      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.

       iff-no-pi
	      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.

       iff-up Sets the TUN network interface status UP. Strongly recommended.

       iff-broadcast
	      Sets the BROADCAST flag of the TUN network interface.

       iff-debug
	      Sets the DEBUG flag of the TUN network interface.

       iff-loopback
	      Sets the LOOPBACK flag of the TUN network interface.

       iff-pointopoint
	      Sets the POINTOPOINT flag of the TUN device.

       iff-notrailers
	      Sets the NOTRAILERS flag of the TUN device.

       iff-running
	      Sets the RUNNING flag of the TUN device.

       iff-noarp
	      Sets the NOARP flag of the TUN device.

       iff-promisc
	      Sets the PROMISC flag of the TUN device.

       iff-allmulti
	      Sets the ALLMULTI flag of the TUN device.

       iff-master
	      Sets the MASTER flag of the TUN device.

       iff-slave
	      Sets the SLAVE flag of the TUN device.

       iff-multicast
	      Sets the MULTICAST flag of the TUN device.

       iff-portsel
	      Sets the PORTSEL flag of the TUN device.

       iff-automedia
	      Sets the AUTOMEDIA flag of the TUN device.

       iff-dynamic
	      Sets the DYNAMIC flag of the TUN device.

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

       address-range
	      Is currently only implemented for IPv4 and IPv6. See address-option `range'

       bool   "0" or "1"; if value is omitted, "1" is taken.

       byte   An unsigned int number, read with strtoul() , lower or equal to UCHAR_MAX .

       command-line
	      A string specifying a program name and its arguments, separated by single spaces.

       data   A raw data specification following dalan syntax. Currently the only valid form is a
	      string  starting	with  'x'  followed by an even number of hex digits, specifying a
	      sequence of bytes.

       directory
	      A string with usual UN*X directory name semantics.

       facility
	      The name of a syslog facility in lower case characters.

       fdnum  An unsigned int type, read with strtoul() , specifying a UN*X file descriptor.

       filename
	      A string with usual UN*X filename semantics.

       group  If the first character is a decimal digit, the value  is	read  with  strtoul()  as
	      unsigned	integer  specifying  a	group id. Otherwise, it must be an existing group
	      name.

       int    A number following the rules of the strtol() 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.

       interface
	      A string specifying the device name of a network interface as shown by ifconfig  or
	      procan, e.g. "eth0".

       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.
	      Examples: 127.0.0.1, [::1], www.dest-unreach.org, dns1

       IPv4 address
	      An IPv4 address in numbers-and-dots notation or a hostname that resolves to an IPv4
	      address.
	      Examples: 127.0.0.1, www.dest-unreach.org, dns2

       IPv6 address
	      An  iPv6 address in hexnumbers-and-colons notation enclosed in brackets, or a host-
	      name that resolves to an IPv6 address.
	      Examples: [::1], [1234:5678:9abc:def0:1234:5678:9abc:def0], ip6name.domain.org

       long   A number read with strtol() . The value must fit into a C long.

       long long
	      A number read with strtoll() . The value must fit into a C long long.

       off_t  An implementation dependend signed number, usually 32 bits,  read  with  strtol  or
	      strtoll.

       off64_t
	      An  implementation  dependend  signed  number, usually 64 bits, read with strtol or
	      strtoll.

       mode_t An unsigned integer, read with strtoul() , specifying mode (permission) bits.

       pid_t  A number, read with strtol() , specifying a process id.

       port   A uint16_t (16 bit unsigned number) specifying a TCP or UDP port,  read  with  str-
	      toul() .

       protocol
	      An unsigned 8 bit number, read with strtoul() .

       size_t An unsigned number with size_t limitations, read with strtoul .

       sockname
	      A socket address. See address-option `bind'

       string A sequence of characters, not containing '\0' and, depending on the position within
	      the command line, ':', ',', or "!!". Note that you might have to escape shell  meta
	      characters in the command line.

       TCP service
	      A service name, not starting with a digit, that is resolved by getservbyname() , or
	      an unsigned int 16 bit number read with strtoul() .

       timeval
	      A double float specifying seconds; the number is mapped into a struct timeval, con-
	      sisting of seconds and microseconds.

       timespec
	      A  double  float	specifying  seconds; the number is mapped into a struct timespec,
	      consisting of seconds and nanoseconds.

       UDP service
	      A service name, not starting with a digit, that is resolved by getservbyname() , or
	      an unsigned int 16 bit number read with strtoul() .

       unsigned int
	      A number read with strtoul() . The value must fit into a C unsigned int.

       user   If  the  first  character  is  a decimal digit, the value is read with strtoul() as
	      unsigned integer specifying a user id. Otherwise, it must be an existing user name.

EXAMPLES
       socat - TCP4:www.domain.org:80

	      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.

       socat -d -d READLINE,history=$HOME/.http_history \
       TCP4:www.domain.org:www,crnl

	      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;  socat  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.

       socat TCP4-LISTEN:www TCP4:www.domain.org:www

	      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 econd connection.

       socat -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

	      TCP port forwarder, each side bound to another local IP address (bind). This  exam-
	      ple  handles  an	almost arbitrary number of parallel or consecutive connections by
	      fork'ing a new process after each accept() .  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.

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

	      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 /home/sandbox, su's to user
	      sandbox, and then starts the program /home/sandbox/bin/myscript. Socat and myscript
	      communicate  via	a pseudo tty (pty); myscript's stderr is redirected to stdout, so
	      its error messages are transferred via socat to the connected client.

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

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

       socat -,raw,echo=0,escape=0x0f /dev/ttyS0,raw,echo=0,crnl

	      opens an interactive connection via the serial line, e.g. for talking with a modem.
	      raw  and echo set the console's and ttyS0's terminal parameters to practicable val-
	      ues, crnl converts to correct newline characters. escape allows  to  terminate  the
	      socat  process  with  character  control-O.  Consider using READLINE instead of the
	      first address.

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

	      with UNIX-LISTEN, socat opens a listening  UNIX  domain  socket  /tmp/.X11-unix/X1.
	      This  path  corresponds  to  local  XWindow  display :1 on your machine, so XWindow
	      client connections to DISPLAY=:1 are accepted. Socat then speaks	with  the  SOCKS4
	      server  host.victim.org that might permit sourceport 20 based connections due to an
	      FTP related weakness in its static IP filters. Socat  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  XWin-
	      dow  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.

       socat -u /tmp/readdata,seek-end=0,ignoreeof -

	      this is an example for unidirectional data transfer (-u). Socat transfers data from
	      file  /tmp/readdata  (implicit  address  GOPEN),	starting  at  its   current   end
	      (seek-end=0  lets socat 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).

       (sleep 5; echo PASSWORD; sleep 5; echo ls; sleep 1) |
       socat - EXEC:'ssh -l user server',pty,setsid,ctty

	      EXEC'utes an ssh session to server. Uses a pty for communication between socat  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 socat.

       socat -u TCP4-LISTEN:3334,reuseaddr,fork \
       OPEN:/tmp/in.log,creat,append

	      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.

       socat READLINE,noecho='[Pp]assword:' EXEC:'ftp ftp.server.com',pty,setsid,ctty

	      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.

	      (socat	 PTY,link=$HOME/dev/vmodem0,raw,echo=0,wait-slave    EXEC:'"ssh    modem-
	      server.us.org socat - /dev/ttyS0,nonblock,raw,echo=0"')

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

       socat TCP4-LISTEN:2022,reuseaddr,fork \
       PROXY:proxy:www.domain.org:22,proxyport=3128,proxyauth=user:pass

	      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  CON-
	      NECT  method,  where  they are authenticated as "user" with "pass" (proxyauth). The
	      proxy should establish connections to host www.domain.org on port 22 then.

       socat - SSL:server:4443,cafile=server.crt,cert=client.pem

	      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.
	      The first address ('-') can be replaced by almost any other socat address.

       socat SSL-LISTEN:4443,reuseaddr,pf=ip4,fork,cert=server.pem,cafile=client.crt PIPE

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

       echo |socat -u - file:/tmp/bigfile,create,largefile,seek=100000000000

	      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).

       socat tcp-l:7777,reuseaddr,fork system:'filan -i 0 -s >&2',nofork

	      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).

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

	      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).

       socat - tcp:www.blackhat.org:31337,readbytes=1000

	      connects to an unknown service and prevents being flooded.

       socat -U TCP:target:9999,end-close TCP-L:8888,reuseaddr,fork

	      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;  shut-
	      down\(2) would actively terminate the connection).

       socat - UDP4-DATAGRAM:192.168.1.0:123,sp=123,broadcast,range=192.168.1.0/24

	      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.

       socat					-				     SOCKET-DATA-
       GRAM:2:2:17:x007bxc0a80100x0000000000000000,bind=x007bx00000000x0000000000000000,setsock-
       opt-int=1:6:1,range=x0000xc0a80100x0000000000000000:x0000xffffff00x0000000000000000

	      is semantically equivalent to the previous example, but all parameters  are  speci-
	      fied  in	generic  form.	the  value  6  of  setsockopt-int  is the Linux value for
	      SO_BROADCAST.

       socat - IP4-DATAGRAM:255.255.255.255:44,broadcast,range=10.0.0.0/8

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

       socat - UDP4-DATAGRAM:224.255.0.1:6666,bind=:6666,ip-add-membership=224.255.0.1:eth0

	      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  pack-
	      ets  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 con-
	      figured switch.

       socat TCP:host2:4443 TUN:192.168.255.1/24,up

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

       socat PTY,link=/var/run/ppp,raw,echo=0 INTERFACE:hdlc0

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

       socat -T 1  -d  -d  TCP-L:10081,reuseaddr,fork,crlf  SYSTEM:"echo  -e  \"\\\"HTTP/1.0  200
       OK\\\nDocumentType:	 text/plain\\\n\\\ndate:       \$\(date\)\\\nserver:\$SOCAT_SOCK-
       ADDR:\$SOCAT_SOCKPORT\\\nclient: \$SOCAT_PEERADDR:\$SOCAT_PEERPORT\\\n\\\"\"; cat; echo -e
       \"\\\"\\\n\\\"\""

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

       socat	     -d 	 -d	     UDP4-RECVFROM:9999,so-broadcast,so-timestamp,ip-pkt-
       info,ip-recverr,ip-recvopts,ip-recvtos,ip-recvttl!!- SYSTEM:'export; sleep 1' |grep SOCAT

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

DIAGNOSTICS
       Socat  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)

       FATAL: Conditions that require unconditional and immediate program termination.

       ERROR: Conditions  that	prevent  proper program processing. Usually the program is termi-
	      nated (see option -s).

       WARNING:
	      Something did not function correctly or is in a state where  correct  further  pro-
	      cessing cannot be guaranteed, but might be possible.

       NOTICE:
	      Interesting  actions  of	the  program,  e.g. for supervising socat in some kind of
	      server mode.

       INFO:  Description of what the program does, and maybe why it happens. Allows  to  monitor
	      the lifecycles of file descriptors.

       DEBUG: Description  of  how  the  program  works,  all  system  or library calls and their
	      results.

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

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

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

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

       In the output variables beginning with "SOCAT" this prefix is  actually	replaced  by  the
       upper case name of the executable or the value of option -lp.

       SOCAT_DEFAULT_LISTEN_IP (input)
	      (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.

       SOCAT_PREFERRED_RESOLVE_IP (input)
	      (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.

       SOCAT_FORK_WAIT (input)
	      Specifies the time (seconds) to sleep the parent and child processes after success-
	      ful fork\(). Useful for debugging.

       SOCAT_VERSION (output)
	      Socat sets this variable to its version string, e.g. "1.7.0.0"  for  released  ver-
	      sions  or  e.g.  "1.6.0.1+envvar"  for  temporary  versions; can be used in scripts
	      invoked by socat.

       SOCAT_PID (output)
	      Socat sets this variable to its  process	id.  In  case  of  fork  address  option,
	      SOCAT_PID  gets the child processes id. Forking for exec and system does not change
	      SOCAT_PID.

       SOCAT_PPID (output)
	      Socat sets this variable to its process id. In case of fork, SOCAT_PPID  keeps  the
	      pid of the master process.

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

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

       SOCAT_SOCKADDR (output)
	      With all LISTEN addresses, this variable is set to a string  describing  the  local
	      socket address. Port information is not included example

       SOCAT_SOCKPORT (output)
	      With TCP-LISTEN, UDP-LISTEN, and SCTP-LISTEN addresses, this variable is set to the
	      local port.

       SOCAT_TIMESTAMP (output)
	      With all RECVFROM addresses where address option	so-timestamp  is  applied,  socat
	      sets this variable to the resulting timestamp.

       SOCAT_IP_OPTIONS (output)
	      With all IPv4 based RECVFROM addresses where address option ip-recvopts is applied,
	      socat fills this variable with the IP options of the received packet.

       SOCAT_IP_DSTADDR (output)
	      With all IPv4 based RECVFROM addresses where address option ip-recvdstaddr (BSD) or
	      ip-pktinfo  (other  platforms) is applied, socat sets this variable to the destina-
	      tion address of the received packet. This is particularly useful to identify broad-
	      cast and multicast addressed packets.

       SOCAT_IP_IF (output)
	      With  all  IPv4  based  RECVFROM	addresses where address option ip-recvif (BSD) or
	      ip-pktinfo (other platforms) is applied, socat sets this variable to  the  name  of
	      the interface where the packet was received.

       SOCAT_IP_LOCADDR (output)
	      With  all IPv4 based RECVFROM addresses where address option ip-pktinfo is applied,
	      socat sets this variable to the address of  the  interface  where  the  packet  was
	      received.

       SOCAT_IP_TOS (output)
	      With  all IPv4 based RECVFROM addresses where address option ip-recvtos is applied,
	      socat sets this variable to the TOS (type of service) of the received packet.

       SOCAT_IP_TTL (output)
	      With all IPv4 based RECVFROM addresses where address option ip-recvttl is  applied,
	      socat sets this variable to the TTL (time to live) of the received packet.

       SOCAT_IPV6_HOPLIMIT (output)
	      With  all  IPv6  based RECVFROM addresses where address option ipv6-recvhoplimit is
	      applied, socat sets this variable to the hoplimit value of the received packet.

       SOCAT_IPV6_DSTADDR (output)
	      With all IPv6 based RECVFROM addresses where  address  option  ipv6-recvpktinfo  is
	      applied,	socat  sets  this  variable  to  the  destination address of the received
	      packet.

       SOCAT_IPV6_TCLASS (output)
	      With all IPv6 based RECVFROM addresses  where  address  option  ipv6-recvtclass  is
	      applied, socat sets this variable to the transfer class of the received packet.

       HOSTNAME (input)
	      Is used to determine the hostname for logging (see -lh).

       LOGNAME (input)
	      Is used as name for the socks client user name if no socksuser is given.
	      With options su and su-d, LOGNAME is set to the given user name.

       USER (input)
	      Is used as name for the socks client user name if no socksuser is given and LOGNAME
	      is empty.
	      With options su and su-d, USER is set to the given user name.

       SHELL (output)
	      With options su and su-d, SHELL is set to the login shell of the given user.

       PATH (output)
	      Can be set with option path for exec and system addresses.

       HOME (output)
	      With options su and su-d, HOME is set to the home directory of the given user.

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

       The FSF (GNU, http://www.fsf.org/ project with their free and portable  development  soft-
       ware and lots of other useful tools and libraries.

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

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

VERSION
       This man page describes version 1.7.2 of socat.

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

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

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

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

       Send bug reports to <socat@dest-unreach.org>

SEE ALSO
       nc\(1),	netcat6\(1),  sock\(1),  rinetd\(8), cage\(1), socks.conf\(5), openssl\(1), stun-
       nel\(8), pty\(1), rlwrap\(1), setsid\(1)

       Socat home page http://www.dest-unreach.org/socat/

AUTHOR
       Gerhard Rieger <rieger@dest-unreach.org>

					     Dec 2011					 socat(1)


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