Provided by: socat_1.7.3.2-2ubuntu3_amd64 bug

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,
       giving it a chance to terminate gracefully. For a defined time socat continues to transfer
       data in the other direction, but then closes all remaining channels and terminates.

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
       specifications.

       -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
              particular 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".
              Third party libraries might not obey this option.

       -lf<logfile>
              Writes messages to  <logfile>  [filename]  instead  of  stderr.  Some  third  party
              libraries, in particular libwrap, might not obey this option.

       -ls    Writes  messages  to stderr (this is the default). Some third party libraries might
              not obey this option, in particular libwrap appears to only log to syslog.

       -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
              directions. 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
              transfer EOF.

       -u     Uses unidirectional mode. The first address is  only  used  for  reading,  and  the
              second 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,
              creates 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
       necessary information for establishing the byte streams.

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

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

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

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

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

       Usually, addresses are opened in read/write mode. When  an  address  is  part  of  a  dual
       address  specification, or when 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
       characters ( { [ ’ is found, the corresponding closing character - ) } ]  ’  -  is  looked
       for;  they  may  also  be  nested.  Within these constructs, socats special characters and
       strings : , !! are not handled specially. All those characters and strings can be  escaped
       with \ or within ""

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
              successful  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
              descriptor.
              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
              communications.
              Option groups: FD, SOCKET, IP4, IP6, RANGE
              Useful    options:    bind,    range,    tcpwrap,   broadcast,   ip-multicast-loop,
              ip-multicast-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
              broadcasts.
              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
              distinguish the sockets.
              This address works well with IP-SENDTO address peers  (see  above).   Protocol  255
              uses the raw socket with the IP header being part of the data.
              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 rarely useful in bidirectional mode.
              Option groups: FD,REG,NAMED,OPEN
              Useful  options:  creat,  excl,  noatime,  nofollow,  append, rdonly, wronly, lock,
              readbytes, 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: Up to version 1.7.2.4 the server certificate was only  checked  for  validity
              against  the  system  certificate store or cafile or capath, but not for match with
              the server’s name or its IP address.  Since version 1.7.3.0 socat checks  the  peer
              certificate   for   match   with   the   <host>  parameter  or  the  value  of  the
              openssl-commonname option.  Socat  tries  to  match  it  against  the  certificates
              subject  commonName,  and  the  certifications  extension subjectAltName DNS names.
              Wildcards in the certificate are supported.
              Option groups: FD,SOCKET,IP4,IP6,TCP,OPENSSL,RETRY
              Useful options: cipher, method, verify,  commonname  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, commonname cafile, capath, certificate,
              key, compress, 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
              depending  on  address  specification,  name  resolution, or option pf, and sends a
              CONNECT request for hostname:port. If the  proxy  grants  access  and  succeeds  to
              connect  to  the target, data transfer between socat and the target can start. Note
              that the traffic need not be HTTP but can be an arbitrary protocol.
              Option groups: FD,SOCKET,IP4,IP6,TCP,HTTP,RETRY
              Useful   options:   proxyport,   ignorecr,   proxyauth,   resolve,   crnl,    bind,
              connect-timeout, 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).
              Due to licensing restrictions the readline feature  is  disabled  in  Debian.   See
              BUGS.
              You can use STDIO instead.

       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
              specification, 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
              environment 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  documentation  and
              include  files  to find the appropriate values. The remote-address must be the data
              representation  of  a  sockaddr  structure  without  sa_family  and  (BSD)   sa_len
              components.
              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
              parameters have to be specified by int numbers. Consult your OS  documentation  and
              include  files  to find the appropriate values. The remote-address must be the data
              representation  of  a  sockaddr  structure  without  sa_family  and  (BSD)   sa_len
              components.
              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.
              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.
              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 parameters have
              to be specified as int numbers. Consult your OS documentation and include files  to
              find  the appropriate values. The remote-address must be the data representation of
              a sockaddr structure without sa_family and (BSD) sa_len components.
              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
              environment  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
              interface!
              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
              established; data has to be sent for `connecting’ to the server, and no end-of-file
              condition 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
              correct remote port and if their source addresses match RANGE or  TCPWRAP  options.
              This  address type can for example be used for implementing symmetric or asymmetric
              broadcast or multicast communications.
              Option groups: FD,SOCKET,IP4,IP6,RANGE
              Useful   options:   bind,    range,    tcpwrap,    broadcast,    ip-multicast-loop,
              ip-multicast-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
              specification, name resolution, or option pf. It  sends  packets  to  and  receives
              packets from that peer socket only.  This address effectively implements a datagram
              client.  It works well with socat UDP-RECVFROM and UDP-RECV address peers.
              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-LISTEN, 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-LISTEN, 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
              connects.  Beginning with socat version 1.4.3, the file  system  entry  is  removed
              when this address is closed (but see option unlink-close) (example).
              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 necessary 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
              member of the NAMED group.

ADDRESS OPTIONS

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

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

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

       FD option group

       This option group contains options that are applied to a UN*X style  file  descriptor,  no
       matter  how it was generated.  Because all current socat address types are file descriptor
       based, these options may be applied to any address.
       Note: Some of these options are  also  member  of  another  option  group,  that  provides
       another, non-fd based mechanism.  For these options, it depends on the actual address type
       and its option groups which mechanism is used.  The  second,  non-fd  based  mechanism  is
       prioritized.

       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
              connect()  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
              (Cygwin).

       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
              explicitly 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
              connection to not do anything.

       shut-down
              Changes the (address dependent) method  of  shutting  down  the  write  part  of  a
              connection 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
              connection 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
              datagram 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 utilizing ioctls that are not explicitly 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
              integer 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
              operations 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
              processes 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 setting 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 sharing 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
              positioning 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
              positioning  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
              positioning the file pointer <offset> [off_t or off64_t] bytes  relatively  to  the
              files current 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
              (example). 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

       Due to licensing restrictions the readline feature is disabled in Debian (see BUGS).
       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
              output.  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
              simply 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,
              creates 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
              [hostname|hostaddress][:(service|port)]  (example),  UNIX  domain  sockets  require
              <filename>.

       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
              privilege.

       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
              timeout [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.

       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].

       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
              socketpair()  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.

       reuseport
              Set the SO_REUSEPORT socket option.

       so-timestamp
              Sets  the  SO_TIMESTAMP  socket  option.  This  enables  receiving  and  logging of
              timestamp 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
              system.  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
              format is a leading "x" followed by an even number of hex digits. This  option  may
              be  used  multiple times, data are appended.  E.g., to connect to host 10.0.0.1 via
              some gateway using a loose source route, use the gateway as address  parameter  and
              set a loose source route using the option 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 detailed 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
              ancillary 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
              connections 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
              ancillary messages containing routing information.

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

       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.
              Nevertheless, 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
              hostname.  With  this  option, socat resolves the hostname locally and sends the IP
              address. Please note that, according to RFC 2396,  only  name  resolution  to  IPv4
              addresses is implemented.

       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).
              OPENSSL-CONNECT and OPENSSL-LISTEN differ in when they actually fork off the child:
              OPENSSL-LISTEN   forks  before  the  SSL  handshake,  while  OPENSSL-CONNECT  forks
              afterwards.  RETRY and FOREVER options are not inherited by the child process.
              On some operating systems (e.g. FreeBSD) this option does not work  for  UDP-LISTEN
              addresses.

       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
              restrictions:

       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
              something  like  socat  -hh  |grep  ’  b[1-9]’ to find all speeds supported by your
              implementation.
              Note: On some operating systems, these options may not be available. Use ispeed  or
              ospeed instead.

       echo=<bool>
              Enables or disables local echo.

       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. This option is
              obsolete, use option rawer or cfmakeraw instead.

       rawer  Makes terminal rawer than raw  option.  This  option  implicitly  turns  off  echo.
              (example).

       cfmakeraw
              Sets  raw  mode  by  invoking  cfmakeraw()  or by simulating this call. This option
              implicitly turns off echo.

       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
              supports      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
              unpredictable names, making it difficult to directly access the socat generated pty
              automatically. With this option, the user can specify a "fix"  point  in  the  file
              hierarchy  that helps him to access the actual pty (example).  Beginning with 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:

       SSL2   Select SSL protocol version 2.

       SSL3   Select SSL protocol version 3.

       SSL23  Select the best available SSL or TLS protocol. This is the default when this option
              is not provided.

       TLS1   Select TLS protocol version 1.

       TLS1.1 Select TLS protocol version 1.1.

       TLS1.2 Select TLS protocol version 1.2.

       DTLS1  Select DTLS 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
              gathering  daemon  can be utilized, this option activates a mechanism for providing
              pseudo entropy. This is archieved by taking the current time  in  microseconds  for
              feeding  the  libc pseudo random number generator with an initial value. openssl is
              then feeded with output from random() calls.
              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
              compression-related settings.  NOTE: Requires OpenSSL 0.9.8 or higher and disabling
              compression with OpenSSL 0.9.8 affects all new connections in the process.

       commonname=<string>
              Specify the commonname that the peer certificate must match.  With  OPENSSL-CONNECT
              address this overrides the given hostname or IP target address; with OPENSSL-LISTEN
              this turns on check of peer certificates commonname. This option has  only  meaning
              when  option  verify  is  not  disabled  and  the  chosen  cipher  provides  a peer
              certificate.

       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
              generated (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
              hostname 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
              strtoul() .

       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,
              consisting 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 second 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
              example  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 -,escape=0x0f /dev/ttyS0,rawer,crnl

              opens an interactive connection via the serial line, e.g. for talking with a modem.
              rawer  sets  the  console’s  and ttyS0’s terminal parameters to practicable values,
              crnl converts to correct newline characters. escape allows  terminating  the  socat
              process with character control-O.

       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
              XWindow server and, if it does not require MIT cookies or Kerberos  authentication,
              we  can  start  work.  Please note that there can only be one connection at a time,
              because TCP can establish only one session with a given set of addresses and ports.

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

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

       socat - OPENSSL: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 OPENSSL-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 -en "\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;
              shutdown(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-DATAGRAM:2:2:17:x007bxc0a80100x0000000000000000,b‐
       ind=x007bx00000000x0000000000000000,setsockopt-int=1:6:1,r‐
       ange=x0000xc0a80100x0000000000000000:x0000xffffff00x0000000000000000

              is semantically equivalent to the previous example, but all parameters are
              specified 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
              packets of the given group. Multiple hosts on the local network can run this
              command, so all data sent by any of the hosts will be received by all the other
              ones. Note that there are many possible reasons for failure, including IP-filters,
              routing issues, wrong interface selection by the operating system, bridges, or a
              badly configured switch.

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

       FATAL: Conditions that require unconditional and immediate program termination.

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

       WARNING:
              Something did not function correctly or is in a state where correct further
              processing 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 monitoring
              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
              successful fork(). Useful for debugging.

       SOCAT_VERSION (output)
              Socat sets this variable to its version string, e.g. "1.7.0.0" for released
              versions 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
              destination address of the received packet. This is particularly useful to identify
              broadcast 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.

       SOCAT_OPENSSL_X509_ISSUER (output)
              Issuer field from peer certificate

       SOCAT_OPENSSL_X509_SUBJECT (output)
              Subject field from peer certificate

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

       SOCAT_OPENSSL_X509_* (output)
              all other entries from peer certificates subject

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

       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
       software 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 1.7.3 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
       direction.

       The licenses of OpenSSL and GNU Readline are incompatible. Therefore readline support is
       disabled in Debian.

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

SEE ALSO

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

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

AUTHOR

       Gerhard Rieger <rieger@dest-unreach.org>

                                                                                         socat(1)