filan(1)


NAME

   socat - Multipurpose relay (SOcket CAT)

SYNOPSIS

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

DESCRIPTION

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

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

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

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

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

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

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

   When  one  of  the  streams  effectively reaches EOF, the closing phase
   begins. Socat transfers the EOF condition to  the  other  stream,  i.e.
   tries  to  shutdown  only  its  write  stream,  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 rarly 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 to utilize 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 to set flags with the open() system call.
   E.g., option `creat' sets the O_CREAT flag.
   See also options append and nonblock.

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

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

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

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

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

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

   nofollow=<bool>
          Does not follow symbolic links.

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

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

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

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

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

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

   trunc  Truncates the file to size 0 during opening it.

   REG and BLK option group

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

   seek=<offset>
          Applies  the  lseek(fd, <offset>, SEEK_SET) (or lseek64 ) system
          call, thus 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.

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

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

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

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

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

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

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

   type=<type>
          Sets the type of the socket, specified as second argument to the
          socket()   or  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.

   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   detailled   error
          information.

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

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

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

   ip-recvdstaddr
          Sets the IP_RECVDSTADDR socket option.  This  enables  receiving
          and logging of 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
          OPENSSLSSL-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 choosen 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 to terminate 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 to filter messages by
   severity. The severities provided are more or less compatible to the
   appropriate syslog priority. With one or up to four occurrences of the
   -d command line option, the lowest priority of messages that are issued
   can be selected. Each message contains a single uppercase character
   specifying the messages severity (one of F, E, W, N, I, or D)

   FATAL: Conditions that require unconditional and immediate program
          termination.

   ERROR: Conditions that prevent proper program processing. Usually the
          program is 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 to monitor the lifecycles of file descriptors.

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

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

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

FILES

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

ENVIRONMENT VARIABLES

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

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

   SOCAT_DEFAULT_LISTEN_IP (input)
          (Values 4 or 6) Sets the IP version to be used for listen, recv,
          and recvfrom addresses if no pf (protocol-family) option is
          given. Is overridden by socat options -4 or -6.

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

   SOCAT_FORK_WAIT (input)
          Specifies the time (seconds) to sleep the parent and child
          processes after 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), netcat6(1), sock(1), rinetd(8), cage(1), socks.conf(5),
   openssl(1), stunnel(8), pty(1), rlwrap(1), setsid(1)

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

AUTHOR

   Gerhard Rieger <rieger@dest-unreach.org>

                                                                  socat(1)





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