socat(1)                                                              socat(1)



NAME
       socat - Multipurpose relay (SOcket CAT)

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

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

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

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

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

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

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

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

       When one of the streams effectively reaches EOF, the closing phase
       begins. Socat transfers the EOF condition to the other stream, i.e.
       tries to shutdown only its write stream, 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".

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

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

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

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

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

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

       -v     Writes the transferred data not only to their target streams,
              but also to stderr. The output format is text with some
              conversions for readability, and prefixed with "> " or "< "
              indicating flow directions.

       -x     Writes the transferred data not only to their target streams,
              but also to stderr. The output format is hexadecimal, prefixed
              with "> " or "< " indicating flow 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.  <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 procotol version 4 or 6 is used. It uses <protocol> to
              send packets to <host> [IP address] and receives packets from
              host, ignores packets from other hosts.  Protocol 255 uses the
              raw socket with the IP header being part of the data.
              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
              procotol version 4 or 6 is used. It receives one packet from an
              unspecified peer and may send one or more answer packets to that
              peer.  This mode is particularly useful with fork option where
              each arriving packet - from arbitrary peers - is handled by its
              own sub process.  This allows a behaviour similar to typical UDP
              based servers like ntpd or named.
              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
              procotol version 4 or 6 is used. It receives packets from
              multiple unspecified peers and merges the data.  No replies are
              possible.  It can be, e.g., addressed by socat IP-SENDTO address
              peers.  Protocol 255 uses the raw socket with the IP header
              being part of the data.
              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: The server certificate is only checked for validity
              against cafile or capath, but not for match with the server's
              name or its IP address!
              Option groups: FD,SOCKET,IP4,IP6,TCP,OPENSSL,RETRY
              Useful options: cipher, method, verify, cafile, capath,
              certificate, key, bind, pf, connect-timeout, sourceport, retry
              See also: OPENSSL-LISTEN, TCP

       OPENSSL-LISTEN:<port>
              Listens on tcp <port> [TCP service].  The IP version is 4 or the
              one specified with pf. When a connection is accepted, this
              address behaves as SSL server.
              Note: You probably want to use the certificate option with this
              address.
              NOTE: The client certificate is only checked for validity
              against cafile or capath, but not for match with the client's
              name or its IP address!
              Option groups:
              FD,SOCKET,IP4,IP6,TCP,LISTEN,OPENSSL,CHILD,RANGE,RETRY
              Useful options: pf, cipher, method, verify, cafile, capath,
              certificate, key, fork, bind, range, tcpwrap, su, reuseaddr,
              retry
              See also: OPENSSL, TCP

       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). This requires the GNU readline
              and history libraries. Note that stdio should be a (pseudo)
              terminal device, otherwise readline does not seem to work.
              Option groups: FD,READLINE,TERMIOS
              Useful options: history, noecho
              See also: STDIO

       SCTP-CONNECT:<host>:<port>
              Establishes an SCTP stream connection to the specified <host>
              [IP address] and <port> [TCP service] using TCP/IP version 4 or
              6 depending on address 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, 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, 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 assignes to it the address
              and netmask defined by the parameters. The resulting network
              interface is ready for use by other processes; socat serves its
              "wire side". This address requires read and write access to the
              tunnel cloning device, usually /dev/net/tun .
              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 neccessary to bind the local
              socket to an address (e.g. /tmp/sock1, which must not exist
              before).  This address type works well with socat UNIX-RECVFROM
              and UNIX-RECV address peers.
              Option groups: FD,SOCKET,NAMED,UNIX
              Useful options: bind
              See also: UNIX-RECVFROM, UNIX-RECV, UNIX-CONNECT, UDP-SENDTO,
              IP-SENDTO

       UNIX-RECVFROM:<filename>
              Creates a UNIX domain datagram socket [<filename>].  Receives
              one packet and may send one or more answer packets to that peer.
              This mode is particularly useful with fork option where each
              arriving packet - from arbitrary peers - is handled by its own
              sub process.  This address works well with socat UNIX-SENDTO
              address peers.
              Option groups: FD,SOCKET,NAMED,CHILD,UNIX
              Useful options: fork
              See also: UNIX-SENDTO, UNIX-RECV, UNIX-LISTEN, UDP-RECVFROM, IP-
              RECVFROM

       UNIX-RECV:<filename>
              Creates a UNIX domain datagram socket [<filename>].  Receives
              packets from multiple unspecified peers and merges the data.  No
              replies are possible. It can be, e.g., addressed by socat UNIX-
              SENDTO address peers.  It behaves similar to a syslog server.
              Option groups: FD,SOCKET,NAMED,UNIX
              See also: UNIX-SENDTO, UNIX-RECVFROM, UNIX-LISTEN, UDP-RECV, IP-
              RECV

       UNIX-CLIENT:<filename>
              Communicates with the specified peer socket, defined by
              [<filename>] assuming it is a UNIX domain socket.  It first
              tries to connect and, if that fails, assumes it is a datagram
              socket, thus supporting both types.
              Option groups: FD,SOCKET,NAMED,UNIX
              Useful options: bind
              See also: UNIX-CONNECT, UNIX-SENDTO, GOPEN

       ABSTRACT-CONNECT:<string>

       ABSTRACT-LISTEN:<string>

       ABSTRACT-SENDTO:<string>

       ABSTRACT-RECVFROM:<string>

       ABSTRACT-RECV:<string>

       ABSTRACT-CLIENT:<string>
              The ABSTRACT addresses are almost identical to the related UNIX
              addresses except that they do not address file system based
              sockets but an alternate UNIX domain address space. To archieve
              this the socket address strings are prefixed with "\0"
              internally. This feature is available (only?) on Linux.  Option
              groups are the same as with the related UNIX addresses, except
              that the ABSTRACT addresses are not 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 an other, non-fd based mechanism.  For these options, it
       depends on the actual address type and its option groups which
       mechanism is used. The second, non-fd based mechanism is prioritized.

       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 explicitely kill the sub process. With this
              option, it will just close the file descriptors.

       shut-none
              Changes the (address dependent) method of shutting down the
              write part of a 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 explicitely implemented in socat.

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

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

       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.


       CHILD option group

       Options for addresses with multiple connections via child processes.

       fork   After establishing a connection, handles its channel in a child
              process and keeps the parent process attempting to produce more
              connections, either by listening or by connecting in a loop
              (example).
              SSL-CONNECT and SSL-LISTEN differ in when they actually fork off
              the child: SSL-LISTEN forks before the SSL handshake, while SSL-
              CONNECT forks afterwards.  RETRY and FOREVER options are not
              inherited by the child process.


       EXEC option group

       Options for addresses that invoke a program.

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

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


       FORK option group

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

       nofork Does not fork a subprocess for executing the program, instead
              calls execvp\() or system\() directly from the actual socat
              instance. This avoids the overhead of another process between
              the program and its peer, but introduces a lot of 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 (example).

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

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

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

       brkint=<bool>

       bs0

       bs1

       bsdly=<0|1>

       clocal=<bool>


       cr0
       cr1
       cr2
       cr3

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

       crdly=<0|1|2|3>

       cread=<bool>

       crtscts=<bool>


       cs5
       cs6
       cs7
       cs8

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

       csize=<0|1|2|3>

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

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

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

       echoe=<bool>

       echok=<bool>

       echoke=<bool>

       echonl=<bool>

       echoprt=<bool>

       eof=<byte>

       eol=<byte>

       eol2=<byte>

       erase=<byte>

       discard=<byte>

       ff0

       ff1

       ffdly=<bool>

       flusho=<bool>

       hupcl=<bool>

       icrnl=<bool>

       iexten=<bool>

       igncr=<bool>

       ignpar=<bool>

       imaxbel=<bool>

       inlcr=<bool>

       inpck=<bool>

       intr=<byte>

       isig=<bool>

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

       istrip=<bool>

       iuclc=<bool>

       ixany=<bool>

       ixoff=<bool>

       ixon=<bool>

       kill=<byte>

       lnext=<byte>

       min=<byte>

       nl0    Sets the newline delay to 0.

       nl1

       nldly=<bool>

       noflsh=<bool>

       ocrnl=<bool>

       ofdel=<bool>

       ofill=<bool>

       olcuc=<bool>

       onlcr=<bool>

       onlret=<bool>

       onocr=<bool>

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

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

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

       parmrk=<bool>

       parodd=<bool>

       pendin=<bool>

       quit=<byte>

       reprint=<byte>

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

       start=<byte>

       stop=<byte>

       susp=<byte>

       swtc=<byte>

       tab0

       tab1

       tab2

       tab3

       tabdly=<unsigned-int>

       time=<byte>

       tostop=<bool>

       vt0

       vt1

       vtdly=<bool>

       werase=<byte>

       xcase=<bool>

       xtabs

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

       i-push=<string>
              With UNIX System V STREAMS, pushes the driver (module) with the
              given name (string) onto the stack. For example, to make sure
              that a character device on Solaris 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:

       SSLv2  Select SSL protocol version 2.

       SSLv3  Select SSL protocol version 3.

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

       TLSv1  Select TLS protocol version 1.

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

       cert=<filename>
              Specifies the file with the certificate and private key for
              authentication.  The certificate must be in OpenSSL format
              (*.pem).  With openssl-listen, use of this option is strongly
              recommended. Except with cipher aNULL, "no shared ciphers" error
              will occur when no certificate is given.

       key=<filename>
              Specifies the file with the private key. The private key may be
              in this file or in the file given with the cert option. The
              party that has to proof that it is the owner of a certificate
              needs the private key.

       dhparams=<filename>
              Specifies the file with the Diffie Hellman parameters. These
              parameters may also be in the file given with the cert option in
              which case the dhparams option is not needed.

       cafile=<filename>
              Specifies the file with the trusted (root) authority
              certificates. The file must be in PEM format and should contain
              one or more certificates. The party that checks the
              authentication of its peer trusts only certificates that are in
              this file.

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

       egd=<filename>
              On some systems, openssl requires an explicit source of random
              data. Specify the socket name where an entropy gathering daemon
              like egd provides random data, e.g. /dev/egd-pool.

       pseudo On systems where openssl cannot find an entropy source and where
              no entropy 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!

       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 econd connection.

       socat -d -d -lmlocal2 \
       TCP4-LISTEN:80,bind=myaddr1,reuseaddr,fork,su=nobody,range=10.0.0.0/8 \
       TCP4:www.domain.org:80,bind=myaddr2

              TCP port forwarder, each side bound to another local IP address
              (bind). This 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 -,raw,echo=0,escape=0x0f /dev/ttyS0,raw,echo=0,crnl


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

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

              with UNIX-LISTEN, socat opens a listening UNIX domain socket
              /tmp/.X11-unix/X1. This path corresponds to local XWindow
              display :1 on your machine, so XWindow client connections to
              DISPLAY=:1 are accepted. Socat then speaks with the SOCKS4
              server host.victim.org that might permit sourceport 20 based
              connections due to an FTP related weakness in its static IP
              filters. Socat pretends to be invoked by socksuser nobody, and
              requests to be connected to loopback port 6000 (only weak sockd
              configurations will allow this). So we get a connection to the
              victims 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 READLINE,noecho='[Pp]assword:' EXEC:'ftp
       ftp.server.com',pty,setsid,ctty


              wraps a command line history (READLINE) around the EXEC'uted ftp
              client utility.  This allows editing and reuse of FTP commands
              for relatively comfortable browsing through the ftp directory
              hierarchy. The password is echoed!  pty is required to have ftp
              issue a prompt.  Nevertheless, there may occur some confusion
              with the password and FTP prompts.

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

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

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

              starts a forwarder that accepts connections on port 2022, and
              directs them through the proxy daemon listening on port 3128
              (proxyport) on host proxy, using the 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 - SSL:server:4443,cafile=server.crt,cert=client.pem


              is an OpenSSL client that tries to establish a secure connection
              to an SSL server. Option cafile specifies a file that contains
              trust certificates: we trust the server only when it presents
              one of these certificates and proofs that it owns the related
              private key.  Otherwise the connection is terminated.  With cert
              a file containing the client certificate and the associated
              private key is specified. This is required in case the server
              wishes a client authentication; many Internet servers do not.
              The first address ('-') can be replaced by almost any other
              socat address.

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


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

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


              creates a 100GB sparse file; this requires a file system type
              that supports this (ext2, ext3, reiserfs, jfs; not minix, vfat).
              The operation of writing 1 byte might take long (reiserfs: some
              minutes; ext2: "no" time), and the resulting file can consume
              some disk space with just its inodes (reiserfs: 2MB; ext2:
              16KB).

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


              listens for incoming TCP connections on port 7777. For each
              accepted connection, invokes a shell. This shell has its stdin
              and stdout directly connected to the TCP socket (nofork).  The
              shell starts filan and lets it print the socket addresses to
              stderr (your terminal window).

       echo -e


              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,bind=x007bx00000000x0000000000000000,setsockopt-
       int=1:6:1,range=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 TCP-L and tun
              address 192.168.255.2. They can reach each other using the
              addresses 192.168.255.1 and 192.168.255.2. Substitute the TCP
              link with an SSL connection protected by client and server
              authentication (see OpenSSL client and server).

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


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

       socat -T 1 -d -d TCP-L:10081,reuseaddr,fork,crlf SYSTEM:


              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/local/bin/socat
       /usr/local/bin/filan
       /usr/local/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.

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

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

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

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

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



                                   Jan 2010                           socat(1)
