socat

socat(1)                                                              socat(1)



NAME
       socat - Multipurpose relay (SOcket CAT)

SYNOPSIS
       socat [options] <address> <address>
       socat -V
       socat -?[?]
       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.  It might be one of the tools that one `has already
       needed´.

       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.

       Procan is a utility that prints information about process related
       system 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 lifecycle 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, 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 file
       descriptors via select(), and, when data is available, reads it in
       portions of at most 8192 bytes (change with option -b), performs
       newline character conversions if required, and writes the data to the
       other stream.

       When one of the streams effectively reaches EOF, the closing phase
       begins. Socat tries to transfer the EOF condition to the other stream,
       giving it a chance to terminate gracefully.

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.

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

       -??    Like -?, plus a list of all available address options. Some
              options are platform dependent, so this output is helpful for
              checking the particular implementation.

       -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).

       -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".

       -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 even if some security option could not
              be applied. With this option, socat is sloppy with errors and
              tries to continue (but still exits on fatals).

       -t<timeout>
              If 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.

       -u     Uses unidirectional mode. The first address is only used for
              reading, and the second address is only used for writing.

       -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 option group
              membership.

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 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 addresses; if a ´/´ is found before the first ´:´
       or ´,´, GOPEN is assumed.

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

       Zero or more address options may be given with each address. Options
       are members of option groups. With each address type there is a set of
       option groups defined. Only options belonging to one of these address
       groups may be used (except with option -g).  Options consist of an
       option keyword or an option keyword and a value, separated by ´=´.
       Option keywords are case insensitive.

       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 is used, an
       address might be used only for reading or for writing. Considering this
       is important with some address types.

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.
              <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>
              Invokes the program with execvp().  <command-line> is a simple
              command with arguments separated by single spaces. If the
              program name contains a ´/´, the part behind 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.
              Option groups: FD,FIFO,SOCKET,EXEC,FORK,TERMIOS,UNIX
              Useful options: path, fdin, fdout, chroot, su, su-d, pty,
              stderr, ctty, setsid, pipes, login
              See also: SYSTEM

       FD:<fdnum>
              Uses the file descriptor <fdnum>. It must already exist as valid
              UN*X file descriptor.
              Option groups: FD (FIFO,TERMIOS,BLK,REG,SOCKET,UNIX)
              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.
              Option groups: FD,REG,SOCKET,NAMED,OPEN,UNIX
              See also: OPEN, CREATE, UNIX-CONNECT

       IP4:<host>:<protocol>
              Opens a raw IPv4 socket with <protocol>, sends packets to <host>
              [IPv4 address] and receives packets from host.  Protocol 255
              uses the raw socket with the IP header being part of the data.
              Option groups: FD,SOCKET,IP4
              Useful options: ttl, broadcast
              See also: IP6, UDP4, UDP4-LISTEN

       IP6:<host>:<protocol>
              Opens a raw IPv6 socket with <protocol>, sends packets to <host>
              [IPv6 address] and receives packets from host.
              Option groups: FD,SOCKET,IP6
              Useful options: ttl, broadcast
              See also: IP4, UDP6, UDP6-LISTEN

       OPEN:<filename>
              Opens <filename> using the open() system call.  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, nofollow, append, rdonly, wronly,
              lock, ignoreeof
              See also: CREATE, GOPEN, UNIX-CONNECT

       OPENSSL:<host>:<port>
              Tries to establish a SSL connection to <port> [TCP service] on
              <host> [IPv4 address] using TCP/IPv4.
              Note: this is currently only an experimental integration of
              openssl!  (it does not provide any trust between the peers
              because is does not check certificates!)  Option groups:
              FD,SOCKET,SOCK_IP,IP_TCP,OPENSSL
              Useful options: ciphers, method, verify
              See also: TCP4

       PIPE:<filename>
              If <filename> already exists, it is opened.  If is does not
              exist, a named pipe is created and opened.
              Note: When a pipe is used for both reading and writing, it works
              as echo service.
              Option groups: FD,FIFO,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.
              Option groups: FD,FIFO
              See also: named pipe

       PROXY:<proxy>:<hostname>:<port>
              Connects to an HTTP proxy server on port 8080 using TCP/IPv4,
              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,TCP,HTTP
              Useful options: proxyport, ignorecr, proxyauth, crnl, bind, mss,
              sourceport
              See also: SOCKS, TCP4

       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.
              Option groups: FD,NAMED,PTY,TERMIOS
              Useful options: link, openpty, 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. 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
              See also: STDIO

       SOCKS4:<socks-server>:<host>:<port>
              Connects via <socks-server> [IPv4 address] to <host> [IPv4
              address] on <port> [TCP service], using socks version 4
              protocol.
              Option groups: FD,SOCKET,IP4,TCP,SOCKS4
              Useful options: socksuser, socksport, sourceport
              See also: SOCKS4A, TCP4

       SOCKS4A:<socks-server>:<host>:<port>
              Connects via <socks-server> [IPv4 address] to <host> [IPv4
              address] on <port> [TCP service].  This address uses version 4a
              of the socks protocol, thus it sends the destination host name
              unresolved in the socks request.
              Option groups: FD,SOCKET,IP4,TCP,SOCKS4
              Useful options: socksuser, socksport, sourceport
              See also: SOCKS4, TCP4

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

       STDIN  Uses file descriptor 0.
              Option groups: FD (FIFO,TERMIOS,BLK,REG,SOCKET,UNIX)
              See also: FD

       STDIO  Uses file descriptor 0 for reading, and 1 for writing.
              Option groups: FD (FIFO,TERMIOS,BLK,REG,SOCKET,UNIX)
              See also: FD

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

       SYSTEM:<shell-command>
              Invokes the 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,FIFO,SOCKET,EXEC,FORK,TERMIOS,UNIX
              Useful options: path, fdin, fdout, chroot, su, su-d, pty,
              stderr, ctty, setsid, pipes
              See also: EXEC

       TCP4:<host>:<port>
              Connects to <port> [TCP service] on <host> [IPv4 address] using
              TCP/IPv4.
              Option groups: FD,SOCKET,IP4,TCP
              Useful options: crnl, bind, tos, mtudiscover, mss, nodelay,
              nonblock, sourceport
              See also: TCP4-LISTEN, UDP4, TCP6, UNIX-CONNECT

       TCP4-LISTEN:<port>
              Listens on <port> [TCP service] and accepts a TCP/IPv4
              connection. Note that opening this address usually blocks until
              a client connects.
              Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,TCP
              Useful options: crnl, fork, bind, range, backlog, mss, su,
              reuseaddr
              See also: TCP4, UDP4-LISTEN, TCP6-LISTEN, UNIX-LISTEN

       TCP6:<host>:<port>
              Connects to <port> [TCP service] on <host> [IPv6 address] using
              TCP/IPv6.
              Option groups: FD,SOCKET,IP6,TCP
              Useful options: crnl, bind, tos, nodelay, nonblock
              See also: TCP6-LISTEN, UDP6, TCP4

       TCP6-LISTEN:<port>
              Listens on <port> TCP service] and accepts a TCP/IPv6
              connection. Note that opening this address usually blocks until
              a client connects.
              Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP6,TCP
              Useful options: crnl, fork, bind, range, backlog, reuseaddr
              See also: TCP6, UDP6-LISTEN, TCP4-LISTEN

       UDP4:<host>:<port>
              Connects to <port> [UDP service] on <host> [IPv4 address] using
              UDP/IPv4.  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,UDP
              Useful options: ttl, tos, bind, sourceport
              See also: UDP4-LISTEN, TCP4, UDP6

       UDP4-LISTEN:<port>
              Waits for a UDP/IPv4 packet arriving on <port> [UDP service] and
              `connects´ back to sender.  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,UDP
              Useful options: fork, bind, range
              See also: UDP4, TCP4-LISTEN, UDP6-LISTEN

       UDP6:<host>:<port>
              Connects to <port> [UDP service] on <host> [IPv6 address] using
              UDP/IPv6. 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,IP6,UDP
              Useful options: ttl, tos
              bind, sourceport, See also: UDP6-LISTEN, TCP6, UDP4

       UDP6-LISTEN:<port>
              Waits for a UDP/IPv6 packet arriving on <port> [UDP service] and
              `connects´ back to sender.  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,IP6,UDP
              Useful options: fork, bind, range
              See also: UDP6, TCP6-LISTEN, UDP4-LISTEN

       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,UNIX
              See also: UNIX-LISTEN, TCP4

       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.
              Option groups: FD,SOCKET,NAMED,LISTEN,CHILD,UNIX
              Useful options: fork, umask, mode, user, group, unlink-early
              See also: UNIX-CONNECT, TCP4-LISTEN

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 invokations. 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 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 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.

       setlkw Tries to set a discretionary waiting lock to the whole file
              using the fcntl(fd, F_SETLKW, ...) system call. If the file is
              already locked, this call blocks.

       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) 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 selected.

       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.  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.

       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.

       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.

       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.

       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) system call, thus
              positioning the file pointer absolutely to <offset> [long].

       seek-cur=<offset>
              Applies the lseek(fd, <offset>, SEEK_CUR) system call, thus
              positioning the file pointer <offset> [long] bytes relatively to
              its current position (which is usually 0).

       seek-end=<offset>
              Applies the lseek(fd, <offset>, SEEK_END) system call, thus
              positioning the file pointer <offset> [long] bytes relatively to
              the files current end.

       ftruncate=<offset>
              Applies the ftruncate(fd, <offset>) system call, thus truncating
              the file at the position <offset> [long].

       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 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. 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.

       setgid-early=<group>
              Changes the primary <group> of the process before opening the
              address. This call might require root privilege.

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

       setuid-early=<user>
              Changes the <user> (owner) of the process before opening the
              address. This call might require root privilege.

       su=<user>
              Changes the <user> (owner) and groups of the process after
              processing the address. 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.  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.

       READLINE option group

       These options apply to the readline address type.

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

       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. Note: with socat version 1.3.0.1, the semantics of this
              option have been changed for the input stream to simply strip
              all CR characters.

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

       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)], UNIX domain sockets
              require <filename>.

       interface=<interface>
              Binds the socket to the given <interface>.  With Linux, this is
              a string like "eth0".  This option might require root privilege.

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

       bsdcompat
              Emulates some (old?) bugs of the BSD socket implementation.

       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 correspondends 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
              correspondends with 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.

       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].

       type=<type>
              Sets the type of the socket, usually as argument to the socket()
              or socketpair() call, to <type> [int].  Under Linux, 1 means
              stream oriented socket, 2 means datagram socket, and 3 means raw
              socket.

       IP option group

       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].

       ipoptions=<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
              ipoptions=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.

       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 intervall 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.

       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).

       stdurg Enables RFC1122 compliant urgent pointer handling.

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

       UDP and TCP option groups

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

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

       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).

       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.

       RANGE option group

       The range option can be applied to listening network sockets.

       range=<address-range>
              After accepting a connection, tests if the peer is within range.
              This option is currently only implemented for IPv4 addresses.
              Address range has the form ww.xx.yy.zz/bits, e.g. 10.0.0.0/8. If
              the client address does not match, socat issues an error
              aborting the program or keeps listening (see option -s).

       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 listen addresses with child processes.

       fork   After accepting a connection, handles its channel in a child
              process and keeps the parent process listening.

       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.

       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/pts 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.

       ctty   Makes the pty the controlling tty of the sub process.

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

       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.

       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.

       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.

       Only a subset of the termios options is listed here; see the file
       xio.help of the socat documentation, or "man termios" for a
       comprehensive description.

       echo=<bool>
              Enables or disables local echo.

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

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

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

       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.

       cs5
       cs6
       cs7
       cs8

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

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

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

       nl0    Sets the newline delay to 0.

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

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

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

       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.

       OPENSSL option group

       These options apply to the openssl address type.

       ciphers=<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>
              Forces check of the peer´s certificate. Currently there is not
              certificate check implemented, therefore applying this option
              lets the connection fails.

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. 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. The only
              documented form is a string starting with ´x´ followed by an
              even number of hex digits.

       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.

       IPv4 address
              A hostname that is resolved by gethostbyname(), or an address in
              numbers-and-dots notation.
              Examples: www.dest-unreach.org, dns1, 127.0.0.1

       IPv6 address
              A hostname that is resolved by gethostbyname(), or an address in
              hexnumbers-and-colons notation.
              Examples: ip6name.domain.org, ::1,
              1234:5678:9abc:def0:1234:5678:9abc:def0

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

       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 byte2_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 int 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.

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

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

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

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

              Transfers data between STDIO (-) and a TCP4 connection to port
              80 of host www.domain.org. This example results in an
              interactive connection similar to telnet or netcat. The stdin
              terminal parameters are not changed, so you may close the relay
              with ^D or abort it with ^C.

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

              This is similar to the previous example, but you can edit the
              current line in a bash like manner (READLINE) and use the
              history file .http_history; socat prints messages about progress
              (-d -d). The  port is specified by service name (www), and
              correct network line termination characters (crnl) instead of NL
              are used.

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

              Installs a simple TCP port forwarder. With TCP4-LISTEN it
              listens on local port "www" until a connection comes in, accepts
              it, then connects to the remote host (TCP4) and starts data
              transfer. It will not accept a second connection.

       socat -d -d -lmlocal2 \
       TCP4-LISTEN:80,bind=myaddr1,su=nobody,fork,range=10.0.0.0/8,reuseaddr \
       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 \
       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.  For EXEC´uting the program, it 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 - /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 ttyS0´s terminal
              parameters to practicable values, crnl converts to correct
              newline characters. Consider using READLINE instead of `-´.

       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 correspondents with 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).

       (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 EXEC:´ftp ftp.server.com´,pty

              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 read directly from the terminal and
              therefore not echoed. pty is required to have ftp issue a
              prompt.  Nevertheless, there may occur some confusion with the
              password and FTP prompts.



              On server with modem:

       socat TCP4-LISTEN:54321 /dev/ttyS0

              On client: mkdir $HOME/dev

       socat PTY,link=$HOME/dev/vmodem0 TCP4:modemserver.us.org:54321

              Installs a TCP4 service on a modemserver and generates a pseudo
              terminal device (PTY) on the client that can be reached under
              the symbolic link $HOME/dev/vmodem0. Now an application on the
              client that expects a serial line or modem can be configured to
              use $HOME/dev/vmodem0; its traffic will be directed to
              /dev/ttyS0 on the modem server.

       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 authenticate as "user" with "pass" (proxyauth). The proxy
              should establish connections to host www.domain.org on port 22
              then.

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 (on 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.

       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

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.

       Sourceforge (http://www.sourceforge.net/) for providing a compile farm
       with Solaris, FreeBSD, and MacOS X machines, making these ports
       possible.

       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 1.3.0 of socat.

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

       In address specifications, characters with special meaning (´:´, ´,´,
       ´!!´) cannot be escaped, so it is hardly possible to directly invoke a
       second socat instance from an exec type addresses.

       IPv6 address specification does not allow ´[´ and ´]´.

       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.

       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(1), pty(1)

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

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



socat                            November 2002                        socat(1)