SSH Options: Control Socket, Subsystem, TTY, Version, Verbose, Forwarding, Tunneling, and X11

8th chunk of `ssh.man`

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 the allocated port will be
               printed to the standard output.

       -S ctl_path
               Specifies the location of a control socket for connection  shar‐
               ing,  or the string “none” to disable connection sharing.  Refer
               to  the  description  of  ControlPath   and   ControlMaster   in
               ssh_config(5) for details.

       -s      May  be  used to request invocation of a subsystem on the remote
               system.  Subsystems facilitate the use of SSH as a secure trans‐
               port for other applications (e.g. sftp(1)).   The  subsystem  is
               specified  as  the  remote command.  Refer to the description of
               SessionType in ssh_config(5) for details.

       -T      Disable pseudo‐terminal allocation.

       -t      Force pseudo‐terminal allocation.  This can be used  to  execute
               arbitrary  screen‐based  programs on a remote machine, which can
               be very useful, e.g. when implementing menu services.   Multiple
               -t options force tty allocation, even if ssh has no local tty.

       -V      Display the version number and exit.

       -v      Verbose  mode.  Causes ssh to print debugging messages about its
               progress.  This is helpful in debugging connection,  authentica‐
               tion,  and configuration problems.  Multiple -v options increase
               the verbosity.  The maximum is 3.

       -W host:port
               Requests that standard input and output on the  client  be  for‐
               warded to host on port over the secure channel.  Implies -N, -T,
               ExitOnForwardFailure  and  ClearAllForwardings, though these can
               be overridden in the configuration file or using -o command line
               options.

       -w local_tun[:remote_tun]
               Requests tunnel device forwarding with the specified tun(4)  de‐
               vices   between   the   client   (local_tun)   and   the  server
               (remote_tun).

               The devices may be specified by  numerical  ID  or  the  keyword
               “any”,   which  uses  the  next  available  tunnel  device.   If
               remote_tun is not specified, it defaults to “any”.  See also the
               Tunnel and TunnelDevice directives in ssh_config(5).

               If the Tunnel directive is unset, it will be set to the  default
               tunnel  mode,  which is “point‐to‐point”.  If a different Tunnel
               forwarding mode it desired, then it should be  specified  before
               -w.

       -X      Enables  X11  forwarding.   This can also be specified on a per‐
               host basis in a configuration file.

               X11 forwarding should be enabled with caution.  Users  with  the
               ability  to  bypass file permissions on the remote host (for the
               user’s X authorization database) can access the local  X11  dis‐
               play  through the forwarded connection.  An attacker may then be
               able to perform activities such as keystroke monitoring.

               For this reason, X11 forwarding is subjected to X11 SECURITY ex‐
               tension restrictions by default.  Refer to the ssh -Y option and
               the ForwardX11Trusted directive in ssh_config(5) for more infor‐
               mation.

               (Debian‐specific: X11 forwarding is not subjected to  X11  SECU‐
               RITY  extension  restrictions  by default, because too many pro‐
               grams currently crash in this mode.  Set  the  ForwardX11Trusted
               option  to  “no”  to  restore  the upstream behaviour.  This may
               change in future depending on client‐side improvements.)

       -x      Disables X11 forwarding.

       -Y      Enables trusted X11 forwarding.  Trusted X11 forwardings are not
               subjected to the X11 SECURITY extension controls.

Title: SSH Options: Control Socket, Subsystem, TTY, Version, Verbose, Forwarding, Tunneling, and X11

Summary

This section details various SSH options including `-S` (control socket for connection sharing), `-s` (subsystem invocation), `-T` and `-t` (TTY allocation control), `-V` (display version), `-v` (verbose mode), `-W` (forwarding standard input/output), `-w` (tunnel device forwarding), `-X` (enable X11 forwarding), `-x` (disable X11 forwarding), and `-Y` (enable trusted X11 forwarding).