Tx11ssh provides a way to (forward or reverse) tunnel X11 traffic over ssh connection.
Read the manual page below file list for more information.
(Decide yourself which direction you consider being "reverse" and which "forward" tunneling ;)
The source code and documentation of newer versions of tx11ssh
is also available at
TX11SSH(1) User Commands TX11SSH(1) NAME tx11ssh - tunnel X11 traffic over ssh connection SYNOPSIS tx11ssh + [:[nums][:numd]] [--ssh-command command] [--ll num] args... tx11ssh - [:[nums][:numd]] [--ssh-command command] [--ll num] args... DESCRIPTION tx11ssh provides a way to tunnel X11 traffic over ssh connection, in either direction from initiator's point of view: + after connection is made, open windows from local clients to remote display - after connection is made, open windows from remote clients to local display The '+' option is convenient when ssh connection cannot be made in the direction for standard X11 forwarding provided by ssh(1) and the '-' is useful when sshd(8) is not configured to support X11 forwarding. Both systems at the tunnel endpoints need to have tx11ssh installed and available in PATH for normal usage. OPTIONS [:[nums][:numd]] Use these numbers in unix sockets created. The first number nums is the server socket to be created (i.e. /tmp/.X11-unix/Xnums) and the second numd display server socket where co connect. Default values are 11 and 0, respectively. Either can be omitted; e.g. :12 and ::1 are accepted. Under Linux if nums or numd is prefixed with @ the filesystem inde- pendent abstract namespace is used when creating these sockets. (Note that abstract namespace is in network namespace securitywise. For example LXC containers sharing network namespaces shares also this filesystem-independent abstract namespace of unix domain sock- ets.) --ssh-command command Execute command instead of 'ssh' for tunnel creation --ll num The "loglevel" of tx11ssh. With value 0 only severe warnings are printed to stderr. With value 4 all messages are printed. Default value is 2. args... "command line arguments" given to ssh when executed. Given verba- tim. This is flexible; tx11ssh can be executed with alternate path or wrappers can be used if needed, but this can also be used to break things (e.g. wrong paths or -f/n flags given to ssh...). SECURITY The normal X security concerns apply here, e.g. xinput(1) can be used to sneak X events of other windows. There is uid check for the X client connecting to the X unix domain socket done; whether this is enough one have to judge itself. Use of wrapx11usock.so shown below will at least hide the X socket from other users (security by obscurity when thinking about root users). EXAMPLES Case 1: One wants to open windows from Windows machine on a Unix desk- top; but configuring sshd to work on windows (cygwin) environment is nontrivial thing to do. From one Cygwin Terminal open x11ssh tunnel to unix host and from another execute urxvt terminal using display 11 (which is tx11ssh default) to open the urxvt terminal window to remote X display. cygwin-term1$ tx11ssh + user@unixhost cygwin-term2$ DISPLAY=:11 urxvt -fade 1 -tn rxvt-unicode & Case 2: Remote sshd is not configured to support X11 forwarding, there- fore it has to be done by "ourselves". The '-' option of tx11ssh makes the X11 unix domain server socket available on a remote host; the com- mand line on second terminal below uses the display 11 (tx11ssh default) to open the window of remote command on local X display. term1$ tx11ssh - user@host term2$ ssh -f user@host env DISPLAY=:11 urxvt Case 3: This is like case 2, but instead of using /tmp/.X11-unix/X11 for the X11 display unix domain socket, use $HOME/.ssh/X11 instead. The wrapx11usock preload library does the path mangling to achieve this. The reasons one might need this includes: security, multiuser support and filesystem permissions. The wrapx11usock.sh script (and the source for the preload library it uses) can be found in the source archive of tx11ssh. term1$ tx11ssh - user@host ./wrapx11usock.sh term2$ ssh -f user@host ./wrapx11usock.sh urxvt Case 4: Tunneling through a proxy. In some cases there the destination machine is not directly reachable; there is a "proxy" machine in between. Here are examples of ways how to handle the following two cases: There is ssh server to be connected first (2 examples below) or there is http CONNECT proxy to be used, respectively. term$ tx11ssh - -oProxyCommand='ssh user@proxy -W %h:%p' user@host term$ tx11ssh - -oProxyCommand='ssh user@proxy nc %h %p' user@host term$ tx11ssh - -oProxyCommand='corkscrew https_proxy 8080 %h %p' user@host The client execution (and all of the wrapping options) are the same. (Instead of '-W' the 'nc' alternative provides option to add more for- wardings to the proxy command (e.g. -D port); With '-W' all other for- warding attempts are cleared out.) DETACHING tx11ssh Perfect "detaching" from shell is impossible to implement in tx11ssh since one needs to detach from control terminal too. If detaching is postponed after ssh tunnel is created, the ssh process cannot be detached (anymore). If detach is done before executing ssh, interactive authentication methods on terminal cannot be done anymore. Therefore detaching, whenever anyone wants to do so, can be done at least with the the help of following commands(*): Non-interactive: nohup setsid tx11ssh + remote > tx11ssh.log nohup script -a -f -c 'tx11ssh + remote' tx11ssh.log >/dev/null dtach -n tx11ssh-dtach-s sh -n 'exec tx11ssh + remote 2>tx11ssh.log' Interactive, until detached: dtach -c tx11ssh-dtach-s sh -c 'exec tx11ssh + remote 2>tx11ssh.log' dtach -c tx11ssh-dtach-s script -c 'tx11ssh + remote' tx11ssh.log screen tx11ssh + remote tmux tx11ssh + remote (*) Interestingly at least in linux, both setsid(1) & script(1) escapes from terminal when execve'd from nohup(1) -- at least when executed from interactive shell running on a tty. AUTHOR Written by Tomi Ollila. LICENSE This software is licensed under 2-clause (Simplified) BSD License. SEE ALSO ssh(1), Xserver(1), X(7) tx11ssh 1.2 2014-02-08 TX11SSH(1)