Ssh – How to one send commands to the “inner” ssh session

ssh

Picture a scenario where I'm logged into a server (which we'll call "Wallace") from my local machine, and from there I ssh into another server (which we'll call "Gromit"):

laptop ---ssh---> Wallace ---ssh---> Gromit

Then the ssh session from Wallace to Gromit hangs, and I want to kill it. If I enter ~. to kill ssh, it kills the ssh session from my laptop to Wallace, because the ~ is intercepted by that ssh session, and the . is taken as a command to kill the session. How do I send a command to the ssh session between Wallace and Gromit? How do I kill my "inner" ssh?

Best Answer

Add another tilde (ie, type ~~.). Each successive tilde is eaten by the outermost ssh session which hasn't yet eaten one, but if the next character is another tilde, it's passed along to the next session in.

If, from gromit¹, you ssh'ed to a third host (let's call it wensleydale), then ~~~. would drop the session to wensleydale and return you to a prompt on gromit.

¹ And what a great server that is; how often have I heard a developer remark "cracking host, gromit"?

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From a workstation that is already running X11 you can ssh in with the -X option to enable X11 forwarding. Or set the ForwardX11 option to yes in your ssh configuration file. If you are connecting from windows you probably want Xming and to enable X11 forwarding in Putty. (see this)

With X11 forwarding enabled it will allow the remote X11 applications to connect to and use the X11 server on your workstation.

The server will need to allow X11 forwarding. See the sshd_config and set X11Forwarding to yes.

If everything worked correctly then once you have connected running the running the command on the remote echo $DISPLAY should display something like this.

# echo $DISPLAY
localhost:10.0

You can also test by running simple like xclock or xeyes. The application should be displayed on your workstation.

SSH – Launch a Screen Session with a Command Over SSH on a Remote Server

Try using the -t option to ssh

ssh -t root@my.machine screen "tail -f /var/log/messages"

From man ssh

-t      Force pseudo-tty allocation.  This can be used to execute arbi-
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Best Answer

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Linux SSH – How to Run Commands in Open X Session

SSH – Launch a Screen Session with a Command Over SSH on a Remote Server

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