detecting a shared ssh session

Question

In my job, I have to ssh to loads of different machines. To make my life easier, I have been trying to set the colorscheme of each machine automatically so that I can tell at a glance which one I happen to be working on.

It is almost working.

~/.ssh/config:

Host some-remote-server
    Hostname some-remote-server.ac.uk
    User myusername
    IdentityFile ~/.ssh/id_rsa
    ForwardAgent yes
    ForwardX11 yes

Host some-other-remote-server
    Hostname some-other-remote-server.ac.uk
    User myusername
    IdentityFile ~/.ssh/id_rsa
    ForwardAgent yes
    ForwardX11 yes
    ProxyCommand ssh -Y some-remote-server -W %h:%p
    ControlMaster auto
    ControlPath /tmp/ssh-socket-%r@%h-%p
    ControlPersist 600

Let's pretend I want both "some-remote-server" and "some-other-remote-server" to be blue and I want "my-local-server" to be red.

Logging in is no problem; there is some code in "~/.profile" which sets the colorscheme appropriately. However, logging out is problematic.

~/.bash_logout:

if [[ $- == *i* ]]; then
  ORIGIN_HOST=`who am i | awk -F"[()]" '{print $2}'`
  $HOME/bin/set_the_colorscheme $ORIGIN_HOST
fi

When I exit an ssh session from my-local-server to some-other-remote-server, the above script identifies $ORIGIN_HOST as "some-remote-server" (b/c of the ControlMaster setting in my SSH config file) and so the colors stay blue.

Is there anyway to detect that I am using ControlMaster and find the host that issued the original ssh command?

Thanks.

Answer 1

It sounds like your real goal is to restore the terminal settings after terminating an SSH session. Here is a solution that follows a slightly different path than the one you were on. This is based on solutions from other posts:

• How to automatically run a command after exiting ssh

• SSH LocalCommand on exit

• Fix terminal title after SSH remote logging to another machine

• “Reset” colors of terminal after ssh exit/logout

You can define a wrapper/shim function to execute some code after the SSH session terminates:

function ssh () { command ssh "$@"; echo "SSH session terminated!"; }

Using this wrapper you can reset your terminal environment based on the current host. In particular, you could do something like the following:

$ mkdir -p ~/.ssh/exit_scripts

$ cat <<HEREDOC > "${HOME}/.ssh/exit_scripts/${HOSTNAME}"
# Host-specific script goes here
echo "I'm on $(hostname)"
HEREDOC

$ function ssh () { command ssh "$@"; source "${HOME}/.ssh/exit_scripts/${HOSTNAME}"; }