0

I have a host that doesn't have the termcap entries for non-standard terminals and I cannot add them (policy).

I use tmux which sets a terminal type to something that this device does not recognise. No issue here, worst case I can set the TERM to 'xterm' and be done with it. But:

I've configured some defaults for the OpenSSH client, among other settings, I instructed it to not send any environment variables other than LANG and LC_*.

The relevant part of ~/.ssh/config:

Host *
  SendEnv LANG LC_*

My OpenSSH client version is 6.6.1.

Here's the transcript of my SSH session with irrelevant lines removed:

% TERM=you.shall.not.pass ssh -vvv host
...
debug1: Connection established.
...
debug1: Authentication succeeded (publickey).
...
debug1: Sending environment.
...
debug1: Sending env LANG = en_GB.UTF-8
debug2: channel 0: request env confirm 0
...
debug3: Ignored env TERM

As per the above, it sent LANG, wrote it ignored TERM but yet somehow it has propagated to the remote host:

root@host% echo $TERM
you.shall.not.pass

Is this something you've come across? It's not a major issue but I thought that unless I'm doing something wrong, this is inconsistent with the documentation.

1

Ssh doesn't pass the value of TERM as an environment variable per se. The SSH protocol message for requesting a pseudo-terminal (PTY) has a field for the terminal type, along with things like the terminal's width and height. See RFC 4254, Section 6.2.

Try running a command without a PTY, and you'll probably get different results, for example:

$ TERM=foo ssh localhost 'echo $TERM'
dumb
  • Thanks a lot for the link to the RFC - this makes sense now. – Marcin Kaminski Sep 7 '14 at 22:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.