How do I detect if the current session is an SSH session via bash?

Question

I would like to detect whether the current user session is from an SSH connection - that is, whether the user is physically sitting at the computer that hosts the current terminal or whether he is remotely connected through SSH?

Is there an easy way to do this, preferably through a bash-scriptable method?

Answer 1

A quick way would be check if the SSH_TTY variable is set:

$ ssh lab
$ echo $SSH_TTY 
/dev/pts/22

There are a few SSH-related variables set. Two others are SSH_CLIENT and SSH_CONNECTION. Either of them could be used as well.

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Another way would be to check if an ancestor process is the sshd daemon:

$ pstree -ps $$
init(1)───sshd(1170)───sshd(14153)───sshd(14225)───bash(24232)───pstree(27281)

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Relevant reading:

• How can I detect if the shell is controlled from SSH? - a well-answered question on Unix & Linux.