Updating SSH_AUTH_SOCK in an already established tmux session

ssh_auth_sock.md

I found this information somewhere on StackOverflow but I forgot exactly where. I'm paraphrasing what I learned here, for future reference.

SSH uses a Unix socket to communicate with other processes. The socket's path can be found by looking at the environment variable $SSH_AUTH_SOCK. When you re-connect to a tmux session that was started during a previous SSH session, this variable will contain the path of the previous SSH auth socket, and this will cause processes that try to connect to your authentication agent to fail. To fix this, we have to

1. Create a symlink from the auth socket to a fixed path somewhere, so that we can refer to it later on. In ~/.ssh/rc, add

if test "$SSH_AUTH_SOCK"; then
	ln -sf $SSH_AUTH_SOCK ~/.ssh/ssh_auth_sock
fi

2. On attaching to a tmux session, set SSH_AUTH_SOCK to the path we just created. In ~/.tmux.conf, add

setenv -g SSH_AUTH_SOCK $HOME/.ssh/ssh_auth_sock
set -g update-environment -r

FYI, I found I only needed to do

set -g update-environment -r

in ~/.tmux.conf so everytime I attach it resets the SSH_AUTH_SOCK from the incoming shell.

usage: set-option [-agosquw] [-t target-session|target-window] option [value]

@koshatul what version of tmux are you using?

tmux 2.6 on Ubuntu 18.04

$ tmux -V
tmux 2.6

$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 18.04.3 LTS
Release:	18.04
Codename:	bionic

FYI I believe your ~/.ssh/rc will not work if you open multiple SSH sessions and close the most recent one. Your symlink would point to a path that is no longer valid.

This worked for me. Just note that for byobu, the path to the .tmux.conf is ~/.byobu/.tmux.conf.