How can I get ssh-agent working over ssh and in tmux (on OS X)?

Question

I have a private key set up for my github account, the passphrase to which is, I believe, stored in OS X's keychain. I certainly don't have to type it in when I open a terminal window and enter ssh [e-mail].

However, when I'm running bash over an ssh session, or locally inside a tmux session, I have to type in the passphrase every single time I attempt to ssh to github.

This question suggests that a similar problem exists with screen, but I don't really understand the issue well enough to fix it in tmux. There's also this page which includes a fairly complicated solution, but for zsh.

EDIT:

In response to @Mikel's answer, from a local terminal I get the following output:

[~]
$ echo $SSH_AUTH_SOCK
/tmp/launch-S4HBD6/Listeners
[~] 
$ ssh-add -l
2048 [my key fingerprint] /Users/richie/.ssh/id_rsa (RSA)
[~]
$ typeset -p SSH_AUTH_SOCK
declare -x SSH_AUTH_SOCK="/tmp/launch-S4HBD6/Listeners"

Whereas over ssh or in tmux I get:

[~]
$ echo $SSH_AUTH_SOCK

[~]
$ ssh-add -l
Could not open a connection to your authentication agent.
[~]
$ typeset -p SSH_AUTH_SOCK
bash: typeset: SSH_AUTH_SOCK: not found

echo $SSH_AGENT_PID returns nothing whatever shell I run it from.

Answer 1

My colleague created some bash functions to assist with finding a live agent: https://github.com/wwalker/ssh-find-agent

He uses it mainly for connecting between systems (laptop to desktop, etc), but I use it most often for local tmux sessions where you logout/in from your window manager (OS X for myself).

Usage

1. Download ssh-find-agent.bash (git clone git://github.com/wwalker/ssh-find-agent.git works).

2. Add the following to ~/.bashrc:

   . /path/to/ssh-find-agent.bash
   

3. Then you can type the following to set SSH_AUTH_SOCK in your current shell:

   set_ssh_agent_socket
   

Answer 2

An elegant solution, picked up from dagit.o:

Create ~/.ssh/rc

#!/bin/bash
if [ -S "$SSH_AUTH_SOCK" ]; then
    ln -sf $SSH_AUTH_SOCK ~/.ssh/ssh_auth_sock
fi

Add to ~/.tmux.conf

set -g update-environment "DISPLAY SSH_ASKPASS SSH_AGENT_PID SSH_CONNECTION WINDOWID XAUTHORITY"
set-environment -g 'SSH_AUTH_SOCK' ~/.ssh/ssh_auth_sock

Answer 3

In your .tmux.conf configuration file, add this line:

set -g update-environment "SSH_ASKPASS SSH_AUTH_SOCK SSH_AGENT_PID SSH_CONNECTION"

This causes these environment variables to be copied from your main shell to any shells opened within tmux, which then allows ssh-agent to work properly within those tmux shells.

Answer 4

It happened to me that panes created when connecting via ssh from OS X started asking my passphrase after a while of working ok. I found a way to fix that stealing this line from http://santini.di.unimi.it/extras/ph/my-tmux-setup.html

eval $(tmux show-environment -t [YOUR-SESSION] | grep '^SSH_AUTH_SOCK')

Just run it from the pane that's complaining.

Answer 5

Not sure if you are using bash or another shell, but this guy's tmux setup looks like it would work for bash. Personally, I am using zsh with oh-my-zsh, and I found that ssh-agent started working in tmux after I added

zstyle :omz:plugins:ssh-agent agent-forwarding on

to my .zshrc file and reloaded the config in my running zsh sessions. I also found this guy's zsh-oriented solution, but it turned out to be unnecessary for me.

Answer 6

What does:

echo $SSH_AUTH_SOCK
echo $SSH_AGENT_PID
ssh-add -l

print?

Run it in your normal terminal, then run it inside your tmux session. They should print the same thing.

Answer 7

There are many solutions, but the simplest one is found in Hans Ginzel's answer, dated 8 January 2016, to a related StackOverflow question dated 27 January 2014. Simply add the following to your shell ~/.profile or similar:

alias ssh='eval $(tmux show-env -s | grep "^SSH_") && ssh'

There is no need to define multi-line functions or create new temporary files. If you don't want to alias ssh, simply change it to fixssh and remove && ssh at the end, and run fixssh whenever you're trying to run ssh from inside a reattached tmux session.

The answer by Hans Ginzel suggests that a 'newer version' of tmux is required to run show-env -s. This works for me in tmux 2.7, and on my reading of the changelog, -s was added on 3 June 2008 just before the release of tmux 0.3. tmux 2.3 (29 September 2016) is in Debian stable.