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 [email protected].

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.

Solution 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
   

Solution 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

Solution 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.

Solution 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.

Solution 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.

View more solutions

Comments

[Nethan]

What about typeset -p SSH_AUTH_SOCK?

[Rich]

@Mikel bash: typeset: SSH_AUTH_SOCK: not found from within ssh/tmux. I'll try it locally tonight, if necessary.

[Rich]

@Mikel I've added that command's output to the question.

[Blaisorblade]

AFAIK, question and answers are not OS X-specific. That's relevant to avoid some non-OS X-specific dups, namely superuser.com/q/334975/46794 and superuser.com/q/479796/46794.

[Rich]

@Blaisorblade I was under the impression my passphrase was stored in the OS X keychain (Although I can't remember now why I believed that to be the case). Is that incorrect?

[Rich]

I added the response to these commands to the question. I've also realised that the problem also occurs when I login over ssh (without using tmux), and have edited the question accordingly.

[Nethan]

ssh is easy. Turn agent forwarding on. Easiest way to do that is run ssh -A instead of ssh. Use an alias so you don't have to type it every time, or put it in your .SSH/config.

[Rich]

Cool, thanks. That worked for ssh. Any ideas how to fix it in tmux?

[Chris Johnsen]

This is the appropriate method for getting those values into a tmux session, but all of those environment variables should already be included in the default value of update-environment. The OP should check their update-environment value and possibly update wherever it is already being changed.

[Trevor Powell]

Hm.. after digging further, I agree -- the settings I listed are already in the defaults, and if I run tmux without a .tmux.conf file, everything works properly. And if I remove the line I quoted from my .tmux.conf file, that is working for me as well, although it didn't before. There's clearly something else going wrong occasionally. Maybe to do with suspend/restore or attach/detach or sshing into a tmux session remotely. I'll keep my eyes open and update if I find the factor which makes it reproducible.

[Rich]

update-environment is set correctly. However, the problem still occurs.

[Tobias Kienzler]

The problem with this is that config will only be re-executed when no tmux server is present, defying the purpose of re-attaching... Maybe there is a command line switch to re-update those variables?

[Rich]

I accepted this answer rather than any of the others that might work because it doesn't required SSH agent forwarding, which is better for my purposes. Thanks!

[Arthur Sult]

fanatastic! Thanks!