Automatically start a single instance of ssh-agent for all terminal sessions to share (bash)

README.md

Installation

1. mkdir -p ~/.config && touch ~/.config/ssh-agent.pid
2. Paste the contents of ssh-agent-manage.sh into your .bashrc or .bash_profile or similar
3. killall -9 ssh-agent
4. Start a new terminal session (note: old sessions will not see ssh-agent, only new ones)

Details

This snippet, when included in .bashrc, will ensure that your session has a working ssh-agent with all your ssh keys loaded into it. It does this without creating separate ssh-agent processes by:

• Using ~/.config/ssh-agent.socket as the socket, rather than a random-named temporary socket
• Tracking the PID of ssh-agent in ~/.config/ssh-agent.pid
• setting up the appropriate environment variables to point to any already-running ssh-agent started this way (NB: if you start an agent process by hand, this won't know about it)
• starting up an ssh-agent if it can't find a properly-configured version already running

ssh-agent-manage.sh

# SSH agent
ssh_pid_file="$HOME/.config/ssh-agent.pid"
SSH_AUTH_SOCK="$HOME/.config/ssh-agent.sock"
if [ -z "$SSH_AGENT_PID" ]
then
	# no PID exported, try to get it from pidfile
	SSH_AGENT_PID=$(cat "$ssh_pid_file")
fi

if ! kill -0 $SSH_AGENT_PID &> /dev/null
then
	# the agent is not running, start it
	rm "$SSH_AUTH_SOCK" &> /dev/null
	>&2 echo "Starting SSH agent, since it's not running; this can take a moment"
	eval "$(ssh-agent -s -a "$SSH_AUTH_SOCK")"
	echo "$SSH_AGENT_PID" > "$ssh_pid_file"
	ssh-add -A 2>/dev/null

	>&2 echo "Started ssh-agent with '$SSH_AUTH_SOCK'"
# else
# 	>&2 echo "ssh-agent on '$SSH_AUTH_SOCK' ($SSH_AGENT_PID)"
fi
export SSH_AGENT_PID
export SSH_AUTH_SOCK

Thank you for the snippets and the guide. But ssh-add doesn't recognize -A.

@soundlake -- newer versions of ssh-add on macOS have deprecated -A in favor of --apple-load-keychain ; you can either swap that out or add export APPLE_SSH_ADD_BEHAVIOR=macos to your environment

Thank you for your comment. I didn't know -A was deprecated on MacOS, because I don't use it. But I do know it is removed (not deprecated) on my WSL Debian (unstable) although I don't know when.

I did a workaround with simple bash script to traverse the directory to add all keys.

This will fail if the directory for $SSH_AUTH_SOCK doesn't exist. You'll probably only run into this error on a fresh install, or if you modify the path for SSH_AUTH_SOCK. Worth noting you may want to add a mkdir -p "$HOME/.config" near the start of the script, with adjustments if you do modify the path, just in case.

Thanks for the gist of it!