How can I check if ssh-agent is already running in Bash?

To check if ssh-agent is already running in Bash?

Here's what works for me:

if ps -p $SSH_AGENT_PID > /dev/null then echo "ssh-agent is already running" # Do something knowing the pid exists, i.e., the process with $PID is running else eval `ssh-agent -s` fi 

This was taken from here

Use:

ps -p $SSH_AGENT_PID > /dev/null || eval "$(ssh-agent -s)" 

It is a single-line command. Run for the first time, it will start ssh-agent. Run for the second time, it will not start the ssh-agent. It is simple and elegant, mate!

If you want it to be killed right after the script exits, you can just add this after the eval line:

trap "kill $SSH_AGENT_PID" exit 

Or:

trap "ssh-agent -k" exit 

$SSH_AGENT_PID gets set in the eval of ssh-agent -s.

You should be able to find running ssh-agents by scanning through /tmp/ssh-* and reconstruct the SSH_AGENT variables from it (SSH_AUTH_SOCK and SSH_AGENT_PID).

Using $SSH_AGENT_PID can only test the ssh-agent, but it misses identities when they are not yet added:

$ eval `ssh-agent` Agent pid 9906 $ echo $SSH_AGENT_PID 9906 $ ssh-add -l The agent has no identities. 

So it would be safe to check it with ssh-add -l with an expect script, like the example below:

$ eval `ssh-agent -k` Agent pid 9906 killed $ ssh-add -l Could not open a connection to your authentication agent. $ ssh-add -l &>/dev/null $ [[ "$?" == 2 ]] && eval `ssh-agent` Agent pid 9547 $ ssh-add -l &>/dev/null $ [[ "$?" == 1 ]] && expect $HOME/.ssh/agent spawn ssh-add /home/user/.ssh/id_rsa Enter passphrase for /home/user/.ssh/id_rsa: Identity added: /home/user/.ssh/id_rsa (/home/user/.ssh/id_rsa) $ ssh-add -l 4096 SHA256:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX /home/user/.ssh/id_rsa (RSA) 

So when both ssh-agent and ssh-add -l are used to run in a Bash script:

#!/bin/bash ssh-add -l &>/dev/null [[ "$?" == 2 ]] && eval `ssh-agent` ssh-add -l &>/dev/null [[ "$?" == 1 ]] && expect $HOME/.ssh/agent 

then it would always check and assuring that the connection is running:

$ ssh-add -l 4096 SHA256:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX /home/user/.ssh/id_rsa (RSA) 

You can also emulate the repeating of commands in the above script with do while.

Regarding finding running ssh-agents, previous answers either don't work or rely on a magic file like $HOME/.ssh_agent. These approaches require us to believe that user never run agents without saving their output to this file.

My approach instead relies on a rarely changed default UNIX domain socket template to find an accessible ssh-agent among available possibilities.

# (Paste the below code to your ~/.bash_profile and ~/.bashrc files) C=$SSH_AUTH_SOCK R=n/a unset SSH_AUTH_SOCK for s in $(find $C /tmp/ssh-*/agent.* -user "${USER}" 2>/dev/null | sort -u) ; do if SSH_AUTH_SOCK=$s ssh-add -l 2>/dev/null >/dev/null ; then R=$? ; else R=$? ; fi case "$R" in 0|1) export SSH_AUTH_SOCK=$s ; break ;; esac done if ! test -S "$SSH_AUTH_SOCK" ; then eval $(ssh-agent -s) unset SSH_AGENT_PID R=1 fi echo "Using $SSH_AUTH_SOCK" if test "$R" = "1" ; then ssh-add fi 

In this approach, SSH_AGENT_PID remains unknown, since it is hard to deduce it for non-roots. I assume it is actually not required for users since they don't normally want to stop agents. On my system, setting SSH_AUTH_SOCK is enough to communicate with agent for e.g. passwordless authentication. The code should work with any shell-compatible shell.

The accepted answer did not work for me under Ubuntu 14.04 (Trusty Tahr).

The test to check if the ssh-agent is running I have to use is:

[[ ! -z ${SSH_AGENT_PID+x} ]] 

And I am starting the ssh-agent with:

exec ssh-agent bash 

Otherwise the SSH_AGENT_PID is not set.

The following seems to work under both Ubuntu 14.04 and 18.04.

#!/bin/bash sshkey=id_rsa # Check ssh-agent if [[ ! -z ${SSH_AGENT_PID+x} ]] then echo "[OK] ssh-agent is already running with pid: "${SSH_AGENT_PID} else echo "Starting new ssh-agent..." `exec ssh-agent bash` echo "Started agent with pid: "${SSH_AGENT_PID} fi # Check ssh-key if [[ $(ssh-add -L | grep ${sshkey} | wc -l) -gt 0 ]] then echo "[OK] SSH key already added to ssh-agent" else echo "Need to add SSH key to ssh-agent..." # This should prompt for your passphrase ssh-add ~/.ssh/${sshkey} fi 

Here is my current ssh-agent.sh checker/launcher script that works for me on Linux and OS X.

The following block is my $HOME/.bash.d/ssh-agent.sh file:

function check_ssh_agent() { if [ -f $HOME/.ssh-agent ]; then source $HOME/.ssh-agent > /dev/null else # No agent file return 1 fi if [[ ${OSTYPE//[0-9.]/} == 'darwin' ]]; then ps -p $SSH_AGENT_PID > /dev/null # Gotcha: does not verify the PID is actually an ssh-agent # just that the PID is running return $? fi if [ -d /proc/$SSH_AGENT_PID/ ]; then # Verify the PID directory is actually an agent grep ssh-agent /proc/$SSH_AGENT_PID/cmdline > /dev/null 2> /dev/null; if [ $? -eq 0 ]; then # Yep - that is an agent return 0 else # Nope - that is something else reusing the PID return 1 fi else # Agent PID directory does not exist: Dead agent return 1 fi } function launch_ssh_agent() { ssh-agent > $HOME/.ssh-agent source $HOME/.ssh-agent # Load up all the public keys for I in $HOME/.ssh/*.pub ; do echo adding ${I/.pub/} ssh-add ${I/.pub/} done } check_ssh_agent if [ $? -eq 1 ];then launch_ssh_agent fi 

I launch the above from my .bashrc file file using:

if [ -d $HOME/.bash.d ]; then for I in $HOME/.bash.d/*.sh; do source $I done fi 

I hope this helps others get up and going quickly.

I created a public gist if you want to hack/improve this with me: ssh-agent checker/launcher

Here is a very simple command to check how many processes are running for ssh-agent (or any other program):

pidof ssh-agent 

Or:

pgrep ssh-agent 

And a very simple command to kill all processes of ssh-agent (or any program):

kill $(pidof ssh-agent) 

cat /usr/local/bin/ssh-agent-pro << 'EOF' #!/usr/bin/env bash SSH_AUTH_CONST_SOCK="/var/run/ssh-agent.sock" if [[ x$(wc -w <<< $(pidof ssh-agent)) != x1 ]] || [[ ! -e ${SSH_AUTH_CONST_SOCK} ]]; then kill -9 $(pidof ssh-agent) 2>/dev/null rm -rf ${SSH_AUTH_CONST_SOCK} ssh-agent -s -a ${SSH_AUTH_CONST_SOCK} 1>/dev/null fi echo "export SSH_AUTH_SOCK=${SSH_AUTH_CONST_SOCK}" echo "export SSH_AGENT_PID=$(pidof ssh-agent)" EOF echo "eval \$(/usr/local/bin/ssh-agent-pro)" >> /etc/profile . /etc/profile 

then you can ssh-add xxxx once, you can use ssh-agent everytime when you login.

I've noticed that having a running agent is not enough because sometimes, the SSH_AUTH_SOCK variable is set or pointing to a socket file that does not exist anymore.

Therefore, to connect to an already running ssh-agent on your machine, you can do this:

$ pgrep -u $USER -n ssh-agent -a 1906647 ssh-agent -s $ ssh-add -l Could not open a connection to your authentication agent. $ test -z "$SSH_AGENT_PID" && export SSH_AGENT_PID=$(pgrep -u $USER -n ssh-agent) $ test -z "$SSH_AUTH_SOCK" && export SSH_AUTH_SOCK=$(ls /tmp/ssh-*/agent.$(($SSH_AGENT_PID-1))) $ ssh-add -l The agent has no identities. 

On Mac, I had the same issue as the OP, and I had multiple identities set up and when I was running git push (even without any local changes) I saw an error message:

git push 

Output:

ERROR: Write access to repository not granted. fatal: Could not read from remote repository. 

It turns out the issues that I had were twofold:

1. When I ran ssh-add -l, I could see there was an extraneous identity. I.e., one which didn't exist anymore. That is, I thought I deleted it earlier, but it was still registered on ssh-agent.

2. I had too many running ssh-agent processes (normally there should only be 1-2 running) when I ran pgrep ssh-agent.

The fact is the solution was rather simple. First, it is helpful to authorize the SSH key on GitHub.

If using Enterprise Cloud, you might need to authorize the SSH key for use with SAML.

Under Settings → SSH and GPG keys on your target GitHub account, find your SSH key and ensure SSO is enabled.

Choose Configure SSO and Authorize; see image below.

Next, to be safe, I closed most, if not all, open terminal windows.

Then to kill all those running ssh-agent processes, I ran:

kill $(pgrep ssh-agent) 

Then, I started a new window and when it said:

ssh-add -l 

Output:

The agent has no identities 

If SSH_AUTH_SOCK is unset, you might need to first start up ssh-agent. Note tthat I didn't need to run this command myself.

test -z "$SSH_AUTH_SOCK" && eval "$(ssh-agent -s)" 

I just add them back with ssh-add:

ssh-add ~/.ssh/id_ed25519_<user> 

I can confirm that ssh-add -l now lists all identities after restarting a new terminal window.

If anyone still runs into issues, there could be a problem with the clone or push URL for a project. For example, using HTTPS instead of SSH.

Note that insteadOf in the Git configuration does not chain. This post (along with its answer) might be helpful.

I made this Bash function to count and return the number of running ssh-agent processes... It searches ssh-agent process using procfs instead of using ps -p $SSH_AGENT_PID:cmd or $SSH_AUTH_SOCK:var ... (these environment variables can still be set with old values while ssh-agent's process is already killed: if ssh-agent -k or $(ssh-agent -k) instead of eval $(ssh-agent -k))

function count_agent_procfs(){ declare -a agent_list=( ) for folders in $(ls -d /proc/*[[:digit:]] | grep -v /proc/1$);do fichier="${folders}/stat" pid=${folders/\/proc\//} [[ -f ${fichier} ]] && [[ $(cat ${fichier} | cut -d " " -f2) == "(ssh-agent)" ]] && agent_list+=(${pid}) done return ${#agent_list[@]} } 

...and then if there is a lot of ssh-agent process running you get their PID with this list..."${agent_list[@]}"

The answer from AndrewD was the most helpful for me in most cases, but I found out that when $SSH_AGENT_PID is not set or present, the ps command will respond with the error:

error: list of process IDs must follow -p 

To fix this, we need to check the existence of the $SSH_AGENT_PID variable, so that the condition case will now be:

if [ -n "$SSH_AGENT_PID" ] && ps -p "$SSH_AGENT_PID" > /dev/null 

The entire modified snippet:

if [ -n "$SSH_AGENT_PID" ] && ps -p "$SSH_AGENT_PID" > /dev/null then echo "ssh-agent is already running" # Do something knowing the pid exists, i.e., the process with $PID is running else eval `ssh-agent -s` fi 

Shorter and revised version:

if ! [ -n "$SSH_AGENT_PID" ] || ! ps -p "$SSH_AGENT_PID" > /dev/null then eval "$(ssh-agent -s)" fi ssh-add ~/.ssh/github_ed25519 

You can modify line #1 to:

PID_SSH_AGENT=`eval ssh-agent -s | grep -Po "(?<=pid\ ).*(?=\;)"` 

And then at the end of the script you can do:

kill -9 $PID_SSH_AGENT