How to check if ssh-agent is already running in ba

Question

I have a sample sh script on my Linux environment, which basically run's the ssh-agent for the current shell, adds a key to it and runs two git commands:

#!/bin/bash
eval "$(ssh-agent -s)"
ssh-add /home/duvdevan/.ssh/id_rsa

git -C /var/www/duvdevan/ reset --hard origin/master
git -C /var/www/duvdevan/ pull origin master

Script actually works fine, but every time I run it I get a new process so I think it might become a performance issue and I might end up having useless processes out there.

An example of the output:

Agent pid 12109
Identity added: /home/duvdevan/.ssh/custom_rsa (rsa w/o comment)

Also, along with all this, is it possible to find an existing ssh-agent process and add my keys into it?

Answer 1

The accepted answer did not work for me under Ubuntu 14.04.

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

Answer 2

Using $SSH_AGENT_PID can only test the ssh-agent but miss identities when it is 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 save to check it with ssh-add -l with an expect script like 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 put to run on 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 on above script with do while

Answer 3

No, really, how to check if ssh-agent is already running in bash?

Answers so far don't appear to answer the original question...

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: https://stackoverflow.com/a/15774758

Answer 4

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

Answer 5

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).

Answer 6

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

Single line command. Run for the first time will start ssh-agent. Run for the second time will not start the ssh-agent. Simple and Elegant Mate !!!