6

In Ubuntu 16.04 I executed: 

eval $(ssh-agent) && ssh-add

I got: 

Agent pid 3361

I then SSH tunneled into my VPS successfully, after inserting my passphrase.

The problem:

Well, it's not that much of a "problem", but:

I went back to my local session with exit, and when I tried to login to my VPS again, I had to reenter my passphrase...

My question:

Why would I be asked to enter the passphrase again?

I didn't close the current session and did eval $(ssh-agent) && ssh-add, before tunneling. So, why the system won't "remember" it?

  • 1
    No comments or answers? Even with the bounty... Surprising. –  Feb 05 '17 at 22:42
  • I don't get this behavior, I get what you're expecting (second SSH connection authenticates without prompting for passphrase/password). Try running ssh-add -l before and after the working SSH connection to make sure the agent still holds the key after the first exit. Then try using ssh -vv (two v's) on your second attempt to connect so that the client will show you all the keys it's trying. – Steven K Feb 06 '17 at 04:16
  • I find using ´ssh´ with passphrase weird to begin with... – aggsol Feb 07 '17 at 08:12

2 Answers2

3

Every time you do eval $(ssh-agent) && ssh-add, a new agent starts, so you need to re-authenticate yourself to it.

I think the best way is to store the SSH agent data permanently per session (in your ~/.profile):

export SSHPROC=${HOME}/.ssh/cur-proc.${HOSTNAME}
restart_ssh_agent(){
  . ${SSHPROC}
  kill ${SSH_AGENT_PID}
  /bin/rm -rf ${SSHPROC} ${SSH_AUTH_SOCK} /tmp/ssh-*
  ssh-agent > ${SSHPROC}
  cat ${SSHPROC}
  . ${SSHPROC}
  ssh-add
}

and add . ${SSHPROC} to your .bashrc.

Then you call restart_ssh_agent once (or when it dies for some reason) and then keep your credentials with the agent.

sds
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  • I'm not sure I fully understand what you did here... I'm quite new to Linux. I should copy and paste this whole codeblock inside a heredoc each time I start a session? –  Mar 12 '17 at 02:56
  • you need to add the code which defines the function restart_ssh_agent to .profile and run it as necessary. – sds Mar 12 '17 at 04:09
2

You need to detect if ssh-agent is already running via your .bashrc. If it is not running, then start it. If it is already running, then use it.

Here's a snippet from my .bashrc which sets up environment variables for an existing session.

#
# setup ssh-agent
#
#start running ssh-agent if it is not already.
if [ ! 'root' = "${USER}" ]; then
  if ! pgrep ssh-agent &> /dev/null && ! uname -rms | grep Darwin &> /dev/null; then
    eval "$(ssh-agent -t 3600)" > /dev/null
  fi
  if ! uname -rms | grep Darwin &> /dev/null; then
    if [ -z "${SSH_AUTH_SOCK}" -o -z "${SSH_AGENT_PID}" ]; then
        #first time failed so try again.
        SSH_AUTH_SOCK="$(ls -l /tmp/ssh-*/agent.* 2> /dev/null | grep "${USER}" | awk '{print $9}' | tail -n1)"
        SSH_AGENT_PID="$(echo ${SSH_AUTH_SOCK} | cut -d. -f2)"
    fi
    if [ -z "${SSH_AUTH_SOCK}" -o -z "${SSH_AGENT_PID}" ]; then
      SSH_AUTH_SOCK="$(lsof -p "$(pgrep ssh-agent | tr '\n' ',')" | grep "${USER}" | grep -e "ssh-[^/]*/agent\.[0-9]\+$" | tr ' ' '\n' | tail -n1)"
      SSH_AGENT_PID="$(echo ${SSH_AUTH_SOCK} | cut -d. -f2)"
    fi
  fi
  [ -n "${SSH_AUTH_SOCK}" ] && export SSH_AUTH_SOCK
  [ -n "${SSH_AGENT_PID}" ] && export SSH_AGENT_PID
fi

I use that same snippet for multiple platforms and not just Mac or Linux on x86. That snippet can be further improved but for now it works for me reliably.

Sam Gleske
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