If you'd like to ensure only one instance of ssh-agent is working in background, add this to your .bashrc (or .zshrc if you are using zsh):
function setup_ssh_agent {
local SSH_AGENT_DATA
local SSH_AGENT_RUN_NEW
local SSH_AGENT_CMD_LINE
# If there is no active agent
if [ -z "$SSH_AUTH_SOCK" ]; then
# See if there is session from previous ssh-agent run
SSH_AGENT_DATA=$(2>/dev/null cat ~/.ssh_agent_data)
if [ $? != 0 ]; then
# If there is no previous session, run ssh-agent
SSH_AGENT_RUN_NEW=1
else
# Load previous session var
eval "$SSH_AGENT_DATA" > /dev/null
# If agent is not set or it is dead, run ssh-agent
SSH_AGENT_CMD_LINE=$(2>/dev/null tr '\0' ' ' < /proc/$SSH_AGENT_PID/cmdline)
if [ $? != 0 ] || [ "$SSH_AGENT_CMD_LINE" != "ssh-agent -s " ] || [ -z "$SSH_AUTH_SOCK" ] || [ ! -e "$SSH_AUTH_SOCK" ]; then
SSH_AGENT_RUN_NEW=1
fi
fi
# Run new ssh-agent if needed
if [ "$SSH_AGENT_RUN_NEW" == 1 ]; then
SSH_AGENT_DATA=`ssh-agent -s`
eval "$SSH_AGENT_DATA" > /dev/null
# Save configuration for next terminal sessions
echo "$SSH_AGENT_DATA" > ~/.ssh_agent_data
# Set file's permission to user r/w only
chmod 600 ~/.ssh_agent_data
fi
fi
}
setup_ssh_agent # Don't forget to call above function!
To automatically add keys when you use them with ssh, use AddKeysToAgent configuration. To forward your ssh-agent to sessions you access through ssh, use ForwardAgent option.
Example configuration from .ssh/config for these two:
Host *
AddKeysToAgent yes
ForwardAgent yes
This should be enough for a nice working ssh-agent!
Note 1: Forwarding your agent in all ssh sessions may not be secure. You may want to use spesific hostnames for ForwardAgent in your config, instead of a wildcard hostname. Same goes with AddKeysToAgent configuration.
Note 2: This gist assumes that you need just one ssh-agent. You may use multiple ssh-agent to keep separate set of keys, which is an advanced use of ssh-agent. This gist does not handle this case.