While most desktop Linux OS’s have decent support for ssh-agent, it may be something you have to add to certain Linux or *BSD disto’s. I’ve been using the following to load my private key(s) the first time I login, and hold them in memory for subsequent sessions.

SSH_ENV="$HOME/.ssh/environment"

function start_agent {
echo "Initialising new SSH agent..."
(umask 066; /usr/bin/ssh-agent > "${SSH_ENV}")
. "${SSH_ENV}" > /dev/null
/usr/bin/ssh-add;
}

# Source SSH settings, if applicable

if [ -f "${SSH_ENV}" ]; then
. "${SSH_ENV}" > /dev/null
ps -ef | grep ${SSH_AGENT_PID} | grep ssh-agent$ > /dev/null || {
start_agent;
}
else
start_agent;
fi

if [ -z "$SSH_AUTH_SOCK" ]; then
eval ssh-agent -s ssh-add
fi

/etc/rc.conf:

ifconfig_em0="up promisc mtu 9212"
ifconfig_em1="up promisc mtu 9212"
cloned_interfaces="lagg0"
ifconfig_lagg0="laggproto loadbalance laggport em0 laggport em1 promisc monitor up mtu 9212"


usage: tcpdump -i lagg0 …