Configuring the default timeout for the SSH agent
If you're calling ssh-add
on the command line, make a shell alias. Put the following line in your ~/.bashrc
(if using bash) or ~/.zshrc
(if using zsh) or other applicable shell initialization file:
alias ssh-add='ssh-add -t 1h'
If you want to add a non-expiring key, use \ssh-add /path/to/key
or ssh-add -t 0 /path/to/key
.
If ssh-add
is being called from other program, see if they can be configured to take arguments. Failing that, create a file early on your $PATH
(~/bin
is a common choice of directory, make sure it's at the beginning of your PATH
and create it if it doesn't exist) called ssh-add
containing
#!/bin/sh
exec /usr/bin/ssh-add -t 1h "$@"
(Replace /usr/bin/ssh-add
by the path to the ssh-add
binary as necessary.)
The default timeout is forever. It is however possible to set the default timeout for a specific agent through the -t
option of ssh-agent
.
from man ssh-agent
:
-t life
Set a default value for the maximum lifetime of identities added
to the agent. The lifetime may be specified in seconds or in a
time format specified in sshd_config(5). A lifetime specified
for an identity with ssh-add(1) overrides this value. Without
this option the default maximum lifetime is forever.
AFAIK, there is no configuration in sshd_config
or ssh_config
to specify the time out for ssh-agent
. From openssh
source code, file ssh-agent.c
:
/* removes expired keys and returns number of seconds until the next expiry */
static time_t
reaper(void)
{
time_t deadline = 0, now = monotime();
Identity *id, *nxt;
int version;
Idtab *tab;
for (version = 1; version < 3; version++) {
tab = idtab_lookup(version);
for (id = TAILQ_FIRST(&tab->idlist); id; id = nxt) {
nxt = TAILQ_NEXT(id, next);
if (id->death == 0)
continue;
if (now >= id->death) {
debug("expiring key '%s'", id->comment);
TAILQ_REMOVE(&tab->idlist, id, next);
free_identity(id);
tab->nentries--;
} else
deadline = (deadline == 0) ? id->death :
MIN(deadline, id->death);
}
}
if (deadline == 0 || deadline <= now)
return 0;
else
return (deadline - now);
}
And in process_add_identity
function:
process_add_identity(SocketEntry *e, int version)
{
....
if (lifetime && !death)
death = monotime() + lifetime;
....
}
lifetime
is a global variable and only change value when parsing argument:
/* Default lifetime in seconds (0 == forever) */
static long lifetime = 0;
int
main(int ac, char **av)
{
....
case 't':
if ((lifetime = convtime(optarg)) == -1) {
fprintf(stderr, "Invalid lifetime\n");
usage();
}
....
}
If you use Ubuntu, you can set default options for ssh-agent
in /etc/X11/Xsession.d/90x11-common_ssh-agent
:
STARTSSH=
SSHAGENT=/usr/bin/ssh-agent
SSHAGENTARGS="-t 1h"
if has_option use-ssh-agent; then
if [ -x "$SSHAGENT" ] && [ -z "$SSH_AUTH_SOCK" ] \
&& [ -z "$SSH2_AUTH_SOCK" ]; then
STARTSSH=yes
if [ -f /usr/bin/ssh-add1 ] && cmp -s $SSHAGENT /usr/bin/ssh-agent2; then
# use ssh-agent2's ssh-agent1 compatibility mode
SSHAGENTARGS=-1
fi
fi
fi
if [ -n "$STARTSSH" ]; then
STARTUP="$SSHAGENT $SSHAGENTARGS ${TMPDIR:+env TMPDIR=$TMPDIR} $STARTUP"
fi