average admins

Originally posted at techsays.com on February 25nd, 2007.

Twice in the past week I’ve needed to start a script automatically if the server was ever rebooted.

I haven’t had to do that in quite a while so I had to look it up.

Lucky for me, a user of the JustLinux forums already answered the question for someone else. Except instead of just answering his question with a simple answer, he supplied a well written howto with great examples.

You can find his post here: http://justlinux.com/forum/showthread.php?t=40831

And if you know me, I don’t like relying on remote websites to have the information when I need it years from now. I like pulling the information down so if JustLinux crashes next month, I’ll still know how to do this.

Craig McPherson
01-11-2001, 11:31 PM
Alternate, more “standard” solutions:

If you want to run SSHD from your inetd server rather than as a standalone server (this is a good way to save memory if you’ll be accepting SSH connections only occasionally — the daemon is only started when a connection comes in, which makes the connection take a split second longer to establish, but saves memory when there’s no active SSH connection), just add an entry for it to your inetd configuration file.

For the standard inetd, in your inetd.conf:

ssh stream tcp nowait root /usr/sbin/sshd

(Adjust path accordingly, make sure “ssh” is in your /etc/services)

For xinetd, which cool people use, in your xinetd.conf:

service ssh
{
socket_type = stream
protocol = tcp
wait = no
user = root
server = /usr/sbin/sshd
}

Restart your inetd program after changing its configuration file.

The ssh program on my system claimed it needed to be passed the “-i” flag to be run from inetd, but that wasn’t my experience. If it’s required with your version of ssh, just add -i to the inetd.conf, or the line “server_args = -i” to your xinetd.conf.

If you want to run your sshd as a standalone daemon, you should make an init script for it in /etc/init.d. A very simple /etc/init.d/ssh could be just this:

#!/bin/sh
/usr/sbin/sshd&

Of course, if you were going to do something that simple, you might as well just call your init script “/etc/init.d/local”, and add any other commands that you want run at bootup to it.

Then you just go to the init directory for the runlevel you boot into (check /etc/inittab for this), ie /etc/rc2.d for runlevel 2. Now create a symlink there pointing to your init script, and call it something like “S90local” or “S90ssh”. It has to start with a capital S, and the number following that determines when during the boot process the script should be run.

A more complex init script would be something like this, from the Debian SSH package:

#! /bin/sh

# /etc/init.d/ssh: start and stop the OpenBSDh “secure shell(tm)” daemon

test -x /usr/sbin/sshd | | exit 0
( /usr/sbin/sshd -\? 2>&1 | grep -q OpenSSH ) 2>/dev/null | | exit 0

# forget it if we’re trying to start, and /etc/ssh/NOSERVER exists
if expr “$1″ : ‘.*start$’ >/dev/null && [ -e /etc/ssh/NOSERVER ]; then
echo “Not starting OpenBSD Secure Shell server (/etc/ssh/NOSERVER)”
exit 0
fi

# Configurable options:

case “$1″ in
start)
test -f /etc/ssh/sshd_not_to_be_run && exit 0
echo -n “Starting OpenBSD Secure Shell server: sshd”
start-stop-daemon –start –quiet –pidfile /var/run/sshd.pid –exec /usr/sbin/sshd
echo “.”
;;
stop)
echo -n “Stopping OpenBSD Secure Shell server: sshd”
start-stop-daemon –stop –quiet –oknodo –pidfile /var/run/sshd.pid –exec /usr/sbin/sshd
echo “.”
;;

reload|force-reload)
echo -n “Reloading OpenBSD Secure Shell server’s configuration”
start-stop-daemon –stop –signal 1 –quiet –oknodo –pidfile /var/run/sshd.pid –exec /usr/sbin/sshd
echo “.”
;;

restart)
echo -n “Restarting OpenBSD Secure Shell server: sshd”
start-stop-daemon –stop –quiet –oknodo –pidfile /var/run/sshd.pid –exec /usr/sbin/sshd
sleep 10
start-stop-daemon –start –quiet –pidfile /var/run/sshd.pid –exec /usr/sbin/sshd
echo “.”
;;

*)
echo “Usage: /etc/init.d/ssh {start|stop|reload|force-reload|restart}”
exit 1
esac

exit 0

Then symlink it as before.

Anyway, what you did broke a number of Linux and Unix standards. The Linux Standards Base people aren’t going to come to your door with a gun, but you might run into problems down the line.

1. Symlinks in the various rc boot directories (rc.boot, rcS.d, rc0-6.d) can’t point directly to binaries. They have to point to scripts, which generally in turn start binaries. Of course, nothing will break if you do this but it violates the standards.

2. You shouldn’t use rc.boot. I believe its use is deprecated and is only for backwards compatibility while programs finish switching over to the standards. rc.boot will probably be removed at some point. Use the normal runlevel rc directories (rc2.d through rc5.d) for normal stuff, rcS.d for stuff that will be started in EVERY runlevel, even single user mode (stuff like SSH should NOT start in single user mode), rc0.d and rc6.d should be used for stuff that needs to be run when shutting down or rebooting.

Clear enough?

——————
http://users.ipa.net/~cmcpher/paminv.gif DEBIAN (http://www.debian.org/) http://users.ipa.net/~cmcpher/paminv.gif
It turns girls into statues!

[This message has been edited by Craig McPherson (edited 11 January 2001).]

This entry was posted on Sunday, February 25th, 2007 at 11:53 am and is filed under How To, Linux, Open Source. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.