This item inspired by Ken. And in order to keep this answer relatively short, I have to skip a bunch of pre-reqs. I’m going to assume that you understand service startup and run-levels in Linux, and maybe have tried specifying start-order in RedHat… This is where my thinking went when answering the question for Ken, so that’s what you get here. Anyway, back to the question at hand…
You don’t. 😉 Just kidding… *kinda*…
So you already know how to cause services to start and stop at various runlevels using the
chkconfig tool on RedHat (and the RedHat derivatives, which I just refer to as RedHat) and Suse, or the
insserv tool on Suse. But *now* what you want to do is enforce the service load sequence by number.
“Ah-hah!”, you say, because you are an old-school Unix guy (yes, Your Linux Guy knows about you and your ways 😉 ), and you know that all you have to do is hand-write a script, and throw it (or a symlink) into the appropriate
rc[?].d directory, right? Wrong. Well, you *could* do that, but as soon as you run
chkconfig on Suse, it will re-order your service based on some other criteria… more on that in a moment.
First some background on RedHat…
Many of you are used to the tool
chkconfig. In order to specify load order in RedHat, you make sure that one important line similar to the following exists in the start script in the
# chkconfig: 35 98 01
…note that the leading pound/hash symbol indicates that it is a comment; this is important. Then, after the
chkconfig:, the next items are as follows: runlevels in which to start (3 and 5), start sequence number (98, which is very late in the order), and stop/kill sequence number (01). Yours, of course, will vary. And — very important here, folks — you need to run
chkconfig after your modifications for it to take effect; it goes through and reads all those comments and places things in the appropriate place.
Now, on to the Suse
Suse uses a similar philosophy to RedHat’s
insserv only insofar as there are a certain set of comments in the start script required to enforce start order. However, instead of you having the luxury of being able to specify *the exact number* for the startup script, you only get to specify things that should be started *before* or *after* your script. This will effectively do the same thing with the arrangement, though you might not get the pretty number
S98 you were hoping for.
So, specifically, here is an example comment block with just a reasonable minimum, for a fake application called
### BEGIN INIT INFO
# Provides: myapp
# Required-Start: $ALL
# Default-Start: 3 5
# Default-Stop: 0 1 2 4 6
# Description: My App is cool
# Short-Description: My App
### END INIT INFO
…this example will cause
myapp to be one of the last things loaded (the
$ALL is a special value, see below), in
runlevel 3 or 5, and will stop at all other levels. On my machine, it puts
S21, right before
S21SuSEfirewall2_setup, which is numerically equal, but alphabetically later. And — just like with RedHat — you must run
chkconfig or the Suse tool
insserv for the scripts to be re-arranged and placed, ready to run. Its important to remember that on Suse,
chkconfig is just a child to
insserv, it is not the same exact tool as on RedHat. But like on RedHat, it will parse the comments fields and place the script in the appropriate places.
Now here’s how that actually works on Suse…
For Suse, the “Provides:” item in the script creates something called a “facility”. So in my example above, I’ve created a facility called “
myapp“. Then, others scripts can reference that facility in specifying whether they should load before or after. For example, the
sshd startup script provides a “
sshd” facility (it does not have to be the same name as the daemon), so I could have put the following in my
# Required-Start: $sshd
myapp would have been placed to start right after
sshd in the appropriate
/etc/init.d/rc[?].d directory. On my machine,
sshd is at
S12… so if I did that,
myapp would likely be at
S13 (the next higher number). Note that the facility is prefixed by a dollar-sign when it referenced/called, but not when it is created in the “
Provides:” line. Also, the
$ALL is a special all-inclusive facility value that means “all facilities”, and when used, it causes your script to be loaded after all others.
Warning: Some of the startup scripts in Suse have the RedHat
chkconfig syntax in them. Why? To mess with you. No, not really, but that’s what it did to me when I was first figuring this stuff out. Especially since Suse has the
chkconfig binary (which works on Suse to a lesser extent than on RedHat) for your convenience… and confusion…
Phew! Got it? Good.
Make sure to let me know if I missed something…