[Box-Admins] How does Jenkins start?

[David T. Lewis]

On Sun, Feb 09, 2014 at 11:57:23AM -0700, Ken Causey wrote:
> > -------- Original Message --------
> > Subject: [Box-Admins] How does Jenkins start?
> > From: Frank Shearar <frank.shearar at gmail.com>
> > Date: Sun, February 09, 2014 6:49 am
> > To: Squeak Hosting Support <box-admins at lists.squeakfoundation.org>
> > 
> > 
> > I see all too often that builds fail because the JVM process runs out
> > of PermGen space. Up until today I'd assumed that was a problem on the
> > build agents. However, today I bounced my Mac mini (latest victim of
> > this problem) and... nothing happened. But when I bounced _Jenkins_
> > the build succeeded.
> > 
> > Jenkins, being a Java process, does have a bunch of knobs that can be
> > used to adjust GC. How does Jenkins get started? What keeps it
> > running?
> > 
> > Or, meta-question, how can I find this out for myself, and reduce the
> > noise on the list? :)
> > 
> > frank
> 
> I'm not aware of any easy way to answer this without some prior
> knowledge.  But here is how I'm finding the answer:
> 
> So first of all I know we like to use DJB's daemontools sometimes which
> provides a way to start and maintain services.  If jenkins is started
> via daemontools then there will be a supervise process running with an
> argument probably called jenkins or the like which names a
> directory/link to directory under the daemontools service directory
> which is commonly found under /service/.
> 
> kencausey at box3-squeak:~$ ls -l /service/
> total 0
> lrwxrwxrwx 1 root root 14 Nov 14 03:23 ssdotcom -> /home/ssdotcom
> lrwxrwxrwx 1 root root 12 Jan  1  2013 tinydns -> /etc/tinydns
> 
> Neither of these seem relevant, so daemontools is not used.
> 
> The next lower level to check is in /etc/init.d/
> 
> kencausey at box3-squeak:~$ ls -l /etc/init.d/
> ...
> -rwxr-xr-x 1 root root  5867 Jun 25  2012 jenkins
> ...
> 
> So the basic answer is that this program/script is run by the init
> system to start jenkins.
> 

And in turn, init uses the script in /etc/init.d/ to do the work. The file
/etc/init.d/README gives an overview. In the case of jenkins, the script
/etc/init.d/jenkins does the work. You can stop the jenkins service by doing
this (as root, or with sudo):

# /etc/init.d/jenkins stop

Likewise, start and restart will do the expected.

The jenkins script will be symlinked to directories associated with various
system runlevels:

-rwxr-xr-x 1 root root 5867 Jun 25  2012 etc/init.d/jenkins
lrwxrwxrwx 1 root root   17 Oct  9  2012 etc/rc0.d/K01jenkins -> ../init.d/jenkins
lrwxrwxrwx 1 root root   17 Oct  9  2012 etc/rc1.d/K01jenkins -> ../init.d/jenkins
lrwxrwxrwx 1 root root   17 Oct 15  2012 etc/rc2.d/S03jenkins -> ../init.d/jenkins
lrwxrwxrwx 1 root root   17 Oct 15  2012 etc/rc3.d/S03jenkins -> ../init.d/jenkins
lrwxrwxrwx 1 root root   17 Oct 15  2012 etc/rc4.d/S03jenkins -> ../init.d/jenkins
lrwxrwxrwx 1 root root   17 Oct 15  2012 etc/rc5.d/S03jenkins -> ../init.d/jenkins
lrwxrwxrwx 1 root root   17 Oct  9  2012 etc/rc6.d/K01jenkins -> ../init.d/jenkins

The init system uses these (based on naming conventions) to figure out what scripts
to start and stop, and in what order, when entering or leaving a runlevel.

Don't ever edit any of this stuff directly. But it would OK to run the /etc/init.d/jenkins
script directly if you wanted to stop, start, or restart the service manually.

Dave