[Box-Admins] How does Jenkins start?

[Ken Causey]

> -------- Original Message --------
> Subject: Re: [Box-Admins] How does Jenkins start?
> From: "David T. Lewis" <lewis at mail.msen.com>
> Date: Sun, February 09, 2014 1:30 pm
> To: Squeak Hosting Support <box-admins at lists.squeakfoundation.org>
> 
> 
> 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

The more modern way now is to use the service command.

# service jenkins stop

and FYI

# service jenkins

will, assuming the standard is followed, provide a short help comment
listing the applicable commands.

> 
> 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.

I'm not on the system now to check but if you read the jenkins startup
script you may find that configuration variable, including blocking it
from starting may be adjustable via a file in /etc/default/.  The trend
is towards getting away from modifying /etc/init.d/ scripts directly.

> 
> Dave