[Box-Admins] How does Jenkins start?

[Frank Shearar]

On 9 February 2014 19:56, Ken Causey <ken at kencausey.com> wrote:
>> -------- 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.

Yep :) Thanks!

>> 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.

Yep. In particular, it looks like I want to set JENKINS_ARGS
somewhere. I highly doubt that fiddling with /etc/default/jenkins is
what I want so I'll just scrabble around a bit more remembering all
I've forgotten about init.d style services.

frank

>> Dave