[systemd-devel] making a python daemon both systemd and el5 compatible

[Greg Swift]

thanks to both Amit and Colin.  I'm going to see what we can throw
together.  Will try to remember to share back what we come up with.


On Mon, Jan 27, 2014 at 6:46 PM, Amit Saha <asaha at redhat.com> wrote:

>
>
> ----- Original Message -----
> > From: "Greg Swift" <gregswift at gmail.com>
> > To: systemd-devel at lists.freedesktop.org
> > Sent: Tuesday, January 28, 2014 3:20:46 AM
> > Subject: [systemd-devel] making a python daemon both systemd and el5
>  compatible
> >
> > I'm working on a small daemon[1] that doesn't do a whole lot, but we need
> > it to work on RHEL5+.  Going out of the gate I want to ensure it also
> works
> > with systemd, since i want it to be usable on fedora and el7.
> >
> > This stackoverflow[2] has a method, but then mentions some compatibility
> > problems with the library it recommends that seem like it will not make
> it
> > to friendly back to el5.
> >
> > In the interm I was going to try leveraging cherrypy's bits (PIDFile and
> > Daemonize), but they aren't backwards compatible to EL5, so we have to
> fix
> > that.
> >
> > I tried to find some place where this was mentioned or recommended but my
> > google-fu failed me.
> >
> > Do you have any recommendations or a existing python daemon that you
> could
> > point me at that has similar needs?
>
> The Beaker project's daemons (beakerd, beaker-proxy, beaker-watchdog and
> beaker-provision)
> adopts a policy that if it is on a distro which doesn't have
> systemd, it uses the SysV init files and vice-versa. The spec file here [1]
> should give you some idea about what we are doing.
>
> Specifically, w.r.t python-daemon, on the SO thread you mention, I had
> replied
> with my experience here [2] and I wrote further on this here [3].
>
> Specifically, this may be helpful for you:
>
> "In the [Service] section, the Type is set to Forking. This is because,
> beakerd
> uses python-daemon which forks itself (detaches itself) during the
> daemonization.
>  However, you must ensure that when creating a DaemonContext() object, you
> should
>  specify detach_process=True. This is because, if python-daemon detects
> that it
> is running under a init manager, it doesn't detach itself unless the
> keyword is
> explicitly set to True, as above (you can see the code in daemon.py).
> Hence, although not setting the above keyword would work under SysV Init,
> it doesn't
> work under systemd (with Type=Forking), since the daemon doesn't fork at
> all and
> systemd expects it to fork (and finally kills it). The PIDFile specifies
> where the
> process ID is dumped by beakerd and is setup while creating the
> DaemonContext object
> as follows and ExecStart specifies the location to the binary that is to
> be started."
>
>
> [1] http://git.beaker-project.org/cgit/beaker/plain/beaker.spec?h=develop
> [2] http://stackoverflow.com/a/17848250
> [3]
> http://echorand.me/2013/08/02/notes-on-writing-systemd-unit-files-for-beakers-daemon-processes/
>
> Hope those give you some ideas and point you towards the right direction.
>
> Best,
> Amit.
>
> --
> Amit Saha <http://echorand.me>
>
>
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