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December 16, 2012

Ubuntu 12.10: Minidlna on Boot

A big hat tip to Asaf Shahar for this one.

I recently upgraded to Ubuntu 12.10 on my main desktop machine from scratch, which means a number of things which had been installed and configured need to be re-done. One of those things is minidlna, a lightweight DLNA server.

If you don’t know, DLNA is a protocol for sharing media to devices. In my case, I use it to stream music, video and pictures from my desktop to my Blu-Ray player. It’s not perfect, at least in that the interface on the Blu-Ray player leaves much to be desired, but it works.

Minidlna does not come standard with Ubuntu, but it is in the repositories and installation is as easy as sudo apt-get install minidlna. Afterwards you configure /etc/minidlna.conf and you are good to go. The comments inside /etc/minidlna.conf are good enough that you won’t need further guidance from me here.

While all that was relatively painless, I soon discovered that minidlna was not starting on reboot. I checked the script in /etc/init.d and the symlinks in the various /etc/rc#.d/ directories and everything was correct. It started no problem by hand after boot using sudo service minidlna start. It was time to take the fight to google.

I quickly discovered a bug report that seemed appropriate. Apparently minidlna is attempting to start before networking is up and that causes it to error out. (If you have changed to Ubuntu 12.10 you may have noticed that networking does not start until after the login screen is displayed — a curious decision.)

If you have taken a look at the bug report, you’ll see a work-around posted by Asaf Shahar. He created a script using upstart to transform minidlna into a service managed by that tool.

I wasn’t quite convinced that was the answer for me, because that solution would skip whatever set up occurs in the /etc/init.d/minidlna script. At first I thought I could change his upstart script to simply invoke the minidlna script instead of the executable, but upstart was not created with that use in mind. (When creating an upstart service, upstart expects the executable to fork 1 or 2 times; a script will fork a great number of times and there is no way to tell upstart which process is actually the server process.)

The next natural solution would be to integrate the /etc/init.d/minidlna script into Shahar’s upstart script. But that would mean keeping the script up to date whenever the /etc/init.d/minidlna script changed. That’s not really something I want to have to do; after all I might even miss the fact that minidlna was updated. So another solution was needed.

In the process of researching upstart I discovered that one can use it for more than just servers. It can also execute a task (i.e. a short-lived process expected to finish on its own). I decided to have upstart run the minidlna script once the machine booted and networking was enabled. Now this is not perfect in that minidlna is still trying to start and failing on the normal boot process, but I can live with that.

To do this, create a file called /etc/init/start-minidlna.conf with the following contents:

# Task to start Minidlna - lightweight DLNA/UPNP media server
# Minidlna is not starting correctly on boot, see bug
# https://bugs.launchpad.net/ubuntu/+source/minidlna/+bug/1053173
#
description "Task to start minidlna"

start on (local-filesystems and net-device-up IFACE!=lo)

task

exec service minidlna start

That’s all there is to it. Now minidlna starts on boot. Once again I want to thank Asaf Shahar for his help.