I want to have a process which will be restarted if it crashes. I googled a bit and found that an easy solution is to use daemontools.
I didn't understand how to configure it.
It seems you're looking for a functionality already provided in Ubuntu with Upstart. The respawn stanza in the configuration will do exactly what you need. I would recommend against the use of a less standard way of dealing with this.
Without more details about the process you're trying to manage with it, it's hard to say what the configuration should look like. It depends on whether it forks and puts itself in the background for example. The Upstart documentation on the respawn stanza should give you more information.
Unfortunately, it's not yet possible to run User Jobs properly: cannot get upstart to run user job
Let's assume we want to keep the Calculator app running, even when it's being killed with fire (signal 9).
Create a configuration file in /etc/init/calculator.conf (based on this article):
#!upstart
description "Calculator"
# Start job via the daemon control script. Replace "gert" with your username.
exec su -l gert -c 'export DISPLAY=:0; /usr/bin/gnome-calculator'
# Restart the process if it dies with a signal
# or exit code not given by the 'normal exit' stanza.
respawn
# Give up if restart occurs 10 times in 90 seconds.
respawn limit 10 90
Start it by running
sudo start calculator
It opens on your current display (:0) and enjoy the awesomeness by seeing it restarting after closing it.
Identify the process ID, e.g. by doing ps aux | grep calculator:
gert 13695 0.2 0.4 349744 16460 ? Sl 13:38 0:00 /usr/bin/gnome-calculator
Kill it with fire.
sudo kill -9 13695
Watch it reappearing:
gert 16059 4.6 0.4 349736 16448 ? Sl 13:40 0:00 /usr/bin/gnome-calculator
Note that this will be more elegant with the plans for the Ubuntu 13.04 plans with proper User Job support.
