Upstart

Since I’m struggling with upstart, the ubuntu init replacement, I’m writing down some notes.

When you run start, status and stop commands on a daemon you’re actually running initctl {command}. You can see the available commands by running initctl help.

Most Ubuntu installations maintain the older /etc/init.d scripts for compatibility. You run those scripts with the traditional /etc/init.d/service_name {start|stop}. If you take a look at the /usr/sbin/service script you might notice that it contains the logic to check whether the script if configured in /etc/init or /etc/init.d and behaves according to that.

Some definitions

Upstart makes a difference between tasks and services. A task is a short-running process, while a service is a process that should keep running.

A job is defined in a /etc/init/<jobname>.conf configuration file.

Upstart also defines events and hooks, but for the time being we don’t care about them.

Configuration syntax

There are a few directives:

Easy ones

# this is a comment
author "Author name"
description "Description of the job"

console

console <log|none|output|owner>

Attaches stdin, stdout, and stderr as requested:

log: only used by system logs. Uses /var/log/upstart/* as stdout
none: /dev/null for everything
output: uses the console device (what does it mean?)
owner: similar to output

chdir / chroot

chdir /var/mydirectory
chroot /var/mydirectory

Runs the process with the specified working directory or in a chrooted jail rather than /.

exec

exec COMMAND [ARGS] ...

Single-line command to run

expect

expect <fork|daemon|stop>

This is the most dreaded configuration line. This tells upstart how the process will behave fork-wise. If the process doesn’t fork then don’t use this directive. If it forks once then use fork; if twice then daemon.

respawn

respawn

If enabled, the process will be restarted when its goal was changed to stop.

respawn limit COUNT INTERVAL

With this directive the job will be stopped if it is respawned more than COUNT times in INTERVAL seconds.

setgid / setuid

Sets the process user and group. Works with Upstart v1.4, mind you!

start

start on runlevel [2345]

Many syntaxes are allowed here. You can also hook the start to an external event:

start on started mysql

stop

Similar to start.

Reminders

Runlevels

You should know this, but..

0: system halt
1: single user mode
2: multi-user + networking (default)
3-5: same as 2 but not used
6: system reboot