If you haven’t installed a new version of Linux lately, you might be in for a shock. There is no /etc/inittab configuration file in Ubuntu releases. Upstart, the replacement for the System V init program, is designed to meet the demands of the latest plug-and-play hotplug environments. During the boot process, Upstart is especially helpful with filesystems mounted on portable and network devices.
Upstart Service Scripts
Pay particular attention to the scripts in the /etc/event.d directory. Future Linux releases might see service scripts currently in the /etc/init.d directory move there to become a part of the Upstart system. One service script, the logging daemon, logd, was already moved there for the Hardy Heron release. The configuration file, /etc/event.d/logd, is straightforward. First, logging is stopped in runlevels 0, 1, and 6 with commands like this:
stop on runlevel 0
Next, log output, unless otherwise configured, is sent to the console:
The /sbin/logd daemon is run by default. If it is stopped for any reason, it is restarted, as depicted by the respawn directive:
Upstart Scripts Replace /etc/inittab
If you remember the directives in the /etc/inittab configuration file, you’ll recognize the contents of the other files in the /etc/event.d directory. As the hardware advantages of Upstart are essentially transparent to most users, this section focuses on how Upstart provides equivalent functionality to /etc/inittab. The first line in a standard /etc/inittab file specifies the default runlevel. To review, for Debian-based distributions including Ubuntu, the default runlevel as signified by the
following directive is 2:
The default runlevel is now configured with Upstart’s rc-default configuration file in the /etc/event.d directory. In essence, the script takes the default runlevel from /etc/inittab if the file exists and a directive like id:2:initdefault is included; otherwise, it’s configured to set a runlevel of 2. Next, some scripts are run independent of runlevel, as configured by the following:
This effectively runs all scripts in the /etc/rcS.d directory. These are all “start” scripts, as they start with a capital S. In other words, they’re started whenever Linux is booted. The same scripts are run through Upstart, courtesy of the /etc/event.d/rcS script. The next directive from my old /etc/inittab specifies what needs to be done when Linux is booted into single-user mode, as specified by the recovery mode option described earlier in the GRUB configuration file. The S runlevel is synonymous with the single that appears in the GRUB configuration file, which starts single-user mode. The wait directive stays in the noted runlevel. The sulogin command, when invoked by the recovery mode option, boots and logs into the root account.
The equivalent Upstart functionality is available from the /etc/event.d/rcS-sulogin file, which invokes the sulogin command unless /etc/inittab exists on the system. These directives from /etc/inittab provide options; only one is run, based on the specified runlevel. For example, if the default runlevel is 2, the associated command runs the scripts in the /etc/rc2.d directory:
The equivalent Upstart script for runlevel 2 is /etc/event.d/rc2, which confirms the desired runlevel and then runs the following command:
exec /etc/init.d/rc 2
Linux systems are configured to accept the CTRL-ALT-DELETE key combination often associated with Microsoft systems. When the associated signal is received, the /etc/inittab file specifies the following directive, which starts the shutdown command in one second (-t1), limited by any existing rules specified in an /etc/shutdown.allow file (-a), if it exists, and reboots now (-r now).
ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now
In contrast, Upstart’s /etc/event.d/control-alt-delete file executes the following command, with fewer limitations. Of course, the command can be modified to suit your needs.
exec /sbin/shutdown -r now “Control-Alt-Delete pressed”
Many server systems are protected by Uninterruptable Power Supplies (UPS). When connected to a Linux system, they can send one of three signals to the system, which was interpreted by /etc/inittab with the following commands:
These options require the powstatd package, also known as the Configurable UPS Monitoring Daemon. It depends on the noted /etc/init.d/powerfail script as well as the /etc/ powstatd.conf configuration file. But as /sbin/powstatd is now a regular daemon controlled by the complementary /etc/init.d/powstatd script, it’s technically not part of Upstart. Linux systems typically include six consoles, also known as gettys. In /etc/inittab, they’re started with the following directives, where all six gettys are made available in runlevels 2 and 3.
1:2345:respawn:/sbin/getty 38400 tty1
2:23:respawn:/sbin/getty 38400 tty2
3:23:respawn:/sbin/getty 38400 tty3
4:23:respawn:/sbin/getty 38400 tty4
5:23:respawn:/sbin/getty 38400 tty5
6:23:respawn:/sbin/getty 38400 tty6
In the Upstart system, each of these gettys are started with ttyx files in the /etc/ event.d directory, where x represents the terminal number. While these files are more descriptive, they contain the same information. All six terminals are started in runlevels 2 and 3. When a user logs out of a terminal, the respawn directive regenerates that terminal with a new login screen. Communication in a text screen is plenty fast at 38400 bits per second.