Which THREE of the following have been used on Linux as the init system, that is the first userspace process the kernel starts as PID 1?
LPIC-1 Exam 101-500, objective 101. System architecture medium
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The options
Choose 3.
Correct SysVinit
Correct. The traditional System V init reads /etc/inittab, uses numbered runlevels, and starts services through the shell scripts in /etc/init.d.
Correct Upstart
Correct. Upstart was an event-driven init used by Ubuntu and by Red Hat Enterprise Linux 6, configured with job files in /etc/init.
Not correct inittab
Wrong. /etc/inittab is the configuration file SysVinit reads, including its initdefault runlevel line. A configuration file cannot be PID 1.
Not correct runlevel
Wrong. runlevel is a small command that reports the previous and current runlevel. It is a reporting tool, not an init system.
Correct systemd
Correct. systemd is the init on most current distributions, managing units and targets and controlled with systemctl.
Why
All three appear in the LPIC-1 objectives because you may meet any of them: SysVinit with /etc/inittab and runlevels, Upstart with event-driven jobs under /etc/init, and systemd with units and targets. Whichever is in use, the kernel starts exactly one PID 1 and every other process descends from it. You can check which one is running with ps -p 1 -o comm=.
Where this comes from
- Cited
- LPI exam objective 101.2
- What it says
- Awareness of SysVinit, systemd and Upstart as the process the kernel starts first.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 101 and space the ones you get wrong.