On a headless server the short press of the power button should run a site-specific script that drains the machine before it halts. Which daemon receives that ACPI event from the kernel and runs a configured handler?
LPIC-1 Exam 101-500, objective 101. System architecture medium
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How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Correct acpid
Correct. acpid listens for ACPI events from the kernel and matches them against rules in /etc/acpi/events/, each naming a script to execute.
Not correct udevd
Wrong for this class of event. udev reacts to device uevents, adding and removing device nodes and applying rules from /etc/udev/rules.d/. A power button press is not a device appearing or disappearing.
Not correct systemd-logind
Wrong here, and the closest distractor. logind does act on the power key through HandlePowerKey in logind.conf, but that setting selects one of a fixed set of actions such as poweroff or suspend rather than running an arbitrary script.
Not correct cron
Wrong. cron starts jobs at times specified in crontabs. It has no connection to hardware events.
Why
ACPI is how firmware reports events such as a power or sleep button press, a lid closing or an AC adapter being unplugged. The kernel turns those into events that acpid reads and dispatches to shell scripts, which is what makes an arbitrary local response possible. On a desktop running systemd the power key is normally claimed by systemd-logind instead, so the two can conflict; where both are installed, acpid handles what logind has been configured to ignore.
Where this comes from
- Cited
- manual page acpid(8)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 101 and space the ones you get wrong.
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