An isolated machine has no network time source. Its battery-backed real-time clock is known to be right, but a script has left the running system clock hours adrift. Which command copies the hardware clock's time into the running system clock?
LPIC-1 Exam 102-500, objective 108. Essential system services medium
Machine-checked — no person has signed for it. This question was read against the source cited below by an automated pass, which found no contradiction. That is a weaker claim than it sounds: the same kind of process wrote the question, so it can confirm its own mistake.
Treat it as a good draft rather than as settled fact, and read the source below before you rely on it. It is not used in mock exams here — only questions a person has signed for are.
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 hwclock --hctosys
Correct. --hctosys (short form -s) reads the RTC and sets the system clock from it, applying the UTC-or-local interpretation recorded in /etc/adjtime.
Not correct hwclock --systohc
Wrong, and it makes things worse. --systohc (-w) writes the current system time into the RTC, so the known-good hardware clock would be overwritten with the wrong time.
Not correct hwclock --show
Wrong. --show (-r) only prints the RTC's time on standard output. It is the right way to check the hardware clock, but it changes nothing.
Not correct hwclock --systz
Wrong. --systz sets the kernel's notion of the timezone (and, on a local-time RTC, warps the system clock accordingly) without reading the RTC's time. It is used early in boot, not to correct a drifted system clock.
Why
The two directions are easy to mix up: hctosys means hardware clock to system clock, systohc means system clock to hardware clock. Read the option name as source-to-destination and the direction falls out. Only root may run either, because both change a clock the kernel owns.
Where this comes from
- Cited
- manual page hwclock(8)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 108 and space the ones you get wrong.
More questions on this objective
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- On a systemd host, type the single command that turns on automatic network time synchronisation (do not include a path). machine-checked