You corrected the running system's clock with `date -s`, but after the next power cycle the machine came back with the old wrong time. Which command copies the corrected system clock into the hardware (RTC) clock?
LPIC-1 Exam 102-500, objective 108. Essential system services 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 hwclock --systohc
Correct. --systohc (short form -w) writes the current system time into the hardware real-time clock, which is the clock the machine reads at the next boot.
Not correct hwclock --hctosys
Wrong, and the exact opposite direction. --hctosys (short form -s) sets the system clock from the hardware clock, which would restore the wrong time.
Not correct hwclock --show
Wrong. --show (short form -r) only reads and prints the hardware clock. It changes nothing.
Not correct hwclock --adjust
Wrong. --adjust applies the accumulated drift correction recorded in /etc/adjtime to the RTC. It compensates for the RTC's own inaccuracy; it does not copy the current system time into it.
Why
Linux keeps two clocks: the system clock maintained by the kernel, and the battery-backed hardware clock in the machine. date reads and writes only the system clock. hwclock bridges them: -w/--systohc pushes system to hardware, -s/--hctosys pulls hardware to system. On a systemd host, `timedatectl set-time` sets both at once, and enabling NTP synchronisation also causes the RTC to be updated periodically.
Where this comes from
- Cited
- LPI exam objective 108.1
- What it says
- Set the system date and time, and set the hardware clock to the correct time in UTC.
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
- On a systemd-based distribution, which file determines the local time zone used by the C library when formatting times? machine-checked
- A host runs chrony as its NTP client. Which command shows the list of time sources chrony is currently talking to and how it rates each one? machine-checked
- In /etc/ntp.conf you find the line `server 0.pool.ntp.org iburst`. What does the `iburst` keyword do? machine-checked
- A minimal systemd host synchronises its clock with systemd-timesyncd. Which statement about that service is accurate? machine-checked
- On a systemd host, type the single command that turns on automatic network time synchronisation (do not include a path). machine-checked
- You have just set the system clock correctly by hand and want the hardware clock to match, so the correction survives a reboot. Type the command, using its short option. machine-checked