You have just run `mkswap /dev/sdb2`. Which command makes the kernel start using that swap area immediately, without a reboot?
LPIC-1 Exam 101-500, objective 104. Devices, Linux filesystems, filesystem hierarchy standard easy
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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
Not correct free -h
Wrong. free only reports memory and swap usage. It is how you would confirm the new swap appeared, not how you enable it.
Not correct mount -t swap /dev/sdb2 /swap
Wrong. Swap is never mounted into the directory tree; it has no files and no mount point. The fstab entry for swap uses the mount point `none` or `swap` precisely because there is nothing to mount.
Not correct swapoff /dev/sdb2
Wrong, and the opposite. swapoff deactivates a swap area and pages its contents back into RAM.
Correct swapon /dev/sdb2
Correct. swapon activates a prepared swap area for the running kernel. `swapon -a` activates every swap entry listed in /etc/fstab instead.
Why
Swap setup is two steps: mkswap writes the swap signature and UUID onto the partition or file, then swapon tells the running kernel to use it. To make it survive a reboot you also add a line to /etc/fstab with type `swap` and option `defaults` or `sw`.
Where this comes from
- Cited
- LPI exam objective 104.1
- What it says
- Set up and use swap space with mkswap and swapon.
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 104 and space the ones you get wrong.
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