A server has had swap areas added to it over several years. You need to see which of them the running kernel is actually paging to, and at what priority. Which command reports that?
LPIC-1 Exam 101-500, objective 104. Devices, Linux filesystems, filesystem hierarchy standard medium
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The options
Correct swapon --show
Correct. swapon --show prints a table of the swap areas currently in use, one row each, naming the device or file with its type, its size, how much of it is in use and its priority.
Not correct free -h
Wrong. free reports totals only: how much swap the system has altogether and how much of it is occupied. It never names the individual areas, so it cannot say which of them is active.
Not correct blkid -t TYPE=swap
Wrong. blkid reads the signatures written on block devices, so it finds every partition mkswap has ever prepared, activated or not. A signature on disk is not an area the kernel is using.
Not correct df -h
Wrong. df lists mounted filesystems and their free space. Swap is never mounted into the directory tree and holds no files, so it does not appear in df's output at all.
Why
Swap is set up in two steps and inspected in a third: mkswap writes the signature, swapon activates the area, and swapon --show lists what is active. The older spelling swapon -s does the same job in a fixed format, and its manual page calls it equivalent to `cat /proc/swaps` and deprecated in favour of --show; reading /proc/swaps yourself is the same information straight from the kernel. Priority is worth knowing because it decides order of use: a higher number is used first, it is set with -p or with pri= in the fstab options field, and areas left without one get a negative priority assigned by the kernel.
Where this comes from
- Cited
- manual page swapon(8)
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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