Check if swap space exist in bash

Question

I want to check whether Swap space exist on a centos box in my bash script.Thus in cash there are no swap space on the server , then i can create swap.

I tried this approach

if [[ -n $(swapon -s) ]]; then
    :
else
   mkswap /dev/vda2 &> /dev/null
   swapon /dev/vda2
fi

Obviously it won't work since even when there is no swap swapon -s will return a string Filename Type Size Used Priority

See http://superuser.com/questions/727621/script-to-test-for-swap-then-exit-gracefully — mr.spuratic, Mar 14 '14 at 14:39
Related: https://unix.stackexchange.com/questions/23072/how-can-i-check-if-swap-is-active-from-the-command-line/537054 — Ciro Santilli OurBigBook.com, Aug 23 '19 at 13:56

score 10 · Answer 1 · answered Mar 14 '14 at 20:37

10

This works nicely for me:

if free | awk '/^Swap:/ {exit !$2}'; then
    echo "Have swap"
else
    echo "No swap"
fi

answered Mar 14 '14 at 20:37

Emmet

6,192
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score 1 · Answer 2 · answered Mar 14 '14 at 20:26

I don't see a means to do this just using 'swapon' since it: - always returns at least one line - always returns an error code of '0'

You could 'count lines' and if less then 2 then take the 'else' branch, i.e.

if [[ $(swapon -s | wc -l) -gt 1 ]] ; then echo "OK" ; else echo "Bad" ; fi

OK

if [[ $(swapon -s | wc -l) -gt 2 ]] ; then echo "OK" ; else echo "Bad" ; fi

Bad

Or simply check for 'devices' in the swapon output, i.e.:

if [[ $(swapon -s | grep -ci "/dev" ) -gt 0 ]] ;  then echo "OK" ; else echo "Bad" ; fi

Check if swap space exist in bash

2 Answers2