What is the difference between the outputs of two commands, "free -m" and "cat /proc/sys/vm/swappiness," specifically in terms of swap

Question

Is there any difference between the outputs of two commands, "free -m" and "cat /proc/sys/vm/swappiness," specifically in terms of swap.

Answer 1

They’re rather different:

$ free -m
               total        used        free      shared  buff/cache   available
Mem:           31838       20657         595        5277       10585        5285
Swap:           8191        8191           0

$ cat /proc/sys/vm/swappiness
60

free -m shows how memory (and swap, if any) are currently used. cat /proc/sys/vm/swappiness shows the current value of the swappiness setting, which determines how the kernel balances page cache usage (part of the “buff/cache” output of free -m) and swap usage.

Changing swappiness will eventually affect the output of free -m: smaller values should result in lower swap usage (but won’t reduce existing swap usage) and lower cache usage, whereas higher values should result in higher swap usage and higher cache usage.

See Why does swappiness not work? and How does the kernel decide between disk-cache vs swap? for details of swappiness.