Bsrgvty

A somewhat long-ish question this time: How can I ensure my PC uses the proper swapspace? I'm lucky enough to have an SSD disk where I have formatted a partition as Linux Swap. Problem is: it is not used.

This is what the system reports:

$ cat /proc/swaps
Filename Type Size Used Priority
/swapfile file 2097148 0 -2

If I turn on my swap partition,

$ sudo swapon /dev/sdb5

I get:

$ cat /proc/swaps
Filename Type Size Used Priority
/swapfile file 2097148 0 -2
/dev/sdb5 partition 16831484 0 -3

Then turning off the swapfile:

$ sudo swapoff /swapfile

$ cat /proc/swaps
Filename Type Size Used Priority
/dev/sdb5 partition 16831484 0 -2

This all works very well, but how can I make this stick also across a reboot?

I could add these commands to my .profile I guess, but I would like the system to use proper swap space also when someone else (potentially) logs in, i.e. as a system setting. Most likely I'll see a big improvement when the system is taxed... But how? I'd love to see the /swapfile gone, but I'm terrified I might end up with a system that won't boot :)

(As a sidenote - I know I should avoid using /dev/sdb5 and rather use the UUID – well, I'll get there eventually..!)

Unused swap is normal. For example here's my memory usage - this is my laptop and it's been up for 7 hours today while I'm working:

$ free -h
 total used free shared buff/cache available
Mem: 15Gi 3.2Gi 8.5Gi 1.5Gi 3.8Gi 10Gi
Swap: 979Mi 0B 979Mi

The fact is that you don't want to be actively using swap. Sometimes Linux will put unused programs in swap if there is enough memory pressure and that's fine. But if you are actually running out of memory you should really just add more RAM. Even if you are using an SSD swapping is slooow.

The only reason to add more swap is if you want to hibernate your machine. In that case you will need at least as much swap as you have RAM.

Anyway - if for some reason you are unable to add more RAM you need to put another line in your /etc/fstab for the new swap file. Something like this:

/dev/sdb5 none swap sw 0 0

It will now persist across reboots.

Side note:

If you want to see if your system is actively using swap use the dstat command and look at the paging column.

As it was pointed out by @Byte Commander, you have to edit the /etc/fstab file - this is what configures which file systems get mounted where, including swap.

All I had to do was to include the following line in my /etc/fstab file:

/dev/sdb5 none swap sw 0 0