How to Increase the Swap Size on OpenBSD

To increase the size of the swap on my OpenBSD Virtual Private Server with the help of a swap file, I used the following commands:

# create file and set permissions
doas dd if=/dev/zero of=/home/swapfile bs=1m count=512
doas chmod 600 /home/swapfile
# activate swap (swapon)
doas swapctl -a /home/swapfile
# make permanent
echo '/home/swapfile none swap sw' | doas tee -a /etc/fstab

I used the /home partition for the swap file, since it was the one with the most free disk space on my tiny VPS.

The new amount of 768MB is available without a reboot and can be verified using e.g. swapctl or top.

$ swapctl -lk
Device         1K-blocks     Used    Avail Capacity  Priority
/dev/sd0b         262144    13488   248656     5%    0
/home/swapfile    524288    13956   510332     3%    0
Total             786432    27444   758988     3%

/dev/sd0b is the 256 MB swap that was automatically set up during installation (sticking mostly to defaults).

It does not hurt to verify the line landed in fstab.

$ tail -1 /etc/fstab
/home/swapfile none swap sw

Optionally one might reboot the machine and verify the expected swap size.