I recently migrated my system to NVMe drives (great decision, by the way), and part of my reason for doing so was much faster swap, for some outrageously memory-hungry finite element mesh generation stuff.

I also wanted to enlarge the swap. I use LVM on top of software RAID, and encrypted home directories on top of that, which means the Ubuntu automatically set up encrypted swap for me. I had a non-encrypted swap volume at:

/dev/vg0/swap

I didn’t have much luck finding information about how the cryptswap is set up by the installer, which is why I’m writing this. It turns out that the crypt swap is configured in /etc/crypttab, where I have a line like this:

cryptswap1 /dev/vg0/swap /dev/urandom swap,offset=1024,cipher=aes-xts-plain64

What this means is that the system will create a crypt device called /dev/mapper/cryptswap1 at boot using a random seed, on top of /dev/vg0/swap. It will then run mkswap and swapon on the encrypted device.

This latter part is specified in /etc/fstab like:

/dev/mapper/cryptswap1 none swap sw 0 0

So, if your base unencrypted swap partition is an LVM logical volume, all you have to do is use lvextend to make it larger and (the easiest way) reboot. On reboot the larger device will automatically be used in its entirety.