BTRFS - enable hibernation

For a number of reasons that I don’t explain, I changed my distribution and opted to use Arch Linux on a BTRFS partition. This choice allows me to have change snapshots in addition to backups. I make it short: I had the need to enable hibernation because I find it very useful especially on a laptop. Often I have to stop work and prefer to find everything as it was before my return. The documentation exists and I consider it dispersive. For this I will limit myself to write small notes for the achievement of the purpose. This is not a how-to!

Subvolumes

I created the following subvolumes in the partition: @, @home, @swap, @cache, @log

NOTE: This procedure requires the creation of a dedicated sub-volume for swaps.

if it is not present you can easily create it with the next command Subvolumes.1 otherwise drop the command

Subvolumes.1

~# btrfs subvolume create /swap

Tip: Consider creating the subvolume directly below the top-level subvolume, e.g. @swap. Then, make sure the subvolume is mounted to /swap (or any other accessible location).

Generate the swapfile

~# pacman -S btrfs-progs
~# btrfs filesystem mkswapfile --size <your ram size>G --uuid clear /swap/swapfile

NOTE: To make hibernation work you need to ensure that the swapfile space is equal to your RAM size.

Activate the swapfile:

~# swapon /swap/swapfile

now you can check that it is up and running. Later you can add the config to fstab to make the change permanent!

~ 
❯ free -h
               total        used        free      shared  buff/cache   available
Mem:            31Gi       2,8Gi        25Gi       564Mi       3,7Gi        28Gi
Swap:           35Gi          0B        35Gi

Fstab - permanent mount

~# echo "/swap/swapfile none swap defaults 0 0" | tee -a /etc/fstab

the result will be similar to the following

~ 
❯ cat /etc/fstab
# Static information about the filesystems.
# See fstab(5) for details.

# <file system> <dir> <type> <options> <dump> <pass>
# /dev/nvme0n1p6
UUID=47e97784-1585-46ff-ba9b-e07ec8173824	/         	btrfs     	rw,relatime,ssd,discard=async,space_cache=v2,subvol=/@	0 0

# /dev/nvme0n1p6
UUID=47e97784-1585-46ff-ba9b-e07ec8173824	/home     	btrfs     	rw,relatime,ssd,discard=async,space_cache=v2,subvol=/@home	0 0

# /dev/nvme0n1p6
UUID=47e97784-1585-46ff-ba9b-e07ec8173824	/swap     	btrfs     	rw,relatime,ssd,discard=async,space_cache=v2,subvol=/@swap	0 0

# /dev/nvme0n1p6
UUID=47e97784-1585-46ff-ba9b-e07ec8173824	/var/cache	btrfs     	rw,relatime,ssd,discard=async,space_cache=v2,subvol=/@cache	0 0

# /dev/nvme0n1p6
UUID=47e97784-1585-46ff-ba9b-e07ec8173824	/var/log  	btrfs     	rw,relatime,ssd,discard=async,space_cache=v2,subvol=/@log	0 0

/swap/swapfile none swap defaults 0 0

it’s time for REBOOT!

Edit mkinitcpio.conf

~# sed -i 's/\(filesystems\)/\1 resume/' /etc/mkinitcpio.conf

NOTE: the command will add the resume parameter to the HOOKS list. Make sure it looks like the following example.

~ 
❯ cat /etc/mkinitcpio.conf | grep "HOOKS=" | tail -n 1      
HOOKS=(base udev autodetect microcode modconf kms keyboard keymap consolefont block filesystems resume fsck grub-btrfs-overlayfs)

If everything has worked properly so far, the last two parameters are missing. I refer to the UUID of the root partition and resume_offset referring to the swapfile. These parameters will be added in grub to allow the kernel to restore at boot time. Let’s move them!

UUID - root

~ 
❯ df -h | grep "/$"
/dev/nvme0n1p6  440G   73G    367G  17% /

NOTE: is an example of my use case. Your partition will be mapped to the correct device, otherwise, worry about checking which is the root partition.

~ 
❯ blkid -o value /dev/nvme0n1p6 | head -n1 
47e97784-1585-46ff-ba9b-e07ec8173824

UUID=47e97784-1585-46ff-ba9b-e07ec8173824

resume_offset - swapfile

~ 
❯  sudo btrfs inspect-internal map-swapfile -r /swap/swapfile

[sudo] password di ax: 
12952736

resume_offset=12952736

Edit /etc/default/grub

Open /etc/default/grub with vim and append resume=UUID= resume_offset= to the kernel arguments in the string "GRUB_CMDLINE_LINUX_DEFAULT=". The result will be as follows:

~ 
❯ cat /etc/default/grub | grep "GRUB_CMDLINE_LINUX_DEFAULT="
GRUB_CMDLINE_LINUX_DEFAULT="resume=UUID=47e97784-1585-46ff-ba9b-e07ec8173824 resume_offset=12952736 loglevel=3 quiet"

All that remains is to reload the grub configuration with the correct parameters:

~ 
❯ sudo grub-mkconfig -o /boot/grub/grub.cfg 

That’s it!

(END)