Setting up a Btrfs Swapfile with Hibernation Support on Ubuntu

Creating a swapfile on a Btrfs file system requires a few extra steps due to Copy-on-Write (COW) and fragmentation concerns. This guide walks you through setting up a swapfile with hibernation (resume) support.

1. Calculate Recommended Swap Size

SWAPSIZE=$(free | awk '/Mem/ {x=$2/1024/1024; printf "%.0fG", (x<2 ? 2*x : x<8 ? 1.5*x : x) }')

If RAM < 2GB → swap = 2 × RAM
If RAM < 8GB → swap = 1.5 × RAM
Otherwise → swap = RAM

2. Create a Dedicated Btrfs Subvolume

sudo btrfs subvolume create /swap

3. Disable Copy-on-Write (COW)

sudo chattr +C /swap

Note: Run this before creating the swapfile.

4. Create and Configure the Swapfile

sudo mkswap --file -L SWAPFILE --size $SWAPSIZE /swap/swapfile

sudo bash -c 'echo /swap/swapfile none swap defaults 0 0 >>/etc/fstab'

sudo swapon -av

5. Get the UUID of the Swap Partition

sudo findmnt /swap -o UUID

Take note of the UUID for the next step.

6. Find the `resume_offset` for Hibernation

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

Copy the returned resume_offset value.

7. Configure GRUB for Hibernation Support

Edit /etc/default/grub and add the following to GRUB_CMDLINE_LINUX_DEFAULT:

resume=UUID=XXXXXXXXXXXXXXXXXXXXXXXXXX resume_offset=XXXX

Replace XXXXXXXXXXXXXXXXXXXXXXXXXX with the UUID from step 5
Replace XXXX with the offset from step 6

sudo update-grub

8. Enable Hibernation in KDE Menu (Kubuntu)

To make the hibernate option appear in the KDE system menu, create the following file:

sudo nano /etc/polkit-1/rules.d/10-enable-hibernate.rules

Add this content:

polkit.addRule(function(action, subject) {
    if (action.id == "org.freedesktop.login1.hibernate" ||
        action.id == "org.freedesktop.login1.hibernate-multiple-sessions" ||
        action.id == "org.freedesktop.upower.hibernate" ||
        action.id == "org.freedesktop.login1.handle-hibernate-key" ||
        action.id == "org.freedesktop.login1.hibernate-ignore-inhibit")
    {
        return polkit.Result.YES;
    }
});

Save and reboot. The hibernate option should now be available in the KDE menu.