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Enable hibernation
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‎content/posts/2025-07-27-enable-hibernation.md‎

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date = '2025-07-27T11:51:54+02:00'
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draft = false
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title = 'Never return to a drained laptop again!'
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summary = 'Enable hibernation in Ubuntu 24.10'
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There have been several occasions where I haven't used my laptop in a few days, only to return to a
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completely drained battery. This is not only annoying, but also not very good for the battery.
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Maybe it's a false memory, but I want to recall that most OS's used to have a "Suspend, and then hibernate" feature. But now hibernation isn't even a default option in Ubuntu?
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This is a short guide on how to enable hibernation on Ubuntu 24.10.
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{{< alert >}}
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**Note:** I'm writing this in retrospect, and the instructions are probably not complete.
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This is mostly as a reminder to myself if I ever have to set it up again.
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{{</alert >}}
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## Setting it up
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### Resizing the swap file
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My system had a swap file (as opposed to a swap partition), but it was only 4GB in size (iirc). For
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hibernation purposes, it's recommended that your swap should be the size of your RAM, although
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there are ways to get
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[away with less](https://wiki.archlinux.org/title/Power_management/Suspend_and_hibernate#About_swap_partition/file_size).
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This command told me that my swap file was located at `/swap.img`.
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```bash
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swapon --show
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```
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To resize it, I did the following commands:
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```bash
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# Disable the swap file
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sudo swapoff -a
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# Remove the old swap file
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sudo rm /swap.img
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# Use `dd` to create a new 16GB file with zeroes
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sudo dd if=/dev/zero of=/swap.img count=16384 bs=1MiB
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# Set the correct permissions
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sudo chmod 600 /swap.img
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# Enable this file to be used as swap
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sudo swapon /swap.img
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```
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Instead of creating the file manually, it's also possible to use the command `mkswap`, which will
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set up the file with the correct permissions.
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Since I already had a swap file, it was already listed in `/etc/fstab` as:
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```bash
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/swap.img none swap sw 0 0
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```
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### Add kernel parameter to `grub`
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We need to pass `resume` and `resume_offset` as kernel parameters at boot.
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{{< alert >}}
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I'm not certain this is necessary. Newer `systemd` and `initramfs` will
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try to figure out where the resume data is. See `man initramfs-tools` and
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`man systemd-hibernate-resume`. But maybe when we are using a swap **file** rather than a
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partition, we need to where on a specific partition that file is?
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{{</alert>}}
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In `/etc/default/grub`, we add the `resume` parameter as the `UUID` of partition where the swap file lives. And `resume_offset` is where on that partition the file begins. (I think?)
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How do we find these values?
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The `UUID` we can find with the `findmnt` command:
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```bash
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sudo findmnt -no UUID -T /swap.img
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```
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And it should print the UUID. E.g.:
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```plaintext
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abcd1234-1234-1234-bdbd-asdfaaaabbbb
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```
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We find the offset with the `filefrag` command.
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```bash
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sudo filefrag -v /swap.img
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```
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```plaintext
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File size of /swap.img is 17179869184 (4194304 blocks of 4096 bytes)
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ext: logical_offset: physical_offset: length: expected: flags:
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0: 0.. 425983: [22118400..] 22544383: 425984:
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...
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```
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I've "highlighted" where the swap file starts, our offset, with square brackets, i.e. `22118400`.
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```bash
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GRUB_CMDLINE_LINUX_DEFAULT="<...> resume=UUID=<your uuid> resume_offset=<some offset>"
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```
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Example:
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```bash
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GRUB_CMDLINE_LINUX_DEFAULT="<...> resume=UUID=abcd1234-1234-1234-bdbd-asdfaaaabbbb resume_offset=1234"
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```
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And finally, to add this to your `grub` menu, run:
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```bash
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sudo update-grub
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```
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Then reboot to make it go into effect. After reboot, you can test it out by running:
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```bash
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systemctl hibernate
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```
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## Suspend, then hibernate
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I don't want my system to hibernate all the time, I just want it to hibernate if I don't use it for a while. Thankfully, [Chris Arderne](https://rdrn.me/ubuntu-hibernate-luks/#sleep-then-hibernate) has us covered.
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We can get this behavior by changing the `HandleLidSwitch` parameter in `/etc/systemd/logind.conf`:
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```plaintext
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[Login]
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HandleLidSwitch=suspend-then-hibernate
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```
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If the battery goes below 5%, the computer will hibernate. But we can also set it to hibernate based on time!
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In `/etc/systemd/sleep.conf` we can set the `HibernateDelaySec` paramter. I've set it to go into hibernation after 30 minutes.
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```plaintext
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[sleep]
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...
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HibernateDelaySec=1800
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```
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And then restart the logind service:
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```bash
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sudo systemctl restart systemd-logind.service
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```
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## Sources
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* [Arch Linux Wiki](https://wiki.archlinux.org/title/Power_management/Suspend_and_hibernate#Hibernation)
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* [Chris Arderne blog](https://rdrn.me/ubuntu-hibernate-luks/)
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* `man systemd-sleep.conf`
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* `man logind.conf`

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