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38 lines
1.8 KiB
Markdown
38 lines
1.8 KiB
Markdown
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# Hibernation
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Hibernation, also called **S4** sleeping or Suspend to disk, is the process of saving the machine's state into swap
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space, and completely powering off the machine. This means that there will be no power consumption until the next
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power on.
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This can be an extremely nice feature to have on laptops, allowing you to save the state at any point without
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worrying of running out of battery (like you might with regular Suspend / **S3** sleeping, which keeps the RAM
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powered on).
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To be able to hibernate, you will need to have a swap partition or file (although using a swap file could be
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problematic if you use encryption, so a swap partition is recommended), which should ideally be as big as your RAM
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(though even if your swsp is smaller than RAM, you still have a good chance of hibernating successfully).
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## Initramfs
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First thing we'll need to do is set up initramfs with support to restore the previous state after hibernation.
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- When using a busybox-based initramfs (with `udev` in your `HOOKS`), you will need to add a `resume` hook anywhere
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after `udev`.
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- With `systemd` based initramfs (you have `systemd` in your `HOOKS`), a resume mechanism is already provided, no
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need to add any extra hooks.
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## Kernel parameters
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To be able to resume from hibernation, you will need to let the kernel know where to resume from, that is, your swap
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partition. You can do that with the `resume` parameter, like this:
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- `resume=UUID=...`
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- `resume="PARTLABEL=Swap partition`
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- `resume=/dev/archVolumeGroup/archLogicalVolume`
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### Swap File
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If you'd like to use a swap file, set `resume` parameter to the partition on which your swap file lives, and set
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`resume_offset`, which you can find with `filefrag -v /path/to/swapfile` command. (When on btrfs, the `filefrag`
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command will not work, instead you should use `btrfs inspect-internal map-swapfile -r /path/to/swapfile`)
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