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Add more information for booting read-only snapshots on Dracut distros (#431)

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Adapted from https://github.com/Antynea/grub-btrfs/issues/399#issuecomment-4478211233
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kennethso168
2026-05-23 16:55:09 +08:00
committed by GitHub
parent aeda46c2a0
commit fe2028b623
1 changed files with 33 additions and 2 deletions
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initramfs/readme.md
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@@ -40,8 +40,39 @@ Re-generate your initramfs
`mkinitcpio -P` (option -P means, all preset present in `/etc/mkinitcpio.d`)
#### Dracut based distros
Distributions that use Dracut to make their initramfs (many of the Fedora based Distros) simply have to pass either `rd.live.overlay.readonly=1` (to boot into the snapshot read only) or `rd.live.overlay.overlayfs=1` (to act like a livedisk, that is files can be changed but changes will be lost on the next boot) to their kernel command line in grub.
Grub-btrfs provides the variable `GRUB_BTRFS_SNAPSHOT_KERNEL_PARAMETERS` to add any command to the kernel command line. Set it to `GRUB_BTRFS_SNAPSHOT_KERNEL_PARAMETERS="rd.live.overlay.overlayfs=1"` to make snapshots immutable when booted into.
Distributions that use Dracut to make their initramfs (many of the Fedora based Distros) have to include the `overlayfs` module into the initramfs and pass either `rd.live.overlay.readonly=1` (to boot into the snapshot read only) or `rd.live.overlay.overlayfs=1` (to act like a livedisk, that is files can be changed but changes will be lost on the next boot) to their kernel command line in grub.
1. Include `overlayfs` module into dracut
```bash
echo 'add_dracutmodules+=" overlayfs "' | sudo tee /etc/dracut.conf.d/overlayfs.conf
```
2. Fix for dracut <109
Unfortunately, dracut version <109 has a bug that prevents overlayfs mount from properly working. [A fix has been commited into dracut version 109](https://github.com/dracut-ng/dracut-ng/commit/deeb670c28d12a478bbea95e29677e436d1912fb). If you are still on version < 109, instead of editing `/usr/lib/dracut/modules.d/70overlayfs/mount-overlayfs.sh` directly on your system, which will get overwritten on updates to the dracut package, we can duplicate the whole module with a lower priority number and carry out the patch there. As explained in this [very old notes about dracut](https://wwoods.fedorapeople.org/doc/dracut-notes.html):
> dracut refuses to overwrite files when installing things into the initramfs, so things installed by the the lower numbered modules have priority over the higher ones.
```bash
sudo cp -r /usr/lib/dracut/modules.d/70overlayfs /usr/lib/dracut/modules.d/69overlayfs
sudoedit /usr/lib/dracut/modules.d/69overlayfs/mount-overlayfs.sh
```
Edit the file as per [the commit](https://github.com/dracut-ng/dracut/commit/deeb670c28d12a478bbea95e29677e436d1912fb)
3. Regenerate the initramfs
```
# for current kernel's initramfs
sudo dracut -f
# for all kernels
sudo dracut -f --regenerate-all
```
4. Add kernel parameter and regenerate grub snapshot-submenu
Grub-btrfs provides the variable `GRUB_BTRFS_SNAPSHOT_KERNEL_PARAMETERS` in `/etc/default/grub-btrfs/config` to add any command to the kernel command line. Set it to `GRUB_BTRFS_SNAPSHOT_KERNEL_PARAMETERS="rd.live.overlay.overlayfs=1"` to make snapshots immutable when booted into.
After changing this run `sudo /etc/grub.d/41_snapshots-btrfs` to generate a new snapshot-submenu with the parameter added.
#### Other distribution