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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 10:55:09 +02:00
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`) `mkinitcpio -P` (option -P means, all preset present in `/etc/mkinitcpio.d`)
#### Dracut based distros #### 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. 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.
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.
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. After changing this run `sudo /etc/grub.d/41_snapshots-btrfs` to generate a new snapshot-submenu with the parameter added.
#### Other distribution #### Other distribution