Ubuntu with Dracut, GRUB and RO snapshots - overlayfs

[Payne-X6]

#help-needed
My issue seems to be related to #214, but for some reason it is closed withou solution (??)

I have Ubuntu 25.10 intalled using debootstrap (not using standard installer).. Still, for me, everything seems to works just fine, but when change snapshot from grub, it's still in RO state...

I have add dracut module for overlayfs

/etc/dracut.conf.d/90-overlayfs.conf

add_dracutmodules+=" overlayfs "

and recompiled it.. Add kernel parameter for snapshots to GRUB-BTRFS config

/etc/default/grub-btrfs/config

GRUB_BTRFS_SNAPSHOT_KERNEL_PARAMETERS="rd.live.overlay.overlayfs=1"

and generated grub entries (seems right - with overlay settings from config file)...

But after "rollback", classic GNOME errors about gdm3, snapd, ... systemd service show up... I'm pretty sure it happens because it's RO, still...

I was trying to create btrfs subvolumes for /var/lib/gdm3, AccountsService (from Kali linux documentation), but it's getting out of hand really fast. now I need another subvol for snapd, and maybe others in the future... This does not look for me as an right path... I need overlayfs (or some alternative, I noticed that experiments with the systemd.volatile are not feasible)

[JMarcosHP]

If you are using snapper to manage your snapshots, then maybe your grub configuration is still pointing to an older RO snapshot

I published a guide that uses btrfs, snapper and grub-btrfs + a plugin for grub, this guide is for Debian users but you can adapt it for Ubuntu

here is

And yes, you are right. This is a disvantage of Debian itself, you need fine-grained subvolumes because the dpkg database is in /var, and making a whole subvolume to handle /var can leave your system inconsistent after each rollback, same with archlinux.

You can use timeshift, but again... the space used between snapshots goes crazy because it only relies on one subvolume for /

[Payne-X6]

Rather than a problem with the system settings, it looks like a Dracut issue. When I use initramfs-tools (with #250 or #359 scripts for initramfs), it works fine (boot into RO with overlayfs, then I create a RW copy and reboot there - exactly what I'm used to from Arch).

[Tom-0]

@Payne-X6 not sure is it going to help you in any wan now in Feb, but I am wrestling with the same in Fedora 43.
Apart from rd.live.overlay.overlayfs=1 I've added rd.debug and then I've spotted this in logs:

dracut-pre-pivot[563]: mount: /sysroot: fsconfig() failed: overlay: Unknown parameter 'subvol'.

This pointed me to this dracut commit: dracut-ng/dracut-ng@deeb670

... and that seems to address the problem for me :). Fix is in dracut 109 so since Nov. In Fedora there is no such new dracut version even in 'rawhide' so I've just manually removed $ROOTFLAGS for overlay mount options in /usr/lib/dracut/modules.d/90overlayfs/mount-overlayfs.sh, rebuilt initramfs and now I get this after booting from snapshot:

# mount|grep rootfsbase
LiveOS_rootfs on / type overlay (rw,relatime,seclabel,lowerdir=/run/rootfsbase,upperdir=/run/overlayfs,workdir=/run/ovlwork,uuid=on)
rootfs on /run/rootfsbase type rootfs (rw,seclabel)
/dev/mapper/luks-83dfac10-cade-4594-b47a-e4a77b49bd81 on /run/rootfsbase type btrfs (ro,relatime,seclabel,ssd,space_cache=v2,subvolid=302,subvol=/root/.snapshots/33/snapshot)
LiveOS_rootfs on /run/rootfsbase type overlay (rw,relatime,seclabel,lowerdir=/run/rootfsbase,upperdir=/run/overlayfs,workdir=/run/ovlwork,uuid=on)