Debiain Bookworm Root on ZFS Guide: unnecessary REMAKE_INITRD

[mattico]

@rlaager, I have the following issue with the Debian Bookworm Root on ZFS HOWTO:

The guide still recommends using REMAKE_INITRD like so: echo REMAKE_INITRD=yes > /etc/dkms/zfs.conf. I noticed when upgrading kernels a deprecation warning about REMAKE_INITRD and did some investigation. It appears that REMAKE_INITRD doesn't do anything, and hasn't for a while?

openzfs/zfs#12867
openzfs/zfs#12781
dell/dkms#164

I may be misunderstanding something but I think this instruction is no longer necessary and can be removed. Thank you for the guide!

[mattico]

I also saw this warning when running Debian 11 but I was using kernel and ZFS backports and those PRs are recent enough it may still be necessary in the bullseye guide. Not sure.

[rlaager]

So I looked at the git history. This was introduced in commit 417c2a5 with the message:

Debian: Set REMAKE_INITRD=yes

The initrd needs to be rebuilt after the ZFS modules are built.
Otherwise, the system can (will?) fail to boot.

Closes: openzfs/zfs#10355
Reported-by: Christian Garbs <mitch@cgarbs.de>
Signed-off-by: Richard Laager <rlaager@wiktel.com>

So that references openzfs/zfs#10355. That is also referenced by openzfs/zfs#15706 which is the same issue being discussed here. As noted there, I closed that one in favor of this one.

So it seems we should just remove the REMAKE_INITRD on current Debian?

@mmitch, do you have any experience with this on current Debian?

@Zocker1999NET, have you had a chance to do any more testing?

[mattico]

I did a bit more digging into this, wanting to be sure that removing /etc/dkms/zfs.conf won't cause issues for my systems. I'm no initramfs/dkms expert but here's what I found.

In older versions of dkms the install_module and do_install functions will remake initrd if REMAKE_INITRD=yes. In dkms versions v2.8.8 and later (ca. Oct 2021) initrd handling was removed entirely, with the only remaining thing being the deprecation warning. Reading between the lines, dkms removed initrd generation support as it wasn't used downstream because distros have their own systems for regenerating initrd.

In Debian, deb triggers are used to run update-initramfs when necessary in response to a package install. The OpenZFS upstream includes a triggers file for openzfs-zfs-dkms which calls update-initramfs. That file was imported from downstream Debian, where it was added in response to a bug report where update-initramfs was not called after a zfs package upgrade. They also had an MR into experimental which removes that triggers file saying:

The first removes the unnecessary zfs-initramfs.triggers file containing an update-initramfs trigger. dh_compat 12 is smart enough to figure out that trigger automatically. This resolves a lintian error.

So presumably there's some system in Debian which would automatically run update-initramfs when necessary even without that .triggers file. That change hasn't made it into master though.

I checked the behavior on my machine with /etc/dkms/zfs.conf removed:

• reinstalling zfs-initramfs causes update-initramfs to run
• reinstalling zfs-dkms causes update-initramfs to run, whether or not zfs-initramfs is installed

Summary

REMAKE_INITRD doesn't do anything as of dkms v2.8.8. Deb/dpkg triggers ensure that update-initramfs is run after zfs-dkms or zfs-initramfs are installed, so it is not necessary anyway.

[mmitch]

I've checked some of my systems running ZFS (currently all on Debian stable/Bookworm):
One still has REMAKE_INITRD=yes in /etc/dkms/zfs.conf from the workaround in openzfs/zfs#10355 set.
Two other systems don't have it set.

I have not had any boot problems in the last years on any system regardless of the presence of the workaround.
So it looks to me like everything is fixed.

Looking at openzfs/zfs#10355 again, I think the crucial point was that /usr/src/zfs-0.8.3/dkms.conf contained the line REMAKE_INITRD="no" to explicitly disable the initrd rebuild. That created problems and had to be countered with REMAKE_INITRD=yes in /etc/dkms/zfs.conf.
Current ZFS versions don't contain that line any more (eg. in /usr/src/zfs-2.1.11/dkms.conf), so the regular Deb/dpkg triggers will rebuild the initrd like described in the previous comment.