initramfs-tools reports "can't identify type of root filesystem" when label is missing

[Brett Holman]

When I attempt to regenerate an initramfs for a new root filsystem, update-initramfs is unable to identify the filesystem type of this initramfs.

```
# update-initramfs -u
update-initramfs: Generating /boot/initrd.img-5.15.0-1059-kvm
W: Couldn't identify type of root file system for fsck hook
W: mkconf: MD subsystem is not loaded, thus I cannot scan for arrays.
W: mdadm: failed to auto-generate temporary mdadm.conf file.
```

the mounted filesystem:
```
# cat /proc/mounts | grep xfs
/dev/sda1 / xfs rw,relatime,attr2,inode64,logbufs=8,logbsize=32k,noquota 0 0
```

fstab:
```
# cat /etc/fstab | grep xfs
LABEL=cloudimg-rootfs / xfs defaults 0 1
```

cmdline:
```
BOOT_IMAGE=/boot/vmlinuz-5.15.0-1059-kvm root=PARTUUID=575c9681-fb9d-457c-a3b5-407dda61a919 ro console=tty1 console=ttyS0 panic=-1
```

The failure is in hooks/fsck when it calls resolve_device(). The function returns 1 and echos nothing because it has a LABEL, not a UUID or PARTUUID.

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: initramfs-tools 0.140ubuntu13.4
ProcVersionSignature: Ubuntu 5.15.0-1059.64-kvm 5.15.149
Uname: Linux 5.15.0-1059-kvm x86_64
ApportVersion: 2.20.11-0ubuntu82.5
Architecture: amd64
CasperMD5CheckResult: unknown
Date: Wed Jun 5 01:25:29 2024
PackageArchitecture: all
ProcEnviron:
 TERM=vt220
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=C.UTF-8
 SHELL=/bin/bash
SourcePackage: initramfs-tools
UpgradeStatus: No upgrade log present (probably fresh install)

[Benjamin Drung (bdrung)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. I failed to reproduce the issue. I took a jammy VM and added a label to the boot device:

```
sudo tune2fs -L somelabel /dev/vda3
```

Configured fstab to look for the label:

```
$ grep -w / /etc/fstab | grep -v ^#
LABEL=somelabel / ext4 errors=remount-ro 0 1
```

and successfully updated the initrd:

```
$ sudo update-initramfs -u
update-initramfs: Generating /boot/initrd.img-6.5.0-35-generic
```

I checked the call from `resolve_device`:

```
$ blkid -l -t LABEL=somelabel -o device
/dev/vda3
```

Can you let mkinitramfs run with `set -x` to get some log messages?

[Brett Holman (holmanb)]

After digging in a little bit I noticed that this is just a case of a confusing error message. It turns out that the label was just missing from this filesystem. I'll update the bug title accordingly.

[Benjamin Drung (bdrung)]

Suggestion:

```
diff --git a/hooks/fsck b/hooks/fsck
index f6348e81..5e5b6aae 100755
--- a/hooks/fsck
+++ b/hooks/fsck
@@ -44,6 +44,7 @@ _read_fstab_entry () {
 # Find a specific fstab entry and print its type (if found, and pass != 0)
 # $1=mountpoint
 get_fsck_type_fstab () {
+ local device
        eval "$(_read_fstab_entry "$1")"

        # Not found by default.
@@ -51,9 +52,9 @@ get_fsck_type_fstab () {
                # Ignore filesystem type for /, as it is not available and
                # therefore never used at boot time
                if [ "${MNT_DIR}" = "/" ] || [ "${MNT_TYPE}" = "auto" ]; then
- MNT_FSNAME="$(resolve_device "${MNT_FSNAME}")"
- if ! get_fstype "${MNT_FSNAME}"; then
- echo "W: Couldn't identify type of $2 file system for fsck hook" >&2
+ device="$(resolve_device "${MNT_FSNAME}")"
+ if ! get_fstype "${device}"; then
+ echo "W: Couldn't identify type of $2 file system '$MNT_FSNAME' for fsck hook" >&2
                        fi
                else
                        echo "${MNT_TYPE}"
```

This would change the error message to:

```
$ sudo update-initramfs -u
update-initramfs: Generating /boot/initrd.img-6.8.0-22-generic
W: Couldn't identify type of root file system 'LABEL=foo' for fsck hook
```

[Brett Holman (holmanb)]

I haven't tested the diff, but this looks like an improvement to me. The new output message improves the messaging to the user with a clue that LABEL resolution is involved in fs type lookup and a possible source of the issue.

+1 thanks @bdrung

[Launchpad Janitor (janitor)]

This bug was fixed in the package initramfs-tools - 0.142ubuntu29

---------------
initramfs-tools (0.142ubuntu29) oracular; urgency=medium

  [ Jeffery To ]
  * Fix resume failure due to resume=UUID=... in certain cases (LP: #1769297)

  [ Benjamin Drung ]
  * resume: always write valid resume device to /sys/power/resume (LP: #1769297)
  * fsck: Mention file system name in failed identification warning
    (LP: #2068077)

 -- Benjamin Drung <email address hidden> Wed, 03 Jul 2024 13:55:55 +0200