This dracut module fixes boot failures on older Ubuntu/OpenZFS systems (22.10 and earlier) when booting from initramfs images generated on newer systems (23.04 and later) with OpenZFS 2.2+.

OpenZFS 2.2.0 (released October 2023) introduced support for the casesensitive mount option, which corresponds to the casesensitivity ZFS dataset property that has existed since earlier versions. When dracut or systemd generators detect this property on a dataset, they automatically add casesensitive to the mount flags.

However, older versions of mount.zfs (OpenZFS 2.1.x and earlier) do not recognize casesensitive as a valid mount option and will fail with an "invalid option" error.

This problem manifests when:

1. ZFSBootMenu or initramfs is built on a system with OpenZFS 2.2+ (e.g., Ubuntu 24.04)
2. Target boot environment runs OpenZFS 2.1.x or earlier (e.g., Ubuntu 22.04, 22.10, 20.04, 18.04)
3. The dracut-generated initramfs includes casesensitive in the rootflags

During boot, the system will fail, unable to mount /sysroot.

The system drops to a dracut emergency shell. You can see the following in /run/initramfs/rdsosreport.txt :

mount[464]: filesystem 'pool/ROOT/dataset' cannot be mounted due to invalid option 'casesensitive'.
mount[464]: Use the '-s' option to ignore the bad mount option.

This module provides two complementary fixes that run during the initramfs boot sequence:

1. cmdline hook (priority 00): Removes casesensitive from /etc/cmdline.d/* files before they're processed
2. pre-mount hook (priority 00): Removes casesensitive from the generated /run/systemd/generator/sysroot.mount unit file before systemd attempts to mount it

Both hooks run early enough to intercept the problematic option before the mount attempt.

• Ubuntu 18.04 LTS (Bionic) - OpenZFS 0.7.x/0.8.x
• Ubuntu 20.04 LTS (Focal) - OpenZFS 0.8.x/2.0.x
• Ubuntu 22.04 LTS (Jammy) - OpenZFS 2.1.5
• Ubuntu 22.10 (Kinetic) - OpenZFS 2.1.5

• Ubuntu 23.04 (Lunar) and later - OpenZFS 2.2.x
• Ubuntu 24.04 LTS (Noble) and later - OpenZFS 2.2.x

1. Copy the module directory to your dracut modules directory:

sudo cp -r 95zfs-rootflags-fix /usr/lib/dracut/modules.d/

2. Ensure all scripts are executable:

sudo chmod +x /usr/lib/dracut/modules.d/95zfs-rootflags-fix/*.sh

3. Rebuild your initramfs with the module included:

sudo dracut -f --add zfs-rootflags-fix

Or to rebuild all kernel initramfs images:

sudo dracut -f --add zfs-rootflags-fix --regenerate-all

To automatically include this module in all future initramfs builds, create a dracut configuration file:

echo 'add_dracutmodules+=" zfs-rootflags-fix "' | sudo tee /etc/dracut.conf.d/zfs-rootflags-fix.conf

Then rebuild:

sudo dracut -f --regenerate-all

This module is safe to include on all systems, regardless of OpenZFS version:

• ✅ Safe on systems that don't have the casesensitive option (no-op)
• ✅ Safe on systems with OpenZFS 2.2+ that support the option (no-op)
• ✅ Safe when booting datasets that were created on the same system version
• ✅ Only makes changes when the problematic option is actually present

The module's sed commands only remove casesensitive if found; otherwise they do nothing. There's no performance impact and no risk of breaking working configurations.

95zfs-rootflags-fix/
├── module-setup.sh          # Dracut module configuration
├── zfs-fix-cmdline.sh       # Hook: fixes /etc/cmdline.d/* files (cmdline phase)
├── zfs-fix-rootflags.sh     # Hook: fixes sysroot.mount unit (pre-mount phase)
└── README.md                # This file

After booting a previously-failing dataset, you can verify the fix worked:

1. Check for the module's debug messages:

journalctl -b | grep "zfs-rootflags-fix"

2. Verify the system booted successfully (you should be at a normal prompt, not emergency shell)

3. Check that /sysroot was mounted:

mount | grep sysroot

This module is especially useful when using ZFSBootMenu to manage multiple boot environments across different Ubuntu versions. For example:

• ZFSBootMenu host: Ubuntu 24.04 (OpenZFS 2.2.x)
• Boot Environment 1: Ubuntu 24.04 (works fine)
• Boot Environment 2: Ubuntu 22.04 (needs this fix)
• Boot Environment 3: Ubuntu 20.04 (needs this fix)

With this module included in your ZFSBootMenu initramfs, all boot environments will work correctly regardless of their OpenZFS version.

You might think setting the ZFS property org.zfsbootmenu:rootflags on the dataset would override the flags. However, the casesensitive option can be added by:

1. dracut's cmdline module reading ZFS dataset properties
2. systemd generators during initramfs execution
3. Files in /etc/cmdline.d/ created during boot

These generation steps happen during boot in the initramfs, after the initramfs has already been created. The stored command line in the initramfs reflects the build-time system's ZFS version, which may include casesensitive.

Both hooks use priority 00 to run as early as possible:

• cmdline 00: Runs before cmdline processing
• pre-mount 00: Runs before any mounting, including /sysroot

This ensures the fix is applied before systemd attempts to use the problematic mount options.

If the module doesn't seem to run, verify it's included:

lsinitrd /boot/initrd.img-$(uname -r) | grep zfs-rootflags-fix

You should see the module's files listed.

If you still see mount errors:

1. Check that the hooks are executable in the initramfs
2. Verify the module is loaded: lsinitrd | grep zfs-rootflags-fix
3. Check journalctl output for hook execution messages
4. Ensure dracut was rebuilt after adding the module

This module is provided as-is for use with dracut and ZFS on Linux systems.

If you find issues or have improvements, please contribute back to help others facing this compatibility challenge in mixed OpenZFS environments.