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Basic setup

  1. Install zfs-dracut
  2. Set mountpoint=/ for your root dataset (for compatibility, legacy also works, but is not recommended for new installations):
    zfs set mountpoint=/ pool/dataset
  3. Either (a) set bootfs= on the pool to the dataset:
    zpool set bootfs=pool/dataset pool
  4. Or (b) append root=zfs:pool/dataset to your kernel cmdline.
  5. Re-generate your initrd and update it in your boot bundle

Encrypted datasets have keys loaded automatically or prompted for.

If the root dataset contains children with mountpoint=s of /etc, /bin, /lib*, or /usr, they're mounted too.

For complete documentation, see dracut.zfs(7).

cmdline

  1. root= Root dataset is…
    (empty) the first bootfs= after zpool import -aN
    zfs:AUTO, zfs:, zfs (as above, but overriding other autoselection methods)
    ZFS=pool/dataset pool/dataset
    zfs:pool/dataset (as above)

    All +es are replaced with spaces (i.e. to boot from root pool/data set, pass root=zfs:root+pool/data+set).

    The dataset can be at any depth, including being the pool's root dataset (i.e. root=zfs:pool).

    rootfstype=zfs is equivalent to root=zfs:AUTO, rootfstype=zfs root=pool/dataset is equivalent to root=zfs:pool/dataset.

  2. spl_hostid: passed to zgenhostid -f, useful to override the /etc/hostid file baked into the initrd.

  3. bootfs.snapshot, bootfs.snapshot=snapshot-name: enables zfs-snapshot-bootfs.service, which creates a snapshot $root_dataset@$(uname -r) (or, in the second form, $root_dataset@snapshot-name) after pool import but before the rootfs is mounted. Failure to create the snapshot is noted, but booting continues.

  4. bootfs.rollback, bootfs.rollback=snapshot-name: enables zfs-snapshot-bootfs.service, which -Rf rolls back to $root_dataset@$(uname -r) (or, in the second form, $root_dataset@snapshot-name) after pool import but before the rootfs is mounted. Failure to roll back will fall down to the rescue shell. This has obvious potential for data loss: make sure your persistent data is not below the rootfs and you don't care about any intermediate snapshots.

  5. If both bootfs.snapshot and bootfs.rollback are set, bootfs.rollback is ordered after bootfs.snapshot.

  6. zfs_force, zfs.force, zfsforce: add -f to all zpool import invocations. May be useful. Use with caution.