Debian GNU Linux initrd documentation
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Supported boot parameters
- rollback=<on|yes|1> Do a rollback of specified snapshot.
- zfs_debug=<on|yes|1> Debug the initrd script
- zfs_force=<on|yes|1> Force importing the pool. Should not be necessary.
- zfs=<off|no|0> Don't try to import ANY pool, mount ANY filesystem or even load the module.
- rpool=<pool> Use this pool for root pool.
- bootfs=<pool>/<dataset> Use this dataset for root filesystem.
- root=<pool>/<dataset> Use this dataset for root filesystem.
- root=ZFS=<pool>/<dataset> Use this dataset for root filesystem.
- root=zfs:<pool>/<dataset> Use this dataset for root filesystem.
- root=zfs:AUTO Try to detect both pool and rootfs
In all these cases, <dataset> could also be <dataset>@<snapshot>.
The reason there are so many supported boot options to get the root filesystem, is that there are a lot of different ways too boot ZFS out there, and I wanted to make sure I supported them all.
Import using /dev/disk/by-*
The initrd will, if the variable
USE_DISK_BY_ID is set in the file
/etc/default/zfs, to import using the /dev/disk/by-* links. It will try to import in this order:
Import using cache file
If all of these imports fail (or if
USE_DISK_BY_ID is unset), it will then try to import using the cache file.
Last ditch attempt at importing
If that ALSO fails, it will try one more time, without any
Booting from snapshot:
Enter the snapshot for the
root= parameter like in this example:
linux /ROOT/debian-1@/boot/vmlinuz-3.2.0-4-amd64 root=ZFS=rpool/ROOT/debian-1@some_snapshot ro boot=zfs $bootfs quiet
This will clone the snapshot
rpool/ROOT/debian-1@some_snapshot into the filesystem
rpool/ROOT/debian-1_some_snapshot and use that as root filesystem. The original filesystem and snapshot is left alone in this case.
BEWARE that it will first destroy, blindingly, the
rpool/ROOT/debian-1_some_snapshot filesystem before trying to clone the snapshot into it again. So if you've booted from the same snapshot previously and done some changes in that root filesystem, they will be undone by the destruction of the filesystem.
0.6.4-1-3 it is now also possible to specify
rollback=1 to do a rollback of the snapshot instead of cloning it. BEWARE that this will destroy all snapshots done after the specified snapshot!
Select snapshot dynamically
0.6.4-1-3 it is now also possible to specify a NULL snapshot name (such as
root=rpool/ROOT/debian-1@) and if so, the initrd script will discover all snapshots below that filesystem (sans the at), and output a list of snapshot for the user to choose from.
Booting from native encrypted filesystem
Although there is currently no support for native encryption in ZFS On Linux, there is a patch floating around 'out there' and the initrd supports loading key and unlock such encrypted filesystem.
If there is separate filesystems (for example a separate dataset for each of
/var etc), the snapshot boot code will try to find the snapshot under each of these filesystems and clone (or rollback) each of these.
rpool/ROOT/debian-1@some_snapshot rpool/ROOT/debian-1/boot@some_snapshot rpool/ROOT/debian-1/usr@some_snapshot rpool/ROOT/debian-1/var@some_snapshot
These will create the following filesystems respectively (if not doing a rollback):
rpool/ROOT/debian-1_some_snapshot rpool/ROOT/debian-1/boot_some_snapshot rpool/ROOT/debian-1/usr_some_snapshot rpool/ROOT/debian-1/var_some_snapshot
The initrd code will use the
mountpoint option (if any) in the original (without the snapshot part) dataset to find where it should mount the dataset. Or it will use the name of the dataset below the root filesystem (
rpool/ROOT/debian-1 in this example) for the mount point.
Equal level filesystems
It is also possible to have all filesystems in the same 'level' as the root filesystems:
rpool/ROOT/root rpool/ROOT/boot rpool/ROOT/usr rpool/ROOT/var
This, however, require the setting of the
ZFS_INITRD_ADDITIONAL_DATASETS variable in the
/etc/default/zfs file. They are mounted in the order of appearance in this variable, so take care not to enter a child before it's mother.
This layout does however not allow for automatic snapshot cloning and mounting.
Also, here the
mountpoint property is required to know where to mount the dataset.
It does not matter (in both variants, decedent or equal filesystems if they're 'native' ZFS filesystems or legacy. The code will figure this out automatically. There is also no need for an entry in
/etc/fstab for these filesystems.