Provided by: zfs-dracut_2.2.6-1ubuntu2_amd64 
NAME
dracut.zfs — overview of ZFS dracut hooks
SYNOPSIS
parse-zfs.sh → dracut-cmdline.service
| ↓
| …
| ↓
\————————→ dracut-initqueue.service
| zfs-import-opts.sh
zfs-load-module.service ↓ | |
| | sysinit.target ↓ |
↓ | | zfs-import-scan.service ↓
zfs-import-scan.service ↓ ↓ | zfs-import-cache.service
| zfs-import-cache.service basic.target | |
\__________________| | ↓ ↓
↓ | zfs-load-key.sh
zfs-env-bootfs.service | |
↓ ↓ ↓
zfs-import.target → dracut-pre-mount.service
| ↑ |
| dracut-zfs-generator |
| _____________________/|
|/ ↓
| sysroot.mount ←——— dracut-zfs-generator
| |
| ↓
| initrd-root-fs.target ←— zfs-nonroot-necessities.service
| | |
| ↓ |
↓ dracut-mount.service |
zfs-snapshot-bootfs.service | |
| ↓ |
↓ … |
zfs-rollback-bootfs.service | |
| ↓ |
| /sysroot/{usr,etc,lib,&c.} ←———————————————————/
| |
| ↓
| initrd-fs.target
\______________________ |
\|
↓
export-zfs.sh initrd.target
| |
↓ ↓
dracut-shutdown.service …
|
↓
zfs-needshutdown.sh → initrd-cleanup.service
Compare dracut.bootup(7) for the full flowchart.
DESCRIPTION
Under dracut, booting with ZFS-on-/ is facilitated by a number of hooks in the 90zfs module.
Booting into a ZFS dataset requires mountpoint=/ to be set on the dataset containing the
root filesystem (henceforth "the boot dataset") and at the very least either the bootfs
property to be set to that dataset, or the root= kernel cmdline (or dracut drop-in) argument
to specify it.
All children of the boot dataset with canmount=on with mountpoints matching /etc, /bin,
/lib, /lib??, /libx32, and /usr globs are deemed essential and will be mounted as well.
zfs-mount-generator(8) is recommended for proper functioning of the system afterward
(correct mount properties, remounting, &c.).
CMDLINE
Standard
root=zfs:dataset, root=ZFS=dataset Use dataset as the boot dataset. All pluses
(‘+’) are replaced with spaces (‘ ’).
root=zfs:AUTO, root=zfs:, root=zfs, [root=] After import, search for the first pool with
the bootfs property set, use its value as-if
specified as the dataset above.
rootfstype=zfs root=dataset Equivalent to root=zfs:dataset.
rootfstype=zfs [root=] Equivalent to root=zfs:AUTO.
rootflags=flags Mount the boot dataset with -o flags; cf.
Temporary Mount Point Properties in
zfsprops(7). These properties will not last,
since all filesystems will be re-mounted from
the real root.
debug If specified, dracut-zfs-generator logs to the
journal.
Be careful about setting neither rootfstype=zfs nor root=zfs:dataset — other automatic boot
selection methods, like systemd-gpt-auto-generator and systemd-fstab-generator might take
precedent.
ZFS-specific
bootfs.snapshot[=snapshot-name] Execute zfs snapshot boot-dataset@snapshot-name before
pivoting to the real root. snapshot-name defaults to the
current kernel release.
bootfs.rollback[=snapshot-name] Execute zfs rollback -Rf boot-dataset@snapshot-name before
pivoting to the real root. snapshot-name defaults to the
current kernel release.
spl_hostid=host-id Use zgenhostid(8) to set the host ID to host-id; otherwise,
/etc/hostid inherited from the real root is used.
zfs_force, zfs.force, zfsforce Appends -f to all zpool import invocations; primarily
useful in conjunction with spl_hostid=, or if no host ID
was inherited.
FILES
parse-zfs.sh (cmdline)
Processes spl_hostid=. If root= matches a known pattern, above, provides /dev/root and
delays the initqueue until zfs(4) is loaded,
zfs-import-opts.sh (systemd environment generator)
Turns zfs_force, zfs.force, or zfsforce into ZPOOL_IMPORT_OPTS=-f for
zfs-import-scan.service or zfs-import-cache.service.
zfs-load-key.sh (pre-mount)
Loads encryption keys for the boot dataset and its essential descendants.
keylocation=prompt Is prompted for via
systemd-ask-password thrice.
keylocation=https://URL, keylocation=http://URL network-online.target is started
before loading.
keylocation=file://path If path doesn't exist, udevadm is
settled. If it still doesn't, it's
waited for for up to 10s.
zfs-env-bootfs.service (systemd service)
After pool import, sets BOOTFS= in the systemd environment to the first non-null bootfs
value in iteration order.
dracut-zfs-generator (systemd generator)
Generates sysroot.mount (using rootflags=, if any). If an explicit boot dataset was
specified, also generates essential mountpoints (sysroot-etc.mount, sysroot-bin.mount,
&c.), otherwise generates zfs-nonroot-necessities.service which mounts them explicitly
after /sysroot using BOOTFS=.
zfs-snapshot-bootfs.service, zfs-rollback-bootfs.service (systemd services)
Consume bootfs.snapshot and bootfs.rollback as described in CMDLINE. Use BOOTFS= if no
explicit boot dataset was specified.
zfs-needshutdown.sh (cleanup)
If any pools were imported, signals that shutdown hooks are required.
export-zfs.sh (shutdown)
Forcibly exports all pools.
/etc/hostid, /etc/zfs/zpool.cache, /etc/zfs/vdev_id.conf (regular files)
Included verbatim, hostonly.
mount-zfs.sh (mount)
Does nothing on systemd systems (if dracut-zfs-generator succeeded). Otherwise, loads
encryption key for the boot dataset from the console or via plymouth. It may not work at
all!
SEE ALSO
dracut.bootup(7), zfsprops(7), zpoolprops(7), dracut-shutdown.service(8),
systemd-fstab-generator(8), systemd-gpt-auto-generator(8), zfs-mount-generator(8),
zgenhostid(8)