95 lines
4.5 KiB
Markdown
95 lines
4.5 KiB
Markdown
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DESCRIPTION
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These scripts are intended to be used with initramfs-tools, which is a similar
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software product to "dracut" (which is used in RedHat based distributions),
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and is mainly used by Debian GNU/Linux and derivatives to create an initramfs
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so that the system can be booted off a ZFS filesystem. If you have no need or
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interest in this, then it can safely be ignored.
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These script were written with the primary intention of being portable and
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usable on as many systems as possible.
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This is, in practice, usually not possible. But the intention is there.
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And it is a good one.
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They have been tested successfully on:
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* Debian GNU/Linux Wheezy
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* Debian GNU/Linux Jessie
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It uses some functionality common with the SYSV init scripts, primarily
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the "/etc/zfs/zfs-functions" script.
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FUNCTIONALITY
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* Supports booting of a ZFS snapshot.
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Do this by cloning the snapshot into a dataset. If this, the resulting
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dataset, already exists, destroy it. Then mount it as the root filesystem.
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* If snapshot does not exist, use base dataset (the part before '@')
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as boot filesystem instead.
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* Clone with 'mountpoint=none' and 'canmount=noauto' - we mount manually
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and explicitly.
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* Allow rollback of snapshots instead of clone it and boot from the clone.
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* If no snapshot is specified on the 'root=' kernel command line, but
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there is an '@', then get a list of snapshots below that filesystem
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and ask the user which to use.
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* Support all currently used kernel command line arguments
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* Core options:
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All the different distributions have their own standard on what to specify
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on the kernel command line to boot of a ZFS filesystem.
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Supports the following kernel command line argument combinations
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(in this order - first match win):
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* rpool=<pool> (tries to finds bootfs automatically)
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* bootfs=<pool>/<dataset> (uses this for rpool - first part)
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* rpool=<pool> bootfs=<pool>/<dataset>
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* -B zfs-bootfs=<pool>/<fs> (uses this for rpool - first part)
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* rpool=rpool (default if none of the above is used)
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* root=<pool>/<dataset> (uses this for rpool - first part)
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* root=ZFS=<pool>/<dataset> (uses this for rpool - first part, without 'ZFS=')
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* root=zfs:AUTO (tries to detect both pool and rootfs
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* root=zfs:<pool>/<dataset> (uses this for rpool - first part, without 'zfs:')
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Option <dataset> could also be <snapshot>
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* Extra (control) options:
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* zfsdebug=(on,yes,1) Show extra debugging information
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* zfsforce=(on,yes,1) Force import the pool
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* rollback=(on,yes,1) Rollback (instead of clone) the snapshot
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* 'Smarter' way to import pools. Don't just try cache file or /dev.
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* Try to use /dev/disk/by-vdev (if /etc/zfs/vdev_id.conf exists),
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* Try /dev/mapper (to be able to use LUKS backed pools as well as
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multi-path devices).
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* /dev/disk/by-id and any other /dev/disk/by-* directory that may exist.
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* Use /dev as a last ditch attempt.
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* Fallback to using the cache file if that exist if nothing else worked.
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* Only try to import pool if it haven't already been imported
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* This will negate the need to force import a pool that have not been
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exported cleanly.
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* Support exclusion of pools to import by setting ZFS_POOL_EXCEPTIONS
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in /etc/default/zfs.
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Controlling in which order devices is searched for is controlled by
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ZPOOL_IMPORT_PATH variable set in /etc/defaults/zfs.
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* Support additional configuration variable ZFS_INITRD_ADDITIONAL_DATASETS
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to mount additional filesystems not located under your root dataset.
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For example, if the root fs is specified as 'rpool/ROOT/rootfs', it will
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automatically and without specific configuration mount any filesystems
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below this on the mount point specified in the 'mountpoint' property.
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Such as 'rpool/root/rootfs/var', 'rpool/root/rootfs/usr' etc)
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However, if one prefer to have separate filesystems, not located below
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the root fs (such as 'rpool/var', 'rpool/ROOT/opt' etc), special
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configuration needs to be done. This is what the variable, set in
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/etc/defaults/zfs file, needs to be configured. The 'mountpoint'
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property needs to be correct for this to work though.
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* Allows mounting a rootfs with mountpoint=legacy set.
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* Include /etc/modprobe.d/{zfs,spl}.conf in the initrd if it/they exist.
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* Include the udev rule to use by-vdev for pool imports.
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* Include the /etc/default/zfs file to the initrd.
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