2022-04-04 23:14:49 +00:00
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.\" SPDX-License-Identifier: 0BSD
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.\"
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contrib: dracut: fix race with root=zfs:dset when necessities required
This had always worked in my testing, but a user on hardware reported
this to happen 100%, and I reproduced it once with cold VM host caches.
dracut-zfs-generator runs as a systemd generator, i.e. at Some
Relatively Early Time; if root= is a fixed dataset, it tries to
"solve [necessities] statically at generation time".
If by that point zfs-import.target hasn't popped (because the import is
taking a non-negligible amount of time for whatever reason), it'll see
no children for the root datase, and as such generate no mounts.
This has never had any right to work. No-one caught this earlier because
it's just that much more convenient to have root=zfs:AUTO, which orders
itself properly.
To fix this, always run zfs-nonroot-necessities.service;
this additionally simplifies the implementation by:
* making BOOTFS from zfs-env-bootfs.service be the real, canonical,
root dataset name, not just "whatever the first bootfs is",
and only set it if we're ZFS-booting
* zfs-{rollback,snapshot}-bootfs.service can use this instead of
re-implementing it
* having zfs-env-bootfs.service also set BOOTFSFLAGS
* this means the sysroot.mount drop-in can be fixed text
* zfs-nonroot-necessities.service can also be constant and always
enabled, because it's conditioned on BOOTFS being set
There is no longer any code generated at run-time
(the sysroot.mount drop-in is an unavoidable gratuitous cp).
The flow of BOOTFS{,FLAGS} from zfs-env-bootfs.service to sysroot.mount
is not noted explicitly in dracut.zfs(7), because (a) at some point it's
just visual noise and (b) it's already ordered via d-p-m.s from z-i.t.
Backport-of: 3399a30ee02d0d31ba2d43d0ce0a2fd90d5c575d
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
2023-03-28 20:49:50 +00:00
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.Dd March 28, 2023
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2022-04-04 23:14:49 +00:00
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.Dt DRACUT.ZFS 7
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.Os
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.
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.Sh NAME
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.Nm dracut.zfs
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.Nd overview of ZFS dracut hooks
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.
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.Sh SYNOPSIS
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.Bd -literal -compact
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parse-zfs.sh \(-> dracut-cmdline.service
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| \(da
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| …
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| \(da
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\e\(em\(em\(em\(em\(em\(em\(em\(em\(-> dracut-initqueue.service
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| zfs-import-opts.sh
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zfs-load-module.service \(da | |
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| | sysinit.target \(da |
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\(da | | zfs-import-scan.service \(da
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zfs-import-scan.service \(da \(da | zfs-import-cache.service
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| zfs-import-cache.service basic.target | |
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\e__________________| | \(da \(da
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\(da | zfs-load-key.sh
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zfs-env-bootfs.service | |
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\(da \(da \(da
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zfs-import.target \(-> dracut-pre-mount.service
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| \(ua |
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| dracut-zfs-generator |
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contrib: dracut: fix race with root=zfs:dset when necessities required
This had always worked in my testing, but a user on hardware reported
this to happen 100%, and I reproduced it once with cold VM host caches.
dracut-zfs-generator runs as a systemd generator, i.e. at Some
Relatively Early Time; if root= is a fixed dataset, it tries to
"solve [necessities] statically at generation time".
If by that point zfs-import.target hasn't popped (because the import is
taking a non-negligible amount of time for whatever reason), it'll see
no children for the root datase, and as such generate no mounts.
This has never had any right to work. No-one caught this earlier because
it's just that much more convenient to have root=zfs:AUTO, which orders
itself properly.
To fix this, always run zfs-nonroot-necessities.service;
this additionally simplifies the implementation by:
* making BOOTFS from zfs-env-bootfs.service be the real, canonical,
root dataset name, not just "whatever the first bootfs is",
and only set it if we're ZFS-booting
* zfs-{rollback,snapshot}-bootfs.service can use this instead of
re-implementing it
* having zfs-env-bootfs.service also set BOOTFSFLAGS
* this means the sysroot.mount drop-in can be fixed text
* zfs-nonroot-necessities.service can also be constant and always
enabled, because it's conditioned on BOOTFS being set
There is no longer any code generated at run-time
(the sysroot.mount drop-in is an unavoidable gratuitous cp).
The flow of BOOTFS{,FLAGS} from zfs-env-bootfs.service to sysroot.mount
is not noted explicitly in dracut.zfs(7), because (a) at some point it's
just visual noise and (b) it's already ordered via d-p-m.s from z-i.t.
Backport-of: 3399a30ee02d0d31ba2d43d0ce0a2fd90d5c575d
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
2023-03-28 20:49:50 +00:00
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| _____________________/|
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2022-04-04 23:14:49 +00:00
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|/ \(da
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contrib: dracut: fix race with root=zfs:dset when necessities required
This had always worked in my testing, but a user on hardware reported
this to happen 100%, and I reproduced it once with cold VM host caches.
dracut-zfs-generator runs as a systemd generator, i.e. at Some
Relatively Early Time; if root= is a fixed dataset, it tries to
"solve [necessities] statically at generation time".
If by that point zfs-import.target hasn't popped (because the import is
taking a non-negligible amount of time for whatever reason), it'll see
no children for the root datase, and as such generate no mounts.
This has never had any right to work. No-one caught this earlier because
it's just that much more convenient to have root=zfs:AUTO, which orders
itself properly.
To fix this, always run zfs-nonroot-necessities.service;
this additionally simplifies the implementation by:
* making BOOTFS from zfs-env-bootfs.service be the real, canonical,
root dataset name, not just "whatever the first bootfs is",
and only set it if we're ZFS-booting
* zfs-{rollback,snapshot}-bootfs.service can use this instead of
re-implementing it
* having zfs-env-bootfs.service also set BOOTFSFLAGS
* this means the sysroot.mount drop-in can be fixed text
* zfs-nonroot-necessities.service can also be constant and always
enabled, because it's conditioned on BOOTFS being set
There is no longer any code generated at run-time
(the sysroot.mount drop-in is an unavoidable gratuitous cp).
The flow of BOOTFS{,FLAGS} from zfs-env-bootfs.service to sysroot.mount
is not noted explicitly in dracut.zfs(7), because (a) at some point it's
just visual noise and (b) it's already ordered via d-p-m.s from z-i.t.
Backport-of: 3399a30ee02d0d31ba2d43d0ce0a2fd90d5c575d
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
2023-03-28 20:49:50 +00:00
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| sysroot.mount \(<-\(em\(em\(em dracut-zfs-generator
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| \(da
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| initrd-root-fs.target \(<-\(em zfs-nonroot-necessities.service
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2022-04-04 23:14:49 +00:00
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| \(da |
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\(da dracut-mount.service |
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zfs-snapshot-bootfs.service | |
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| \(da |
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\(da … |
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zfs-rollback-bootfs.service | |
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| \(da |
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contrib: dracut: fix race with root=zfs:dset when necessities required
This had always worked in my testing, but a user on hardware reported
this to happen 100%, and I reproduced it once with cold VM host caches.
dracut-zfs-generator runs as a systemd generator, i.e. at Some
Relatively Early Time; if root= is a fixed dataset, it tries to
"solve [necessities] statically at generation time".
If by that point zfs-import.target hasn't popped (because the import is
taking a non-negligible amount of time for whatever reason), it'll see
no children for the root datase, and as such generate no mounts.
This has never had any right to work. No-one caught this earlier because
it's just that much more convenient to have root=zfs:AUTO, which orders
itself properly.
To fix this, always run zfs-nonroot-necessities.service;
this additionally simplifies the implementation by:
* making BOOTFS from zfs-env-bootfs.service be the real, canonical,
root dataset name, not just "whatever the first bootfs is",
and only set it if we're ZFS-booting
* zfs-{rollback,snapshot}-bootfs.service can use this instead of
re-implementing it
* having zfs-env-bootfs.service also set BOOTFSFLAGS
* this means the sysroot.mount drop-in can be fixed text
* zfs-nonroot-necessities.service can also be constant and always
enabled, because it's conditioned on BOOTFS being set
There is no longer any code generated at run-time
(the sysroot.mount drop-in is an unavoidable gratuitous cp).
The flow of BOOTFS{,FLAGS} from zfs-env-bootfs.service to sysroot.mount
is not noted explicitly in dracut.zfs(7), because (a) at some point it's
just visual noise and (b) it's already ordered via d-p-m.s from z-i.t.
Backport-of: 3399a30ee02d0d31ba2d43d0ce0a2fd90d5c575d
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
2023-03-28 20:49:50 +00:00
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| /sysroot/{usr,etc,lib,&c.} \(<-\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em/
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2022-04-04 23:14:49 +00:00
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| \(da
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| initrd-fs.target
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\e______________________ |
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\e|
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\(da
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export-zfs.sh initrd.target
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\(da \(da
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dracut-shutdown.service …
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\(da
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zfs-needshutdown.sh \(-> initrd-cleanup.service
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.Ed
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.Pp
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Compare
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.Xr dracut.bootup 7
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for the full flowchart.
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.
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.Sh DESCRIPTION
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Under dracut, booting with
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.No ZFS-on- Ns Pa /
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is facilitated by a number of hooks in the
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.Nm 90zfs
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module.
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.Pp
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Booting into a ZFS dataset requires
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.Sy mountpoint Ns = Ns Pa /
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to be set on the dataset containing the root filesystem (henceforth "the boot dataset") and at the very least either the
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.Sy bootfs
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property to be set to that dataset, or the
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.Sy root=
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kernel cmdline (or dracut drop-in) argument to specify it.
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.Pp
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All children of the boot dataset with
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.Sy canmount Ns = Ns Sy on
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with
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.Sy mountpoint Ns s
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matching
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.Pa /etc , /bin , /lib , /lib?? , /libx32 , No and Pa /usr
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globs are deemed essential and will be mounted as well.
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.Pp
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.Xr zfs-mount-generator 8
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is recommended for proper functioning of the system afterward (correct mount properties, remounting, &c.).
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.
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.Sh CMDLINE
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.Ss Standard
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.Bl -tag -compact -width ".Sy root=zfs:AUTO , root=zfs: , root=zfs , Op Sy root="
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.It Sy root=zfs:\& Ns Ar dataset , Sy root=ZFS= Ns Ar dataset
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Use
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.Ar dataset
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as the boot dataset.
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All pluses
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.Pq Sq +
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are replaced with spaces
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.Pq Sq \ .
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.
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.It Sy root=zfs:AUTO , root=zfs:\& , root=zfs , Op Sy root=
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After import, search for the first pool with the
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.Sy bootfs
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property set, use its value as-if specified as the
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.Ar dataset
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above.
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.
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.It Sy rootfstype=zfs root= Ns Ar dataset
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Equivalent to
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.Sy root=zfs:\& Ns Ar dataset .
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.
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.It Sy rootfstype=zfs Op Sy root=
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Equivalent to
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.Sy root=zfs:AUTO .
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.
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.It Sy rootflags= Ns Ar flags
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Mount the boot dataset with
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.Fl o Ar flags ;
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cf.\&
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.Sx Temporary Mount Point Properties
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in
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.Xr zfsprops 7 .
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These properties will not last, since all filesystems will be re-mounted from the real root.
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.
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.It Sy debug
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If specified,
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.Nm dracut-zfs-generator
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logs to the journal.
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.El
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.Pp
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Be careful about setting neither
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.Sy rootfstype=zfs
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nor
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.Sy root=zfs:\& Ns Ar dataset
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\(em other automatic boot selection methods, like
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.Nm systemd-gpt-auto-generator
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and
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.Nm systemd-fstab-generator
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might take precedent.
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.
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.Ss ZFS-specific
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.Bl -tag -compact -width ".Sy bootfs.snapshot Ns Op Sy = Ns Ar snapshot-name"
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.It Sy bootfs.snapshot Ns Op Sy = Ns Ar snapshot-name
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Execute
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.Nm zfs Cm snapshot Ar boot-dataset Ns Sy @ Ns Ar snapshot-name
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before pivoting to the real root.
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.Ar snapshot-name
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defaults to the current kernel release.
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.
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.It Sy bootfs.rollback Ns Op Sy = Ns Ar snapshot-name
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Execute
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.Nm zfs Cm snapshot Fl Rf Ar boot-dataset Ns Sy @ Ns Ar snapshot-name
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before pivoting to the real root.
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.Ar snapshot-name
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defaults to the current kernel release.
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.
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.It Sy spl_hostid= Ns Ar host-id
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Use
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.Xr zgenhostid 8
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to set the host ID to
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.Ar host-id ;
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otherwise,
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.Pa /etc/hostid
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inherited from the real root is used.
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.
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.It Sy zfs_force , zfs.force , zfsforce
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Appends
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.Fl f
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to all
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.Nm zpool Cm import
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invocations; primarily useful in conjunction with
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.Sy spl_hostid= ,
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or if no host ID was inherited.
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.El
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.
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.Sh FILES
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.Bl -tag -width 0
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.It Pa parse-zfs.sh Pq Sy cmdline
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Processes
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.Sy spl_hostid= .
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If
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.Sy root=
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matches a known pattern, above, provides
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.Pa /dev/root
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and delays the initqueue until
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.Xr zfs 4
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is loaded,
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.
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.It Pa zfs-import-opts.sh Pq Nm systemd No environment generator
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Turns
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.Sy zfs_force , zfs.force , No or Sy zfsforce
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into
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.Ev ZPOOL_IMPORT_OPTS Ns = Ns Fl f
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for
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.Pa zfs-import-scan.service
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or
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.Pa zfs-import-cache.service .
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.
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.It Pa zfs-load-key.sh Pq Sy pre-mount
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Loads encryption keys for the boot dataset and its essential descendants.
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.Bl -tag -compact -offset 4n -width ".Sy keylocation Ns = Ns Sy https:// Ns Ar URL , Sy keylocation Ns = Ns Sy http:// Ns Ar URL"
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.It Sy keylocation Ns = Ns Sy prompt
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Is prompted for via
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.Nm systemd-ask-password
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thrice.
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.
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.It Sy keylocation Ns = Ns Sy https:// Ns Ar URL , Sy keylocation Ns = Ns Sy http:// Ns Ar URL
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.Pa network-online.target
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is started before loading.
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.
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.It Sy keylocation Ns = Ns Sy file:// Ns Ar path
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If
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.Ar path
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doesn't exist,
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.Nm udevadm No is Cm settle Ns d .
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If it still doesn't, it's waited for for up to
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.Sy 10 Ns s .
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.El
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.
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.It Pa zfs-env-bootfs.service Pq Nm systemd No service
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After pool import, sets
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.Ev BOOTFS Ns =
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in the systemd environment to the first non-null
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.Sy bootfs
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value in iteration order.
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.
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.It Pa dracut-zfs-generator Pq Nm systemd No generator
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Generates
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.Pa sysroot.mount Pq using Sy rootflags= , No if any .
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If an explicit boot dataset was specified, also generates essential mountpoints
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.Pq Pa sysroot-etc.mount , sysroot-bin.mount , No &c.\& ,
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otherwise generates
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.Pa zfs-nonroot-necessities.service
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which mounts them explicitly after
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.Pa /sysroot
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using
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.Ev BOOTFS Ns = .
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.
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.It Pa zfs-snapshot-bootfs.service , zfs-rollback-bootfs.service Pq Nm systemd No services
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Consume
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.Sy bootfs.snapshot
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and
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.Sy bootfs.rollback
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as described in
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.Sx CMDLINE .
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Use
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.Ev BOOTFS Ns =
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if no explicit boot dataset was specified.
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.
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.It Pa zfs-needshutdown.sh Pq Sy cleanup
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If any pools were imported, signals that shutdown hooks are required.
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.
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.It Pa export-zfs.sh Pq Sy shutdown
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Forcibly exports all pools.
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.
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.It Pa /etc/hostid , /etc/zfs/zpool.cache , /etc/zfs/vdev_id.conf Pq regular files
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Included verbatim, hostonly.
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.
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.It Pa mount-zfs.sh Pq Sy mount
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Does nothing on
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.Nm systemd
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systems
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.Pq if Pa dracut-zfs-generator No succeeded .
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Otherwise, loads encryption key for the boot dataset from the console or via plymouth.
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It may not work at all!
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.El
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.
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.Sh SEE ALSO
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.Xr dracut.bootup 7 ,
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.Xr zfsprops 7 ,
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.Xr zpoolprops 7 ,
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.Xr dracut-shutdown.service 8 ,
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.Xr systemd-fstab-generator 8 ,
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.Xr systemd-gpt-auto-generator 8 ,
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.Xr zfs-mount-generator 8 ,
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.Xr zgenhostid 8
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