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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. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz> Closes #14690
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‎contrib/dracut/90zfs/module-setup.sh.in‎

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@@ -81,6 +81,9 @@ install() {
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inst_simple "${moddir}/zfs-env-bootfs.service" "${systemdsystemunitdir}/zfs-env-bootfs.service"
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systemctl -q --root "${initdir}" add-wants zfs-import.target zfs-env-bootfs.service
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inst_simple "${moddir}/zfs-nonroot-necessities.service" "${systemdsystemunitdir}/zfs-nonroot-necessities.service"
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systemctl -q --root "${initdir}" add-requires initrd-root-fs.target zfs-nonroot-necessities.service
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# Add user-provided unit overrides:
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# - /etc/systemd/system/${_service}
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# - /etc/systemd/system/${_service}.d/overrides.conf

‎contrib/dracut/90zfs/zfs-env-bootfs.service.in‎

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@@ -1,14 +1,23 @@
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[Unit]
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Description=Set BOOTFS environment for dracut
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Documentation=man:zpool(8)
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Description=Set BOOTFS and BOOTFSFLAGS environment variables for dracut
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DefaultDependencies=no
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After=zfs-import-cache.service
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After=zfs-import-scan.service
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Before=zfs-import.target
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[Service]
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Type=oneshot
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ExecStart=/bin/sh -c "exec systemctl set-environment BOOTFS=$(@sbindir@/zpool list -H -o bootfs | grep -m1 -vFx -)"
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ExecStart=/bin/sh -c ' \
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. /lib/dracut-zfs-lib.sh; \
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decode_root_args || exit 0; \
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[ "$root" = "zfs:AUTO" ] && root="$(@sbindir@/zpool list -H -o bootfs | grep -m1 -vFx -)"; \
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rootflags="$(getarg rootflags=)"; \
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case ",$rootflags," in \
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*,zfsutil,*) ;; \
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,,) rootflags=zfsutil ;; \
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*) rootflags="zfsutil,$rootflags" ;; \
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esac; \
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exec systemctl set-environment BOOTFS="$root" BOOTFSFLAGS="$rootflags"'
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[Install]
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WantedBy=zfs-import.target

‎contrib/dracut/90zfs/zfs-generator.sh.in‎

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@@ -14,81 +14,24 @@ GENERATOR_DIR="$1"
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. /lib/dracut-zfs-lib.sh
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decode_root_args || exit 0
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[ -z "${rootflags}" ] && rootflags=$(getarg rootflags=)
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case ",${rootflags}," in
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*,zfsutil,*) ;;
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,,) rootflags=zfsutil ;;
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*) rootflags="zfsutil,${rootflags}" ;;
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esac
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[ -n "$debug" ] && echo "zfs-generator: writing extension for sysroot.mount to $GENERATOR_DIR/sysroot.mount.d/zfs-enhancement.conf" >> /dev/kmsg
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mkdir -p "$GENERATOR_DIR"/sysroot.mount.d "$GENERATOR_DIR"/initrd-root-fs.target.requires "$GENERATOR_DIR"/dracut-pre-mount.service.d
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mkdir -p "$GENERATOR_DIR"/sysroot.mount.d "$GENERATOR_DIR"/dracut-pre-mount.service.d
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{
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echo "[Unit]"
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echo "Before=initrd-root-fs.target"
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echo "After=zfs-import.target"
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echo
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echo "[Mount]"
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if [ "${root}" = "zfs:AUTO" ]; then
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echo "PassEnvironment=BOOTFS"
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echo 'What=${BOOTFS}'
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else
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echo "What=${root}"
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fi
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echo "PassEnvironment=BOOTFS BOOTFSFLAGS"
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echo 'What=${BOOTFS}'
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echo "Type=zfs"
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echo "Options=${rootflags}"
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echo 'Options=${BOOTFSFLAGS}'
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} > "$GENERATOR_DIR"/sysroot.mount.d/zfs-enhancement.conf
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ln -fs ../sysroot.mount "$GENERATOR_DIR"/initrd-root-fs.target.requires/sysroot.mount
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if [ "${root}" = "zfs:AUTO" ]; then
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{
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echo "[Unit]"
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echo "Before=initrd-root-fs.target"
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echo "After=sysroot.mount"
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echo "DefaultDependencies=no"
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echo
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echo "[Service]"
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echo "Type=oneshot"
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echo "PassEnvironment=BOOTFS"
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echo "ExecStart=/bin/sh -c '" ' \
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. /lib/dracut-zfs-lib.sh; \
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_zfs_nonroot_necessities_cb() { \
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zfs mount | grep -m1 -q "^$1 " && return 0; \
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echo "Mounting $1 on /sysroot$2"; \
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mount -o zfsutil -t zfs "$1" "/sysroot$2"; \
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}; \
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for_relevant_root_children "${BOOTFS}" _zfs_nonroot_necessities_cb;' \
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"'"
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} > "$GENERATOR_DIR"/zfs-nonroot-necessities.service
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ln -fs ../zfs-nonroot-necessities.service "$GENERATOR_DIR"/initrd-root-fs.target.requires/zfs-nonroot-necessities.service
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else
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# We can solve this statically at generation time, so do!
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_zfs_generator_cb() {
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dset="${1}"
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mpnt="${2}"
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unit="$(systemd-escape --suffix=mount -p "/sysroot${mpnt}")"
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{
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echo "[Unit]"
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echo "Before=initrd-root-fs.target"
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echo "After=sysroot.mount"
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echo
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echo "[Mount]"
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echo "Where=/sysroot${mpnt}"
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echo "What=${dset}"
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echo "Type=zfs"
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echo "Options=zfsutil"
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} > "$GENERATOR_DIR/${unit}"
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ln -fs ../"${unit}" "$GENERATOR_DIR"/initrd-root-fs.target.requires/"${unit}"
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}
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for_relevant_root_children "${root}" _zfs_generator_cb
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fi
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{
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echo "[Unit]"
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echo "After=zfs-import.target"

‎contrib/dracut/90zfs/zfs-lib.sh.in‎

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@@ -39,7 +39,7 @@ mount_dataset() {
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# for_relevant_root_children DATASET EXEC
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# Runs "EXEC dataset mountpoint" for all children of DATASET that are needed for system bringup
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# Used by zfs-generator.sh and friends, too!
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# Used by zfs-nonroot-necessities.service and friends, too!
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for_relevant_root_children() {
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dataset="${1}"
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exec="${2}"

‎contrib/dracut/90zfs/zfs-nonroot-necessities.service.in‎

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@@ -0,0 +1,20 @@
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[Unit]
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Before=initrd-root-fs.target
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After=sysroot.mount
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DefaultDependencies=no
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ConditionEnvironment=BOOTFS
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[Service]
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Type=oneshot
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PassEnvironment=BOOTFS
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ExecStart=/bin/sh -c ' \
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. /lib/dracut-zfs-lib.sh; \
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_zfs_nonroot_necessities_cb() { \
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@sbindir@/zfs mount | grep -m1 -q "^$1 " && return 0; \
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echo "Mounting $1 on /sysroot$2"; \
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mount -o zfsutil -t zfs "$1" "/sysroot$2"; \
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}; \
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for_relevant_root_children "${BOOTFS}" _zfs_nonroot_necessities_cb'
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[Install]
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RequiredBy=initrd-root-fs.target

‎contrib/dracut/90zfs/zfs-rollback-bootfs.service.in‎

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@@ -5,8 +5,9 @@ After=zfs-import.target dracut-pre-mount.service zfs-snapshot-bootfs.service
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Before=dracut-mount.service
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DefaultDependencies=no
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ConditionKernelCommandLine=bootfs.rollback
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ConditionEnvironment=BOOTFS
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[Service]
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Type=oneshot
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ExecStart=/bin/sh -c '. /lib/dracut-zfs-lib.sh; decode_root_args || exit; [ "$root" = "zfs:AUTO" ] && root="$BOOTFS"; SNAPNAME="$(getarg bootfs.rollback)"; exec @sbindir@/zfs rollback -Rf "$root@${SNAPNAME:-%v}"'
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ExecStart=/bin/sh -c '. /lib/dracut-lib.sh; SNAPNAME="$(getarg bootfs.rollback)"; exec @sbindir@/zfs rollback -Rf "$BOOTFS@${SNAPNAME:-%v}"'
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RemainAfterExit=yes

‎contrib/dracut/90zfs/zfs-snapshot-bootfs.service.in‎

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@@ -5,8 +5,9 @@ After=zfs-import.target dracut-pre-mount.service
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Before=dracut-mount.service
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DefaultDependencies=no
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ConditionKernelCommandLine=bootfs.snapshot
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ConditionEnvironment=BOOTFS
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[Service]
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Type=oneshot
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ExecStart=-/bin/sh -c '. /lib/dracut-zfs-lib.sh; decode_root_args || exit; [ "$root" = "zfs:AUTO" ] && root="$BOOTFS"; SNAPNAME="$(getarg bootfs.snapshot)"; exec @sbindir@/zfs snapshot "$root@${SNAPNAME:-%v}"'
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ExecStart=-/bin/sh -c '. /lib/dracut-lib.sh; SNAPNAME="$(getarg bootfs.snapshot)"; exec @sbindir@/zfs snapshot "$BOOTFS@${SNAPNAME:-%v}"'
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RemainAfterExit=yes

‎contrib/dracut/Makefile.am‎

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@@ -16,6 +16,7 @@ pkgdracut_90_SCRIPTS = \
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pkgdracut_90_DATA = \
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%D%/90zfs/zfs-env-bootfs.service \
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%D%/90zfs/zfs-nonroot-necessities.service \
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%D%/90zfs/zfs-rollback-bootfs.service \
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%D%/90zfs/zfs-snapshot-bootfs.service
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‎man/man7/dracut.zfs.7‎

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@@ -1,6 +1,6 @@
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.\" SPDX-License-Identifier: 0BSD
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.\"
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.Dd April 4, 2022
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.Dd March 28, 2023
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.Dt DRACUT.ZFS 7
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.Os
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.
@@ -28,21 +28,21 @@ zfs-import-scan.service \(da \(da | zfs-import-c
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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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| ____________________/|
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| _____________________/|
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|/ \(da
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| sysroot.mount \(<-\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em dracut-zfs-generator
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| | \(da |
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| \(da sysroot-{usr,etc,lib,&c.}.mount |
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| initrd-root-fs.target \(<-\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em or \(da
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| | zfs-nonroot-necessities.service
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| sysroot.mount \(<-\(em\(em\(em dracut-zfs-generator
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| |
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| \(da
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| initrd-root-fs.target \(<-\(em zfs-nonroot-necessities.service
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| | |
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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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| sysroot-usr.mount \(<-\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em/
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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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| |
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| \(da
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| initrd-fs.target

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