Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/man/man7/dracut.zfs.7
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1 .\" SPDX-License-Identifier: 0BSD 2 .\" 3 .Dd April 4, 2022 4 .Dt DRACUT.ZFS 7 5 .Os 6 . 7 .Sh NAME 8 .Nm dracut.zfs 9 .Nd overview of ZFS dracut hooks 10 . 11 .Sh SYNOPSIS 12 .Bd -literal -compact 13 parse-zfs.sh \(-> dracut-cmdline.service 14 | \(da 15 | … 16 | \(da 17 \e\(em\(em\(em\(em\(em\(em\(em\(em\(-> dracut-initqueue.service 18 | zfs-import-opts.sh 19 zfs-load-module.service \(da | | 20 | | sysinit.target \(da | 21 \(da | | zfs-import-scan.service \(da 22 zfs-import-scan.service \(da \(da | zfs-import-cache.service 23 | zfs-import-cache.service basic.target | | 24 \e__________________| | \(da \(da 25 \(da | zfs-load-key.sh 26 zfs-env-bootfs.service | | 27 \(da \(da \(da 28 zfs-import.target \(-> dracut-pre-mount.service 29 | \(ua | 30 | dracut-zfs-generator | 31 | ____________________/| 32 |/ \(da 33 | sysroot.mount \(<-\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em dracut-zfs-generator 34 | | \(da | 35 | \(da sysroot-{usr,etc,lib,&c.}.mount | 36 | initrd-root-fs.target \(<-\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em or \(da 37 | | zfs-nonroot-necessities.service 38 | \(da | 39 \(da dracut-mount.service | 40 zfs-snapshot-bootfs.service | | 41 | \(da | 42 \(da … | 43 zfs-rollback-bootfs.service | | 44 | \(da | 45 | 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/ 46 | | 47 | \(da 48 | initrd-fs.target 49 \e______________________ | 50 \e| 51 \(da 52 export-zfs.sh initrd.target 53 | | 54 \(da \(da 55 dracut-shutdown.service … 56 | 57 \(da 58 zfs-needshutdown.sh \(-> initrd-cleanup.service 59 .Ed 60 .Pp 61 Compare 62 .Xr dracut.bootup 7 63 for the full flowchart. 64 . 65 .Sh DESCRIPTION 66 Under dracut, booting with 67 .No ZFS-on- Ns Pa / 68 is facilitated by a number of hooks in the 69 .Nm 90zfs 70 module. 71 .Pp 72 Booting into a ZFS dataset requires 73 .Sy mountpoint Ns = Ns Pa / 74 to be set on the dataset containing the root filesystem (henceforth "the boot 75 dataset") and at the very least either the 76 .Sy bootfs 77 property to be set to that dataset, or the 78 .Sy root= 79 kernel cmdline (or dracut drop-in) argument to specify it. 80 .Pp 81 All children of the boot dataset with 82 .Sy canmount Ns = Ns Sy on 83 with 84 .Sy mountpoint Ns s 85 matching 86 .Pa /etc , /bin , /lib , /lib?? , /libx32 , No and Pa /usr 87 globs are deemed essential and will be mounted as well. 88 .Pp 89 .Xr zfs-mount-generator 8 90 is recommended for proper functioning of the system afterward (correct mount 91 properties, remounting, &c.). 92 . 93 .Sh CMDLINE 94 .Ss Standard 95 .Bl -tag -compact -width ".Sy root=zfs:AUTO , root=zfs: , root=zfs , Op Sy root=" 96 .It Sy root=zfs:\& Ns Ar dataset , Sy root=ZFS= Ns Ar dataset 97 Use 98 .Ar dataset 99 as the boot dataset. 100 All pluses 101 .Pq Sq + 102 are replaced with spaces 103 .Pq Sq \ . 104 . 105 .It Sy root=zfs:AUTO , root=zfs:\& , root=zfs , Op Sy root= 106 After import, search for the first pool with the 107 .Sy bootfs 108 property set, use its value as-if specified as the 109 .Ar dataset 110 above. 111 . 112 .It Sy rootfstype=zfs root= Ns Ar dataset 113 Equivalent to 114 .Sy root=zfs:\& Ns Ar dataset . 115 . 116 .It Sy rootfstype=zfs Op Sy root= 117 Equivalent to 118 .Sy root=zfs:AUTO . 119 . 120 .It Sy rootflags= Ns Ar flags 121 Mount the boot dataset with 122 .Fl o Ar flags ; 123 cf.\& 124 .Sx Temporary Mount Point Properties 125 in 126 .Xr zfsprops 7 . 127 These properties will not last, since all filesystems will be re-mounted from 128 the real root. 129 . 130 .It Sy debug 131 If specified, 132 .Nm dracut-zfs-generator 133 logs to the journal. 134 .El 135 .Pp 136 Be careful about setting neither 137 .Sy rootfstype=zfs 138 nor 139 .Sy root=zfs:\& Ns Ar dataset 140 \(em other automatic boot selection methods, like 141 .Nm systemd-gpt-auto-generator 142 and 143 .Nm systemd-fstab-generator 144 might take precedent. 145 . 146 .Ss ZFS-specific 147 .Bl -tag -compact -width ".Sy bootfs.snapshot Ns Op Sy = Ns Ar snapshot-name" 148 .It Sy bootfs.snapshot Ns Op Sy = Ns Ar snapshot-name 149 Execute 150 .Nm zfs Cm snapshot Ar boot-dataset Ns Sy @ Ns Ar snapshot-name 151 before pivoting to the real root. 152 .Ar snapshot-name 153 defaults to the current kernel release. 154 . 155 .It Sy bootfs.rollback Ns Op Sy = Ns Ar snapshot-name 156 Execute 157 .Nm zfs Cm snapshot Fl Rf Ar boot-dataset Ns Sy @ Ns Ar snapshot-name 158 before pivoting to the real root. 159 .Ar snapshot-name 160 defaults to the current kernel release. 161 . 162 .It Sy spl_hostid= Ns Ar host-id 163 Use 164 .Xr zgenhostid 8 165 to set the host ID to 166 .Ar host-id ; 167 otherwise, 168 .Pa /etc/hostid 169 inherited from the real root is used. 170 . 171 .It Sy zfs_force , zfs.force , zfsforce 172 Appends 173 .Fl f 174 to all 175 .Nm zpool Cm import 176 invocations; primarily useful in conjunction with 177 .Sy spl_hostid= , 178 or if no host ID was inherited. 179 .El 180 . 181 .Sh FILES 182 .Bl -tag -width 0 183 .It Pa parse-zfs.sh Pq Sy cmdline 184 Processes 185 .Sy spl_hostid= . 186 If 187 .Sy root= 188 matches a known pattern, above, provides 189 .Pa /dev/root 190 and delays the initqueue until 191 .Xr zfs 4 192 is loaded, 193 . 194 .It Pa zfs-import-opts.sh Pq Nm systemd No environment generator 195 Turns 196 .Sy zfs_force , zfs.force , No or Sy zfsforce 197 into 198 .Ev ZPOOL_IMPORT_OPTS Ns = Ns Fl f 199 for 200 .Pa zfs-import-scan.service 201 or 202 .Pa zfs-import-cache.service . 203 . 204 .It Pa zfs-load-key.sh Pq Sy pre-mount 205 Loads encryption keys for the boot dataset and its essential descendants. 206 .Bl -tag -compact -offset 4n -width ".Sy keylocation Ns = Ns Sy https:// Ns Ar URL , Sy keylocation Ns = Ns Sy http:// Ns Ar URL" 207 .It Sy keylocation Ns = Ns Sy prompt 208 Is prompted for via 209 .Nm systemd-ask-password 210 thrice. 211 . 212 .It Sy keylocation Ns = Ns Sy https:// Ns Ar URL , Sy keylocation Ns = Ns Sy http:// Ns Ar URL 213 .Pa network-online.target 214 is started before loading. 215 . 216 .It Sy keylocation Ns = Ns Sy file:// Ns Ar path 217 If 218 .Ar path 219 doesn't exist, 220 .Nm udevadm No is Cm settle Ns d . 221 If it still doesn't, it's waited for for up to 222 .Sy 10 Ns s . 223 .El 224 . 225 .It Pa zfs-env-bootfs.service Pq Nm systemd No service 226 After pool import, sets 227 .Ev BOOTFS Ns = 228 in the systemd environment to the first non-null 229 .Sy bootfs 230 value in iteration order. 231 . 232 .It Pa dracut-zfs-generator Pq Nm systemd No generator 233 Generates 234 .Pa sysroot.mount Pq using Sy rootflags= , No if any . 235 If an explicit boot dataset was specified, also generates essential mountpoints 236 .Pq Pa sysroot-etc.mount , sysroot-bin.mount , No &c.\& , 237 otherwise generates 238 .Pa zfs-nonroot-necessities.service 239 which mounts them explicitly after 240 .Pa /sysroot 241 using 242 .Ev BOOTFS Ns = . 243 . 244 .It Pa zfs-snapshot-bootfs.service , zfs-rollback-bootfs.service Pq Nm systemd No services 245 Consume 246 .Sy bootfs.snapshot 247 and 248 .Sy bootfs.rollback 249 as described in 250 .Sx CMDLINE . 251 Use 252 .Ev BOOTFS Ns = 253 if no explicit boot dataset was specified. 254 . 255 .It Pa zfs-needshutdown.sh Pq Sy cleanup 256 If any pools were imported, signals that shutdown hooks are required. 257 . 258 .It Pa export-zfs.sh Pq Sy shutdown 259 Forcibly exports all pools. 260 . 261 .It Pa /etc/hostid , /etc/zfs/zpool.cache , /etc/zfs/vdev_id.conf Pq regular files 262 Included verbatim, hostonly. 263 . 264 .It Pa mount-zfs.sh Pq Sy mount 265 Does nothing on 266 .Nm systemd 267 systems 268 .Pq if Pa dracut-zfs-generator No succeeded . 269 Otherwise, loads encryption key for the boot dataset from the console or via 270 plymouth. 271 It may not work at all! 272 .El 273 . 274 .Sh SEE ALSO 275 .Xr dracut.bootup 7 , 276 .Xr zfsprops 7 , 277 .Xr zpoolprops 7 , 278 .Xr dracut-shutdown.service 8 , 279 .Xr systemd-fstab-generator 8 , 280 .Xr systemd-gpt-auto-generator 8 , 281 .Xr zfs-mount-generator 8 , 282 .Xr zgenhostid 8
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