Booting via GRUB 2 prompt

From Jeremy Bryan Smith
Revision as of 03:53, 6 February 2021 by Jeremy (talk | contribs)
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Did your update-initramfs not complete before you rebooted your zfs-on-root Ubuntu install? Here's how to boot it from the GRUB prompt using a previous kernel, assuming that your boot filesystem is on (hd0,gpt3), the zfs dataset name of your boot filesystem is bpool/BOOT/ubuntu/HEAD, the zfs dataset name of your root filesystem is rpool/ROOT/ubuntu/HEAD, and you're wanting to boot version 5.4.0-42-generic of the kernel: 

grub> insmod zfs
grub> set root=(hd0,gpt3)
grub> linux /BOOT/ubuntu/HEAD/@/vmlinuz-5.4.0-42-generic boot=zfs zfs_force=1 root=ZFS=rpool/ROOT/ubuntu/HEAD net.ifnames=0 biosdevname=0
grub> initrd /BOOT/ubuntu/HEAD/@/initrd.img-5.4.0-42-generic
grub> boot

That should load the kernel and initial ramdisk. If you are then dropped to an (initramfs) shell, you'll have to manually import the zpool containing the root filesystem: 

(initramfs) /sbin/modprobe zfs
(initramfs) zpool import rpool -R /root
(initramfs) exit

Note: The following: 

net.ifnames=0 biosdevname=0

was added to the kernel parameters to ensure that all Ethernet device names use the naming scheme ethX for consistency. That part is not necessary.

You'll then want to update your initial ramdisk and re-install GRUB to be on the safe side.

  • Verify /boot is mounted from your boot pool:
root@daytapod1 ~ $ findmnt /boot/
TARGET SOURCE                 FSTYPE OPTIONS
/boot  bpool/BOOT/ubuntu/HEAD zfs    rw,nodev,noatime,xattr,posixacl
  • Update initial ramdisks for all kernels:
root@daytapod1 ~ $ update-initramfs -k all -u -v
  • Install grub on all disks in the boot pool:
root@daytapod1 ~ $ zpool status bpool
  pool: bpool
 state: ONLINE
  scan: scrub repaired 0B in 00:00:03 with 0 errors on Sun Jan 10 00:24:04 2021
config:

        NAME                                                STATE     READ WRITE CKSUM
        bpool                                               ONLINE       0     0     0
          ata-Hitachi_HUA722020ALA330_JK1151YAH6E00Z-part3  ONLINE       0     0     0

errors: No known data errors

root@daytapod1 ~ $ grub-install /dev/disk/by-id/ata-Hitachi_HUA722020ALA330_JK1151YAH6E00Z
Installing for i386-pc platform.
Installation finished. No error reported.
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