linux recovery

systemd unable to mount cgroup due to unknown option “memory_recursiveprot” either upgrade kernel or add kernal parameter systemd.unified_cgroup_hierarchy=0

boot using live CD with kali 2022.3 and chroot into installed linux

ventoy supports booting from multiple ISOs (installer, rescue, etc) on USB drive

• 7GB USB has kali 2024.02 and grml 2024.02

setup grml-rescueboot which allows booting grml ISO from grub

rollback to snapshot

• find name of device
  • mount | grep subvol
• mount root partition to /mnt
  • sudo mount /dev/xxx -o subvol=/ /mnt
• move the old root away
  • sudo mv /mnt/@ /mnt/@_badroot
• roll back to a previous snapshot
  • sudo snapper list
  • sudo btrfs subvolume snapshot /mnt/@.snapshots/xxx/snapshot /mnt/@
• reboot
  • sudo reboot -f
• delete badroot, must be mounted first
  • sudo btrfs subvolume delete /mnt/@_badroot

btrfs config

• see /etc/snapper/configs/root
  • on boot snapshots
  • hourly snapshots
  • apt pre/post snapshots
• add root to /etc/default/snapper

rollback does not undo changes to /boot/efi as it is a separate partition

• grub in /boot/efi may become incompatible with /boot/grub
• solution is to switch to rEFIind and boot kernel directly
  • requires btrfs drivers setup in ESP
  • kernal params setup in /boot/refind_linux.conf

rEFInd does not support btrfs snapshots

• keep grub-efi around to boot from snapshot