The system won’t boot. Now what?
/boot partition?Get a recovery/rescue/live image from which to boot. Most distros provide one.
The Debian installer has a rescue mode.
At the installer “boot:” prompt, enter rescue/enable=true (on a RedHat-derived system: linux rescue).
Move through the first few steps of the installer.
At what would normally be the disk partitioning stage, we can select a partition to mount, including partitions on RAID or LVM volumes.
Once selected, installer dumps us into a shell on that partition.
At that point, with our filesystem mounted, we must diagnose the problem.
If we need to reinstall the boot loader on the master boot record, for example, run grub-install '(hd0)'.
It may be necessary to remount a read-only filesystem as read-write:
# mount -o remount,rw /
To mount all filesystems found in /etc/fstab:
# mount --all
If we don’t know the names of all physical partitions:
# fdisk -l
If we don’t know the names of all LVM physical volumes, volume groups, or logical volumes, use pvdisplay, vgdisplay or lvdisplay.
If we’ve mounted the root partition in at a temporary mount point, and now want to change it it as root:
# chroot /mnt/tmproot
Fix broken grub (assuming we have the final/real /boot/ partition mounted):
# grub-install /dev/sdX
# grub-install --recheck /dev/sdX
# grub-install --recheck /dev/sdX
Mount the root partition:
# mount /dev/sdXN /mnt
Bind mount other necessary partitioins:
# for i in /sys /proc /run /dev; do sudo mount --bind "$i" "/mnt$i"; done
Use parted or fdisk -l to find our EFI partition. It will have an “esp” flag and/or “EFI” type. Mount this partition.
# sudo mount /dev/sdXN /mnt/boot/efi
Change to our real root:
# chroot /mnt
Try to update grub:
# update-grub
If that doesn’t work, reinstall grub:
# grub-install /dev/sdX
# update-grub
grub-install and update-grub actually dogrub-install should create the EFI boot entries. We can double-check this like:
% efibootmgr -v
update-grub (re)generates a grub config file at /boot/grub/grub.cfg.