Repair grub - encrypted and unencrypted systems

[ilu]

I'm posting here Arjen's explanation on how to repair grub using the SolydXK live system from another thread:
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For anybody who doesn't know how to do that. Here follows a short description of the steps to take to restore boot with a SolydXK live session:

Mount root partition:

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$ live-chroot /dev/sda2

In chroot: compare mounted partitions in fstab and blkid to get /boot partition(s)

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# cat /etc/fstab
# sudo blkid

In my case I have a separate /boot and /boot/efi partition (ignore this if you don't have them):

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# mount /dev/sda4 /boot
# mount /dev/sda1 /boot/efi

Install Grub2:

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# grub-install /dev/sda

Ignore the "GUID Partition Table Header signature" errors. You're in a chrooted session. The last line matters, though: "Installation finished. No error reported."

Update Grub2:

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# update-grub

Unmount /boot partition(s) and exit.

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# umount /boot/efi /boot
# exit

Now, reboot and cross your fingers.

[ilu]

If the system is encrypted, this is the way to go:

Become root:

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sudo -i

Decrypt and mount /root - check which exact partition holds /root.

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root@solydxk:~# cryptsetup luksOpen /dev/sdaX linux
Enter passphrase for /dev/sdaX: 
root@solydxk:~# live-chroot /dev/mapper/linux
/etc/live-installer-3/live-installer-3.conf: line 10: --assume-yes: command not found
/etc/live-installer-3/live-installer-3.conf: line 11: --quiet: command not found
Use configured target: /target
Create directory /target
Mounting /dev/mapper/linux on /target
Chrooting into /target

Reinstall and update grub - check which exact partition to mount.

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root@solydxk:/# mount /dev/sdaX /boot
root@solydxk:/# mount /dev/sda1 /boot/efi
root@solydxk:/# grub-install /dev/sda
Installing for i386-pc platform.
Installation finished. No error reported.
root@solydxk:/# update-grub
Generating grub configuration file ...
Found background image: .background_cache.png
Found linux image: ...
done

You might check the situation with

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root@solydxk:/# bootinfoscript

[ilu]

If you have a multiboot EFI system and it refuses to boot into the right grub environment, check which one it loads with:

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sudo efibootmgr
efibootmgr --help

to see the options. You can change the boot order there. If you need to clean up be careful not to touch anything from Microsoft, the entry named "boot" belongs to Windows. More explanation here: https://www.dedoimedo.com/computers/gru ... overy.html and here https://www.dedoimedo.com/computers/gru ... overy.html.

[ilu]

Edit: Lots of useful general info about UEFI installs here: https://ubuntuforums.org/showthread.php?t=2147295