Restoring the GRUB Bootloader on Manjaro Linux

Manjaro Linux GRUB (especially on dual-boot systems with Windows) may sometimes get corrupted and fail to boot. Possible error messages include

Reboot and select proper Boot Device

or

error: unknown filesystem
Entering rescue mode...

For me, this is almost guaranteed to happen after performing a REISUB. It can also randomly occur when rebooting/cold-booting after a major system update.

Solution

Note

If your system is on EFI, Ensure that you boot into the USB rescue drive using EFI mode (the menu option you pick at the boot menu has to be the one containing 'EFI'). If your system is on BIOS, pick the menu option without 'EFI'.

---

A solution posted in the comments that is receiving lots of positive feedback made by @y6nH seems to be the right steps to fix it:

These are the steps that worked for me, without having to install any new packages:

• Boot into Manjaro installer via USB rescue drive
• Open terminal
• sudo manjaro-chroot -a (and select system to mount)
• grub-install /dev/sdXXX1965 (where sdXXX1965 is your GRUB drive, typically the same as your Manjaro installation; make sure you choose the right drive!)
• grub-install --recheck /dev/sdXXX1965
• update-grub
• exit
• shutdown
• unplug your USB rescue drive
• Boot into GRUB

For dual-boot systems, once back into Manjaro on your system, run sudo mkinitcpio -P && sudo update-grub to get Windows entries back in GRUB.