I had installed Manajaro alongside with Debian and everything had worked fine, but today I replaced the Debian partition with Ubuntu and now I can't enter to Manjaro. when I try to enter to Manjaro partition I see this message "kernel panic - not syncing vfs unable to mount root fs on unknown-block(0 0)" The partition with ubuntu works fine.
Try the simple method first.
Manjaro's bootloader needs to be in charge. Ubuntutututu can't handle Manjaro properly.
The basic problem is most distros put themselves first in the boot order during installation. Most distros can't boot Manjaro, but Manjaro can boot most distros. Even so, using ubuntu's grub, use the manjaro fallback option to boot and then in a terminal execute
sudo grub-install to restore the boot order back to Manjaro. Then also do
sudo update-grub so that Manjaro adds the new distro to Manjaro's grub. There are many other valid methods to accomplish the same thing, but I think this is the simplest.
just reboot with USB manjaro install
open a terminal
manjaro-chroot -a ( select manjaro ) update-grub exit
Or you can choose the Manjaro bootloader in the UEFI Bios.
I'm lazy so I try the most simple solution and it work! thanks.