I have Windows and Linux installed on the same older hard drive. Windows uses an MBR/legacy BIOS boot setup, while Manjaro Linux was installed in UEFI mode. Windows is on /dev/sda5, its legacy boot information is associated with /dev/sda2, and Linux is on /dev/sda8. At the moment, Linux boots through UEFI and Windows can only be started by selecting the legacy BIOS option in the firmware boot menu. Other people in my household need to use Windows, so I would like to add Windows as an entry in GRUB instead of requiring them to open the firmware boot menu. Is that possible, and what would be the safest way to configure it?
2 Answers
Linux can boot on an MBR/legacy system, so the more reliable fix would be to boot or reinstall Manjaro in legacy mode and configure both systems consistently. A normal Linux installation should then detect Windows and add it to GRUB automatically. Before changing anything, make a full backup because boot-mode changes can leave either system unbootable.
If the disk and operating systems support it, converting the drive from MBR to GPT and getting Windows to boot through UEFI would avoid the mismatch. That conversion is not completely risk-free and Windows has its own requirements, so verify backups and compatibility first. Once both systems use UEFI, GRUB can normally present both operating systems in one menu.
So the safest choices are either to use the same boot mode for both systems or leave Windows as the default firmware option, rather than forcing a mixed-mode GRUB setup.