I have a working Linux system that boots from a GPT/UEFI drive. I would like to add a windows partition to this drive, without destroying the existing boot system in the process.

Theoretically, I would need to shrink the existing BTRFS partition, and ask Windows to do its thing with the new unpartitioned space, and have Windows install its UEFI stuff to the existing EFI System Partition, which runs gumiboot (systemd boot loader), and configure gumiboot to allow me to select Linux or Windows.

Can this be done without destroying the existing configuration in the process?

  • In theory, yes. In practice, partition resizing always carries some risk, so you should be sure to back up any important data first. Also, Windows will set its own boot loader as the default, so you'll have to reset gummiboot as your preferred boot program after you install Windows. This can be done in many different ways -- bcdedit in Windows, bcfg in an EFI shell, efibootmgr in an emergency Linux disk, etc. – Rod Smith Jul 30 '15 at 19:22
  • I've got backups of the data on the partition. My motivation is avoiding the work of setting UEFI up again. It was a nightmare to get right, and took me almost 3 days. What exactly does windows do, though? Does it wipe the EFI System Partition? – mkaito Jul 30 '15 at 20:16

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