I've done conversions in both directions a few times although not very recently. But having done it, I'd say "f it, just reinstall". Or "f it, get drunk and sent to the hospital" is even a better experience than converting. BIOS->UEFI - BIOS install won't have an EFI System partition, so you have to shrink something. Easiest is pilfering some from the 500MB /boot. Or alternatively from the LVM partition, which is a non-trivial sequence: resize2fs, lvresize, pvmove, pvresize, vgreduce, fdisk, gdisk MBR to GPT conversion. Yay LVM by default - so this step is easier, by a lot, without LVM. - If there's a spare MBR entry (primary) available, then the ESP type code 0xEF is used. The UEFI spec says firmware should support this configuration but I don't know how well tested it is. - If converting MBR to GPT, the last partition file system needs resizing because otherwise it overlaps with the backup GPT. If the last partition is LVM (which is the default location for default installations, again yay LVM by default) you have to do the non-trivial sequence: resize2fs, lvresize, pvmove, pvresize, vgreduce, fdisk, gdisk MBR to GPT conversion. UEFI->BIOS - The 200MB FAT ESP can be blown away in favor of a 1+MB BIOS Boot quite easily. Both directions require updating fstab to varying degrees. And both require booting alternate media, such that the system is booting in the mode you are converting to, assembling the file system (easiest with anaconda rescue option at boot time from non-live install media), chrooting the mount point, reinstalling grub, creating a new grub.cfg, and rebuilding the initramfs. However, the reinstalling grub procedure is not the same between the two directions and of course the grub.cfgs go in two different locations *sigh*. For UEFI->BIOS: it's possible to just do grub2-install <dev>, and grub2-mkconfig -o /boot/grub2/grub.cfg. For BIOS->UEFI I'm pretty sure you're best off resinstalling the grub2-efi package (and installing/reinstalling the shim packages) so that you get the nice shim fallback behavior, the prebaked-signed grub, and therefore instructions work for either Secure Boot on or off. And then grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg. Summary: UEFI to BIOS conversion is either very slightly easier if you don't use LVM and don't need conversion to GPT. Otherwise it's a lot easier. Unrelated to conversion, two unfortunates exposed: the difference in grub.cfg locations; the ESP, using one of the most fragile file systems still in use, being persistently mounted rw, and too often being modified due to the grub.cfg on the ESP. Instead the ESP grub.cfg should point via configfile to the maintained grub.cfg at /boot/grub2. Then there'd be no reason at all for /boot/efi being persistently mounted. Note that neither OS X nor Windows keep their ESPs mounted. Chris Murphy -- devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/devel Fedora Code of Conduct: http://fedoraproject.org/code-of-conduct
