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218 lines
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4.5 KiB
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218 lines
No EOL
4.5 KiB
Text
[[restoring-bootloader-using-live-disk]]
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= Restoring the bootloader using the Live disk.
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Sometimes, especially after a secondary operating systems has been installed,
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the master boot record gets damaged which then prevents the original Linux system
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from booting.
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If this happens, it is necessary to reinstall *GRUB2* to recreate the original
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settings. The process not only discovers all installed operating systems, but
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usually adds them to the *GRUB2* configuration files, so they will all become
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bootable by *GRUB2*.
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.Before you start
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* Get the Fedora Live ISO from link:https://download.fedoraproject.org/pub/fedora/linux/releases/[getfedora.org].
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* Prepare a bootable device using the downloaded ISO, either a CD or a USB.
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.Procedure
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. Boot the Fedora live system from the bootable device you have created.
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. Open the terminal.
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. Examine the partition layout and identify the `/boot` and the `/root` partition.
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+
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----
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# fdisk -l
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----
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. Follow the <<btrfs-steps, BTRFS steps>> (Fedora 33 or newer) or <<lvm-steps, LVM steps>> (older than Fedora 33) to recover your system.
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[[btrfs-steps]]
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== BTRFS steps
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If your `/root` partition is encrypted by LUKS, it must be decrypted:
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. Make sure the crypt module is in use:
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+
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----
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# modprobe dm-crypt
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----
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. Decrypt the `/root` partition (e.g. `/dev/sda3`):
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+
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----
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# cryptsetup luksOpen /dev/sda3 myvolume
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----
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+
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The decrypted device (i.e. `myvolume`) will be accessible under `/dev/mapper/`.
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Mount the `/root` partition:
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* For LUKS:
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+
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----
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# mount /dev/mapper/myvolume /mnt -o subvol=root
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----
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* For non-LUKS:
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+
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----
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# mount /dev/sda3 /mnt -o subvol=root
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----
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Mount the `/boot` partition (e.g. `/dev/sda2)`:
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----
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# mount /dev/sda2 /mnt/boot
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----
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Mount system processes and devices into the `/root` filesystem:
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----
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# mount -o bind /dev /mnt/dev
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# mount -o bind /proc /mnt/proc
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# mount -o bind /sys /mnt/sys
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# mount -o bind /run /mnt/run
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----
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On UEFI systems, bind the `efivars` directory and mount the EFI system partition (e.g. `/dev/sda1`):
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----
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# mount -o bind /sys/firmware/efi/efivars /mnt/sys/firmware/efi/efivars
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# mount /dev/sda1 /mnt/boot/efi
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----
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Change your filesystem to the one mounted under `/mnt/`:
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----
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# chroot /mnt/
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----
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Re-install GRUB:
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* On UEFI systems, several packages are required:
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+
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----
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/]# dnf reinstall shim-* grub2-efi-* grub2-common
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----
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* On BIOS systems, specify the disk (e.g. `/dev/sda`) where GRUB should be installed:
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+
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----
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/]# grub2-install /dev/sda
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----
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Re-generate the GRUB configuration file:
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----
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/]# grub2-mkconfig -o /boot/grub2/grub.cfg
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----
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Sync and exit the chroot:
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----
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/]# sync && exit
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----
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Reboot the system.
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[[lvm-steps]]
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== LVM steps
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If your `/root` partition is encrypted by LUKS, it must be decrypted:
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. Make sure the crypt module is in use:
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+
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----
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# modprobe dm-crypt
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----
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. Decrypt the `/root` partition (e.g. `/dev/sda3`):
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+
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----
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# cryptsetup luksOpen /dev/sda3 myvolume
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----
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. Scan the LVM volumes for the volume group corresponding to the `/root` partition:
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+
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----
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# vgscan
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----
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. Activate the volume group (e.g. `fedora_localhost-live`):
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+
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----
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# vgchange -ay fedora_localhost-live
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----
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. Find the logical volume corresponding to `/root`:
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+
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----
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# lvs
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----
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The logical volume will be accessible under `/dev/mapper/`.
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Create a `root` directory under `/mnt`:
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----
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# mkdir -p /mnt/root
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----
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Mount the logical volume (e.g. `/dev/mapper/fedora_localhost--live-root`) corresponding to the `/root` partition:
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----
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# mount /dev/mapper/fedora_localhost--live-root /mnt/root
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----
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Mount the `/boot` partition (e.g. `/dev/sda2`):
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----
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# mount /dev/sda2 /mnt/root/boot
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----
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Mount system processes and devices into the `/root` filesystem:
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----
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# mount -o bind /dev /mnt/root/dev
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# mount -o bind /proc /mnt/root/proc
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# mount -o bind /sys /mnt/root/sys
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# mount -o bind /run /mnt/root/run
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----
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On UEFI systems, bind the `efivars` directory and mount the EFI system partition (e.g. `/dev/sda1`):
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----
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# mount -o bind /sys/firmware/efi/efivars /mnt/root/sys/firmware/efi/efivars
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# mount /dev/sda1 /mnt/root/boot/efi
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----
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Change your filesystem to the one mounted under `/mnt/root`:
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----
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# chroot /mnt/root/
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----
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Re-install GRUB and re-generate the GRUB configuration file:
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* On UEFI systems, several packages are required:
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+
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----
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/]# dnf reinstall shim-* grub2-efi-* grub2-common
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/]# grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg
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----
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* On BIOS systems, specify the disk (e.g. `/dev/sda`) where GRUB should be installed:
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+
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----
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/]# grub2-install /dev/sda
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/]# grub2-mkconfig -o /boot/grub2/grub.cfg
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----
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Sync and exit the chroot:
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----
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/]# sync && exit
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----
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Reboot the system. |