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4.6 KiB
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221 lines
No EOL
4.6 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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+
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. Mount the `/boot` partition (e.g. `/dev/sda2)`.
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+
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----
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# mount /dev/sda2 /mnt/boot
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----
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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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----
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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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+
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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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----
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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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+
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. Change your filesystem to the one mounted under `/mnt/`.
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+
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----
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# chroot /mnt/
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----
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+
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. Re-install *GRUB2*.
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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 *GRUB2* 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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+
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. Re-generate the *GRUB2* configuration file.
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+
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----
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/]# grub2-mkconfig -o /boot/grub2/grub.cfg
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----
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+
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. Sync and exit the chroot.
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+
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----
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/]# sync && exit
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----
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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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----
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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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----
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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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----
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# mount /dev/sda2 /mnt/root/boot
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----
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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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----
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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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+
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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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----
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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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----
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# chroot /mnt/root/
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----
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. Re-install *GRUB2* and re-generate the *GRUB2* 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 *GRUB2* should be installed.
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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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----
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/]# sync && exit
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----
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+
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. Reboot the system. |