---
title: "Restore the Linux bootloader in Rescue"
sidebar_label: "Restore the Linux bootloader in Rescue"
sidebar_position: 8
description: "How to restore the Linux bootloader in Rescue recovery and diagnostics mode"
---
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# Restore the Linux bootloader in Rescue
The main bootloader for Linux operating systems is GRUB. If the Linux bootloader has been deleted, corrupted, or stopped working after a disk replacement, you can restore it. To do this, [boot the server in Rescue mode](/dedicated/troubleshooting/boot-to-recovery.mdx), mount the main partitions in the same way they are mounted in the main system, and install the GRUB bootloader.
Disk partitioning without software RAID
1. [Boot the server into Rescue recovery and diagnostics mode](/dedicated/troubleshooting/boot-to-recovery.mdx).
2. Determine the OS boot mode:
```bash
[ -d /sys/firmware/efi ] && echo "UEFI" || echo "BIOS"
```
The response will contain information about the OS boot mode — `BIOS` or `UEFI`.
3. Output information about the partitions on the disks:
```bash
lsblk -o +FSTYPE
```
The response will contain information about the partitions on the disks. For example:
```bash
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS FSTYPE
sda 8:0 0 25G 0 disk
├─sda1 8:1 0 1M 0 part
├─sda2 8:2 0 512M 0 part vfat
├─sda3 8:2 0 1G 0 part ext4
└─sda4 8:3 0 23,5G 0 part ext4
sdb 8:16 0 8G 0 disk
├─sdb1 8:17 0 4G 0 part ext4
└─sdb2 8:20 0 4G 0 part xfs
```
Here `sda1`, `sda2`, `sda3`, `sda4`, `sdb1`, `sdb2` are disk partitions. In your OS, the partition names may differ.
4. Identify the partitions that need to be mounted:
* root partition `/` — usually the largest partition on the disk; in the example in step 3, this is partition `sda4`;
* boot partition `/boot` — usually a partition with the ext4 filesystem and a size of 512 MB — 1 GB. In the example in step 3, this is partition `sda3`;
* EFI partition `/boot/efi` — used when booting the OS in UEFI mode. This is a partition with the vfat filesystem. In the example in step 3, this is partition `sda2`.
5. Mount the root filesystem to the `/mnt` directory:
```bash
mount /dev/ /mnt
```
Specify `` — the root partition `/` that you selected in step 4; in the example, this is `sda4`.
6. Mount the boot partition:
```bash
mount /dev/ /mnt/boot
```
Specify `` — the boot partition `/boot` on the disk that you selected in step 4; in the example, this is `sda3`.
7. If using the OS UEFI bootloader, mount the EFI partition:
```bash
mount /dev/ /mnt/boot/efi
```
Specify `` — the EFI partition `/boot/efi` that you selected in step 4; in the example, this is `sda2`.
8. Mount the system filesystems:
```bash
mount --bind /sys /mnt/sys
mount --bind /proc /mnt/proc
mount --bind /dev /mnt/dev
mount -t devpts devpts /mnt/dev/pts
```
9. Connect to the environment:
```bash
chroot /mnt /bin/bash
```
10. Export the PATH variable:
```bash
export export PATH=/usr/sbin:/usr/bin:/sbin:/bin:$PATH
```
11. Install the GRUB bootloader. The command depends on the OS bootloader you identified in step 2:
* UEFI:
```bash
grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=GRUB
```
* BIOS:
```bash
grub-install /dev/
```
Specify `` — the system disk where the OS is installed and the root partition `/` is located; in the example in step 3, this is `sda`.
12. Create the GRUB configuration file:
```bash
/sbin/grub-mkconfig -o /boot/grub/grub.cfg
```
13. After completing the work, exit the environment:
```bash
exit
```
14. Unmount the system filesystems:
```bash
umount -t devpts devpts /mnt/dev/pts
umount --bind /dev /mnt/dev
umount -t sysfs /sys /mnt/sys
umount -t proc /proc /mnt/proc
```
15. Unmount the filesystem:
```bash
umount /dev/ /mnt
```
Specify `` — the root partition `/` that you mounted in step 5; in the example, this is `sda4`.
Disk partitioning with software RAID
1. [Boot the server into Rescue recovery and diagnostics mode](/dedicated/troubleshooting/boot-to-recovery.mdx).
2. Determine the OS boot mode:
```bash
[ -d /sys/firmware/efi ] && echo "UEFI" || echo "BIOS"
```
The response will contain information about the OS boot mode — `BIOS` or `UEFI`.
3. Check if the system has detected RAID arrays; to do this, output information about the partitions on the disks:
```bash
lsblk -o +FSTYPE
```
The response will contain information about the partitions on the disks and the RAID array configuration. For example:
```bash
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT FSTYPE
sda 8:0 0 447.6G 0 disk
├─sda1 8:1 0 512M 0 part vfat
├─sda2 8:2 0 500M 0 part
│ └─md0 9:0 0 500M 0 raid1 ext4
└─sda3 8:3 0 446.6G 0 part
└─md1 9:1 0 446.6G 0 raid1 ext4
sdb 8:16 0 447.6G 0 disk
├─sdb1 8:17 0 512M 0 part
├─sdb2 8:18 0 500M 0 part
│ └─md0 9:0 0 500M 0 raid1 ext4
└─sdb3 8:19 0 446.6G 0 part
└─md1 9:1 0 446.6G 0 raid1 ext4
```
Here `md0`, `md1` are RAID arrays on disk partitions. In your OS, the RAID array names may differ.
4. If the output of `lsblk` in step 3 shows RAID arrays, skip this step. If there are no RAID arrays, run the assembly of RAID arrays:
```bash
mdadm --assemble --scan
```
5. Output information about the partitions on the disks and the RAID array configuration:
```bash
lsblk -o +FSTYPE
```
The response will contain information about the partitions on the disks and the RAID array configuration. For example:
```bash
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT FSTYPE
sda 8:0 0 447.6G 0 disk
├─sda1 8:1 0 512M 0 part vfat
├─sda2 8:2 0 500M 0 part
│ └─md0 9:0 0 500M 0 raid1 ext4
└─sda3 8:3 0 446.6G 0 part
└─md1 9:1 0 446.6G 0 raid1 ext4
sdb 8:16 0 447.6G 0 disk
├─sdb1 8:17 0 512M 0 part
├─sdb2 8:18 0 500M 0 part
│ └─md0 9:0 0 500M 0 raid1 ext4
└─sdb3 8:19 0 446.6G 0 part
└─md1 9:1 0 446.6G 0 raid1 ext4
```
Here `md0`, `md1` are RAID arrays on disk partitions. In your OS, the RAID array names may differ.
6. Identify the RAID partitions that need to be mounted:
* root RAID partition `/` — usually the largest partition on the disk; in the example in step 5, this is array `md1`;
* boot RAID partition `/boot` — usually a partition with the ext4 filesystem and a size of 512 MB — 1 GB. In the example in step 5, this is array `md0`;
* EFI partition `/boot/efi` — used when booting the OS in UEFI mode. This is a partition with the vfat filesystem. In the example in step 5, this is partition `sda1` and, if the EFI partition was cloned to the second disk, `sdb1`.
7. Mount the root filesystem to the `/mnt` directory:
```bash
mount /dev/ /mnt
```
Here `` — the root RAID partition that you selected in step 6; in the example, this is `md1`.
8. Mount the boot RAID partition:
```bash
mount /dev/ /mnt/boot
```
Specify `` — the boot RAID array `/boot` that you selected in step 6; in the example, this is `md0`.
9. If using the OS UEFI bootloader, mount the EFI partition:
```bash
mount /dev/ /mnt/boot/efi
```
Specify `` — the EFI partition `/boot/efi` that you selected in step 6; in the example, this is `sda1`.
10. Mount the system filesystems:
```bash
mount --bind /sys /mnt/sys
mount --bind /proc /mnt/proc
mount --bind /dev /mnt/dev
mount -t devpts devpts /mnt/dev/pts
```
11. Connect to the environment:
```bash
chroot /mnt /bin/bash
```
12. Export the PATH variable:
```bash
export PATH=/bin:/usr/bin:/usr/local/bin:/sbin:/usr/sbin:/usr/local/sbin
```
13. Install the GRUB bootloader. The command depends on the OS bootloader you identified in step 2:
* UEFI:
```bash
grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=GRUB
```
* BIOS — install the bootloader on each disk from which the OS will boot:
```bash
grub-install /dev/
grub-install /dev/
```
Specify ``, `` as the system disks where the OS is installed and the root partition `/` is located; in the example in step 5, these are `sda` and `sdb`. Depending on the number of devices in the RAID, there may be more disks.
14. Create the GRUB configuration file:
```bash
/sbin/grub-mkconfig -o /boot/grub/grub.cfg
```
15. After completing the work, exit the environment:
```bash
exit
```
16. If your system has only one EFI partition, skip this step. If the EFI partition on your system is cloned across several disks, install the GRUB bootloader on each disk:
16.1. Unmount the EFI partition:
```bash
umount /mnt/boot/efi
```
16.2. Mount the EFI partition:
```bash
mount /dev/ /mnt/efi2
```
Specify `` — the EFI partition on the second disk; in the example in step 5, this is `sdb1`.
16.3. Mount the system filesystems:
```bash
mount --bind /sys /mnt/sys
mount --bind /proc /mnt/proc
mount --bind /dev /mnt/dev
mount -t devpts devpts /mnt/dev/pts
```
16.4. Connect to the environment:
```bash
chroot /mnt /bin/bash
```
16.5. Install the GRUB bootloader:
```bash
grub-install --target=x86_64-efi --efi-directory=/efi2 --bootloader-id=GRUB
```
16.6. Create the GRUB configuration file:
```bash
/sbin/grub-mkconfig -o /boot/grub/grub.cfg
```
16.7. Exit the environment after work is complete:
```bash
exit
```
17. Unmount the system filesystems:
```bash
umount -t devpts devpts /mnt/dev/pts
umount --bind /dev /mnt/dev
umount -t sysfs /sys /mnt/sys
umount -t proc /proc /mnt/proc
```
18. Unmount the filesystem:
```bash
umount /dev/ /mnt
```
Specify `` — the root RAID partition `/` that you mounted in step 7; in the example, this is `md1`.