LINUXMAKER, OpenSource, Tutorials

Boot with the shell of Grub2 in case of problems

The loss of the boot manager from Grub 2 is dramatic, but is not really tragic: If the Linux system and its partitions are still intact, the repair can be done with simple and convenient means. Linux can also start with problems via the Grub shell.

The main task of the boot loader Grub 2 is to start the Linux kernel from the hard disk. Grub can also pass the command to other bootloaders, such as Windows, and boot systems from ISO files. This is useful, for example, for diagnostic tools or repair systems. For the investigation of the boot environment, Grub offers its own shell, via which the system can also be started manually. Operation is not very intuitive, but the Grub shell can be of great help in the event of start-up problems.

With the grub shell

Grub usually works even if something is configured incorrectly and Linux does not start because of this. The grub shell is used to analyze the grub or boot environment. In the event of errors, you usually end up in the shell automatically. If not, hold down the Shift key after turning on the PC. You will then see the Grub menu and use the C key to access the shell.

The operation of the Grub Shell is similar to that in a terminal window of the Bash Shell under Linux. Let yourself be told what commands there are



display, followed by the Enter key. Grub uses the US keyboard layout. The table "Keyboard layout in the Grub Shell" shows where you can find the characters on a German keyboard. "Pager = 1" provides for the long list for the output of one screen page at a time, with the space bar you scroll through.
You only need a few commands to start a Linux system. With


view the partitions. Tap in

ls (hd

and press the Tab key. Grub then outputs "hd0 hd1" as possible devices. Suppose Linux is installed on the first partition of the first hard disk with MBR partition style. If you

ls (hd0,

type in and then press the Tab key, Grub automatically adds "ls (hd0, msdos1)" if there is only one partition. Otherwise you see information about the possible partitions, which you then have to add yourself. Add a "/" to the end of the line, then you can use the Tab key to display folders and files. You can determine the content of a folder with followed

ls (hd0,msdos1)/boot/

by the tab key. This is where the Linux kernel and the associated ramdisk are located. A Linux system can be started with the following four lines:

set root=(hd0,msdos1)

linux /boot/vmlinuz-4.15.0-29- generic root=/dev/sd[XY] ro

initrd /boot/initrd.img-4.15.0-29 generic


Adjust the names of the files for your system, replace "/dev/sd[XY]" with the device path of the Linux installation. For "hd0, msdos1" this is "/dev/sda1", for "hd1, msdos1" use "/dev/sdb1" and so on. If the system is installed in Uefi mode, the name of the partition is, for example, "hd0, gpt2", which corresponds to "/dev/sda2" in the file system.

If Linux has been started successfully, Grub can be reinstalled in the terminal using these two command lines:

grub-install /dev/sd[X]


Replace "/dev/sd[X]" with the drive path of the hard disk on which the system is installed. With a Uefi system, "update-grub" is sufficient.