Sometimes, your Linux system may fail to boot due to corrupted files, misconfigured settings, or hardware issues. When that happens, you need a way to access and repair your system without loading the normal operating system. That's where rescue mode comes in handy.
Rescue mode is a special boot option that allows you to run a minimal Linux environment with basic commands and tools. You can use rescue mode to troubleshoot and fix common boot problems, such as repairing the file system, restoring the boot loader, editing configuration files, or resetting the root password.
Rescue mode is used to troubleshoot issues with the filesystem mount or boot loader, Make config changes. It is a Minimal Linux Environment where only Single user login is allowed and network connections are disabled.
Rescue mode in Linux serves as a dedicated environment for addressing filesystem and boot loader problems. It enables users to modify essential configurations and perform system recovery tasks in a restricted, single-user access setup, emphasizing local troubleshooting without network connectivity.
There are different ways to enter rescue mode depending on your Linux distribution and boot loader. For example, if you use GRUB, you can press the Esc key during the boot process to display the GRUB menu, and then select the rescue mode option. Alternatively, you can use a bootable CD, DVD, or USB drive that contains a rescue mode image, and boot from it. You may need to change the boot order in your BIOS or UEFI settings to do this.
To access rescue mode in Linux, methods vary based on your distribution and boot loader. Typically, with GRUB, you can interrupt the boot process by pressing Esc to access the GRUB menu, where you'll find an option for rescue mode. Alternatively, you can utilize a bootable CD, DVD, or USB drive containing a rescue mode image. Adjusting the boot order in your BIOS or UEFI settings may be necessary to prioritize booting from external media for this purpose.
Once you enter rescue mode, you will see a command prompt that looks something like this:
sh: can't access tty; job control turned off
/ #
This means that you are in a shell that has no access to your root partition, which is where your system files and settings are stored. To mount the root partition, you need to identify its device name, such as /dev/sda1 or /dev/vda1. You can use the fdisk -l command to list all the partitions on your system. Then, you can use the mount command to mount the root partition to a temporary directory, such as /mnt. For example: mount /dev/sda1 /mnt
To mount the root partition in rescue mode, follow these steps: Identify the Root Partition: Use fdisk -l to list all partitions and find the device name of your root partition (e.g., /dev/sda1 or /dev/vda1). Mount the Root Partition: Once identified, use mount to mount it to a temporary directory like /mnt: mount /dev/sda1 /mnt Access the Mounted Root Partition: After mounting, access files and directories under /mnt. This allows crucial system file changes or repairs. Mounting the root partition in rescue mode grants access to system files, crucial for troubleshooting and resolving boot issues or system problems effectively.
After mounting the root partition, you can use the chroot command to change the root directory to /mnt. This will allow you to run commands and tools as if you were in the normal operating system. For example: chroot /mnt /bin/bash You may also need to mount other partitions or file systems, such as /boot, /proc, /sys, or /dev, depending on your system configuration. You can use the mount -a command to mount all the entries in /etc/fstab, or mount them manually.
To chroot into the root partition after mounting it in rescue mode: Mount essential directories like /boot, /proc, /sys, or /dev with mount -a. Use chroot /mnt /bin/bash to switch the root directory to /mnt, allowing you to operate as if in the normal system. Execute commands to diagnose, repair, or configure system issues effectively. Chroot provides full access to system files, crucial for troubleshooting and resolving boot or system problems in rescue mode.
Once you are in the chrooted environment, you can use a variety of commands and tools to fix boot problems. For instance, fsck -y /dev/sda1 will check and correct any errors on the root partition. Additionally, grub-install /dev/sda will install GRUB on the MBR of the first disk. You can also open configuration files for editing using a text editor, such as vi or nano. Furthermore, passwd root will prompt you to enter a new password for the root user. After fixing the boot problems, you can exit the chrooted environment using exit and then reboot your system using reboot. Hopefully, your system will boot normally and you can get back to your work.