If the server kernel is faulty, you cannot log in. You can solve the problem by rescue mode, repairing the kernel, and updating the boot configuration, as follows!

This section describes the rescue mode or single user mode. Rescue mode allows the user to start the server in a minimal system environment for easy repair operations. Restart the server and press a specific key such as Esc, F2, F12, or Del to access the boot menu. Then select Rescue Mode or a similar option. The system boots into a minimization environment where troubleshooting and repair operations are performed.

When the system starts in single-user mode, only necessary services are loaded and users are allowed to log in as superusers. Step: Restart the server, press Esc to enter the GRUB menu at boot time, select the kernel version and press e to edit the boot options. Find the kernel line, start with linux, add single or 1 at the end, and press Ctrl + X or F10 to boot in single user mode.

Check and repair file systems in rescue mode or single user mode. First check and repair the file system with the fsck command:

fsck /dev/sdXn

If there are multiple partitions, you need to run the fsck command for each partition.

If the kernel is causing the problem, try updating or reinstalling the kernel. Mount the root file system in rescue mode.

mount /dev/sdXn /mnt

chroot /mnt

Update the kernel:

yum update kernel   # For RHEL/CentOS

apt-get install --reinstall linux-image-$(uname -r)  # For Debian/Ubuntu

Update GRUB configuration:

grub2-mkconfig -o /boot/grub2/grub.cfg   # For RHEL/CentOS

update-grub                             # For Debian/Ubuntu

To restart the system:

reboot

Check for possible corruption or configuration errors in the boot configuration file and try to repair it. Enter rescue mode or single user mode and mount the file system:

mount /dev/sdXn /mnt

chroot /mnt

To reinstall or repair GRUB:

grub2-install /dev/sdX   # For RHEL/CentOS

grub-install /dev/sdX    # For Debian/Ubuntu

Update GRUB configuration:

grub2-mkconfig -o /boot/grub2/grub.cfg   # For RHEL/CentOS

update-grub                             # For Debian/Ubuntu

To restart the system:

reboot

If the above methods do not work, you can start the server using a Live CD or Live USB to go deeper into the repair. Make a Live CD or Live USB. Start the server using a Live CD or Live USB. Mount the local disk and repair it.

mount /dev/sdXn /mnt

chroot /mnt

Perform repair operations as required, such as updating the kernel and repairing the boot configuration.

In summary, it is a collection of solutions for handling login errors caused by kernel failures. This operation helps you restore the server. If all else fails, you may need to restore the data from the backup or contact professional technical support.