Rescue mode provides a convenient single-user environment and allows you to repair your system in situations when it is unable to complete a normal booting process. In rescue mode, the system attempts to mount all local file systems and start some important system services, but it does not activate network interfaces or allow more users to be logged into the system at the same time. In Red Hat Enterprise Linux 7, rescue mode is equivalent to single user mode and requires the root password.

If you already logged in as root and want to enter into emergency mode, log in to your console first as emergency mode de-activate your network interfaces. To enter type systemctl emergency.

[root@linuxlab01 ~]# systemctl emergency

Or you can also enter into rescue mode during the system boot. Select the kernel you want to enter on your grub 2 boot screen, press the “e” key to edit

Look for the line start with “linux16” and add systemd.unit=rescue.target

Press Ctrl+x to boot the system

It prompt for root password

You should be able to perform maintenance tasks like fdisk , fsck , ping or edit the files using “vi“.