Start your RHEL / CentOS 7/8 Linux machine. Upon the boot-loader appears, press any key except Enter to interrupt the countdown.
Now press "e" key to alter the current entry, where we can modify the default boot-loader entry and log in to emergency mode.
With the cursor keys, you can navigate to the line that starts with Linux. Also, need to append systemd.unit=emergency.target to the end of the line.
Later press Ctrl + x key to boot using the modified configuration.
Log in to the emergency mode by entering the root password.
Use the mount command to remount the / file system read/write. This will enable you to edit the file system.
# mount -o remount,rw /
You should be able to rescue a broken system from the emergency mode.