In this video shows resetting the Root Password in CentOS 7 | Break root password | Change root password on Redhat
Step:-
Step 1: Alt + Ctrl+Delete [For reset ]
Step 2: e [type]
Step 3 : go end of line
Step 4: rd.break
Step 5: Ctrl + x
Step 6: mount -o remount,rw /sysroot/
Step 7: chroot /sysroot/
Step 8: passwd root
[type new password, again type new password]
Step 9: touch /.autorelabel
Step 10: exit
Step 11: exit
Now try to log-in, new password as root
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