How to Reset root password Redhat-7
Restart your linux machine and pause it on grub screen by using up/down arrow keys
Now press “e” on kernel boot line .
Go at the end of “linux16” line .
And add “console=tty1 rd.break” at end of the line and press Ctrl+x for boot .
Note : don’t confuse with “\” it automatically add for continue the word while end the line you have to just enter console=tty1 rd.break and Ctrl+x .
It will drop you in terminal here run below command .
#mount –o remount,rw /sysroot ( mount the root filesystem with read,Write permission )
#chroot /sysroot (for access root shell )
#passwd (for change root password )
#touch /.autorelabel ( for auto restored SeLinux Context to default will not effect by our modifications )
Now you can login with new password .