A: Go to the linux kernel:
Linux system boot into the guidance screen, select: CentOS Linux (3.10.0-693.e17.x86_64) 7 (Core), press the letter "E" key to enter the edit mode Linux kernel.
Two: linux kernel were compiled;
After entering the Linux kernel mode, find the line that begins with Linux16 at the end, enter: rd.break, then hold down the Ctrl + x to boot into rescue mode
Three: Enter the code:
switch_root:/#mount -o remount rw /sysroot
switch_root:/#chroot /sysroot
sh-4.2 # LANG = C
sh-4.2#passwd
Touch-4.2 # /.autorelabel SH // make SELinux into effect, if you do not perform, modify the password is not in force.
sh-4.2#exit
switch_root:/#reboot
*** Remember: you need to sh-4.2 # exit mode, you can use the reboot command to restart