For RHEL7 system
1, restart the virtual host, the boot screen appears, press the edit page e into the kernel
2, in which the parameter linux 16 additionally rearmost row "rd.break" parameter, the program run the modified Ctrl + X
3, about half a minute after the following
mount -o remount, rw / sysroot # file system read-only mode to a read mode, can be modified
chroot / sysroot # change root
passwd
touch /.autorelabel # make selinux take effect, otherwise the system will not boot properly
exit
reboot