https://wiki.archlinux.org/index.php/Permissions
https://wiki.archlinux.org/index.php/Users_and_groups

usermod -aG <additional_groups> <username>
gpasswd -a|--add <username> <group>
gpasswd -d|--delete <username> <group>


- Go to the Grub-Menu (e) line of Linux 16 and change
ro
with
rw init=/sysroot/bin/sh.

- Now press Control+x to start on single user mode.

- Now access the system with this command.
chroot /sysroot
- Reset the password.
passwd root
- Update selinux information
touch /.autorelabel
- Exit chroot
exit
- Reboot your system
reboot


login:
/etc/login.defs
/etc/pam.d/
/etc/pam.d/system-auth
/etc/security/access.conf
  commented out