리눅스 root 비밀번호 잃어버렸을때

https://www.rootusers.com/how-to-reset-root-user-password-in-centos-rhel-7/

http://allthatlinux.com/dokuwiki/doku.php?id=root_%ED%8C%A8%EC%8A%A4%EC%9B%8C%EB%93%9C_%EB%B3%80%EA%B2%BD#redhat_7_%EB%B3%80%EA%B2%BD_%EB%B0%A9%EB%B2%95