Some times it is possible to change the root password in Red hat El4 without knowing old password when the system boot. but we can prevent this one by using grub password and MD5 encryption For setting password # /sbin/grub-md5-crypt Now enter the password [root@MB327SCS068 ~]# /sbin/grub-md5-cryptPassword:Retype password:$1$plEu7$3eucnZfDe1o1fcmCAtjJ6. copy the encrypted password goto /boot/grub/grub.conf file [...]