Password Protecting Grub

To protect grub using md5 encrypted password, we can use this simple technique-

[root@zimbra ~]# grub-md5-crypt
Password:
Retype password:
$1$zsPMx0$DkhqPFB1ouY/W7uhvCJZL1

 This command generates a MD5 encrypted password that will be added to the file grub.conf. Here is my sample file-

[root@zimbra ~]# vim /etc/grub.conf

#####################################################################################
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
password --md5 $1$zsPMx0$DkhqPFB1ouY/W7uhvCJZL1
hiddenmenu
title Red Hat Enterprise Linux (2.6.32-220.el6.x86_64)
        root (hd0,0)
        kernel /vmlinuz-2.6.32-220.el6.x86_64 ro root=/dev/mapper/vg_zimbra-lv_root rd_NO_LUKS rd_LVM_LV=vg_zimbra/lv_root LANG=en_US.UTF-8 rd_NO_MD quiet SYSFONT=latarcyrheb-sun16 rhgb crashkernel=auto rd_LVM_LV=vg_zimbra/lv_swap  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM
        initrd /initramfs-2.6.32-220.el6.x86_64.img

And we are ready. The system can be rebooted safely, and will never ask for password during booting.

However, the system will ask for a password if someone tries to access grub menu entries, for example, to get to single user mode.

Grub asking for password

Hope this helps. :)

NOTE: You could try experimenting with "password" placement in different places of grub.conf. This parameter may be used multiple times in the file.