How to Protect GRUB with Password in RHEL / CentOS

GRand Unified Bootloader (GRUB) is a default bootloader in all Unix-like operating system. As promised in our earlier article “How to reset a forgotten root password“, here we are going to review how to protect GRUB with password. As mentioned earlier post, anyone can login into single user mode and may change system setting as needed. This is the big security flow. So, to prevent such unauthorized person to access system we may required to have grub with password protected.

Here, we’ll see how to prevent user from entering into single user mode and changing the settings of system who may have direct or physical access of system.

Cautious: We urge to take backup of your data and try it out at your own risk.

How to Password Protect GRUB

STEP 1: Create a password for GRUB, be a root user and open command prompt, type below command. When prompted type grub password twice and press enter. This will return MD5hash password. Please copy or note it down.

[[email protected] ~]#  grub-md5-crypt

Sample Output:

[[email protected] ~]# grub-md5-crypt

Password:

Retype password:

$1$19oD/1$NklcucLPshZVoo5LvUYEp1

Step 2: Now you need to open the /boot/grub/menu.lst or /boot/grub/grub.conf file and add the MD5 password. Both files are same and symbolic link to each other.

[[email protected] ~]# vi /boot/grub/menu.lst

OR

[[email protected] ~]# vi /boot/grub/grub.conf

Note : I advise you to take backup of the files before making any changes to it, if in case something goes wrong you can revert it.

STEP 3: Add the newly created MD5 password in GRUB configuration file. Please paste copied password below timeout line and save it and exit. For example, Enter the linepassword –md5 <add the copied md5 string from step 1> above.

# grub.conf generated by anaconda

#

# Note that you do not have to rerun grub after making changes to this file

# NOTICE:  You have a /boot partition.  This means that

#          all kernel and initrd paths are relative to /boot/, eg.

#          root (hd0,0)

#          kernel /vmlinuz-version ro root=/dev/sda3

#          initrd /initrd-[generic-]version.img

#boot=/dev/sda

default=0

timeout=5

password --md5 $1$TNUb/1$TwroGJn4eCd4xsYeGiBYq.

splashimage=(hd0,0)/grub/splash.xpm.gz

hiddenmenu

title CentOS (2.6.32-279.5.2.el6.i686)

        root (hd0,0)

        kernel /vmlinuz-2.6.32-279.5.2.el6.i686 ro root=UUID=d06b9517-8bb3-44db-b8c5-7710e183edb7 rd_NO_LUKS rd_NO_LVM rd_NO_MD rd_NO_DM.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us crashkernel=auto rhgb quiet

        initrd /initramfs-2.6.32-279.5.2.el6.i686.img

title centos (2.6.32-71.el6.i686)

        root (hd0,0)

        kernel /vmlinuz-2.6.32-71.el6.i686 ro root=UUID=d06b9517-8bb3-44db-b8c5-7710e183edb7 rd_NO_LUKS rd_NO_LVM rd_NO_MD rd_NO_DM.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us crashkernel=auto rhgb quiet

        initrd /initramfs-2.6.32-71.el6.i686.img

STEP 4: Reboot system and try it pressing ‘p‘ to enter password to unlock and enable next features.

Password Protect Grub in Linux

This is how we can protect GRUB with password. Let us know how do you secure your system? via comments.

Please visit grub security online manual pages for more information at GRUB Security.