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Thread: HOWTO: Password protect your GRUB entries

  1. #1
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    HOWTO: Password protect your GRUB entries

    If you don't want someone booting your machine without permission, you can add a password to your GRUB entries. You can add a password only to specific entries if you wish; this will require a user to enter a password before loading only those boot entries you protect. This can be useful when done on your Recovery Mode entries, which bring up a passwordless root login by default.

    To get started, let's first encrypt the password we want to use. Open up a terminal and enter the grub command. This brings up a grub shell. In this shell, enter the md5crypt command. When prompted, type in the password you want on your grub entries. (Don't worry, this won't write anything to your files!) After pressing Enter, you will be given an encrypted password string. Copy the string to your clipboard. Enter quit to exit the grub shell and return to bash.

    Code:
        GNU GRUB  version 0.95  (640K lower / 3072K upper memory)
    
     [ Minimal BASH-like line editing is supported.  For the first word, TAB
       lists possible command completions.  Anywhere else TAB lists the possible
       completions of a device/filename. ]
    
    grub> md5crypt
    
    Password: *************
    Encrypted: $1$w7Epf0$vX6rxpozznLAVxZGkcFcs.
    
    grub>
    Now that we have an encrypted password, it's time to add it to grub. Using sudo, open up /boot/grub/menu.lst using your favorite text editor.

    After the "initrd" line for each entry you want to password protect, start a new line beginning with password --md5 and paste in your newly-encrypted password. Using the above example password on the i386 recovery entry, this:
    Code:
    title Ubuntu, kernel 2.6.8.1-2-386 (recovery mode)
            root (hd1,2)
            kernel /boot/vmlinuz-2.6.8.1-2-386 root=/dev/hdb3 ro single
            initrd /boot/initrd.img-2.6.8.1-2-386

    Becomes this:
    Code:
    title Ubuntu, kernel 2.6.8.1-2-386 (recovery mode)
            root (hd1,2)
            kernel /boot/vmlinuz-2.6.8.1-2-386 root=/dev/hdb3 ro single
            initrd /boot/initrd.img-2.6.8.1-2-386
            password --md5 $1$w7Epf0$vX6rxpozznLAVxZGkcFcs.
    You must add such a line after every entry you want to password protect. As I mentioned earlier, I password protected my recovery mode entries out of sheer paranoia.

    Save the file, and reboot. (The first time you try this, I suggest only doing it to one entry so you can test it to make sure it works, and you can still use another entry to boot your machine in case something went wrong.)

    For a bit of added peace of mind, you can prevent everyone except root from reading /boot/grub/menu.lst by doing:

    Code:
    sudo chmod 600 /boot/grub/menu.lst
    $ whatis themeaningoflife
    themeaningoflife: not found

  2. #2
    Join Date
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    Re: HOWTO: Password protect your GRUB entries

    Let's add a few disclaimers:

    WARNING #1: This is not failproof. Duh, nothing ever is. It doesn't take much effort to pull out a LiveCD and bypass this.

    WARNING #2: Don't use an 'important password' for this! The password can be read through a LiveCD and such. Yes -- even if you do chmod it. And you can't store GRUB on an encrypted partition, either! LOL.
    Quote Originally Posted by tuxradar
    Linux's audio architecture is more like the layers of the Earth's crust than the network model, with lower levels occasionally erupting on to the surface, causing confusion and distress, and upper layers moving to displace the underlying technology that was originally hidden

  3. #3
    poptones Guest

    If you don't want someone booting your computer...

    Don't leave it alone.

    If you want to make sure your information is reasonably secure when you're not around, move /home, /var, /tmp and /root into /usr and encrypt /usr. If you want to make sure no one can even boot it, setup a bios password and lock the case.

    Oh... and make sure you always turn the machine off when you're not around.

    Anything else is just adding inconvenience for nothing.
    Last edited by poptones; December 11th, 2004 at 04:26 PM.

  4. #4
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    Re: HOWTO: Password protect your GRUB entries

    Quote Originally Posted by jdong View Post
    WARNING #2: Don't use an 'important password' for this! The password can be read through a LiveCD and such. Yes -- even if you do chmod it. And you can't store GRUB on an encrypted partition, either! LOL.
    They can only read the md5sum, don't they? And as far as I know it's almost impossible to retain the password from a dirty md5 hash like the ones created by md5crypt (dirty means there are random characters inserted).

  5. #5
    Join Date
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    Ubuntu 12.04 Precise Pangolin

    Re: HOWTO: Password protect your GRUB entries

    Quote Originally Posted by jdong View Post
    Let's add a few disclaimers:

    WARNING #1: This is not failproof. Duh, nothing ever is. It doesn't take much effort to pull out a LiveCD and bypass this.

    WARNING #2: Don't use an 'important password' for this! The password can be read through a LiveCD and such. Yes -- even if you do chmod it. And you can't store GRUB on an encrypted partition, either! LOL.
    what if you also password protect BIOS settings and you don't allow the comp to be booted via CDROM? I think the combination of grub and bios password protected is a good solution.. if you assume that nobody would steal your comp and mount the hard disk on another machine

  6. #6
    Join Date
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    Re: HOWTO: Password protect your GRUB entries

    what if i have a dual boot system with ubuntu & windoze? i set up a password to my ubuntu recovery mode boot. so, do i also have to set up a password to a windoze boot? and how to do that???

    toxic

  7. #7
    Join Date
    Apr 2006
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    53

    Re: HOWTO: Password protect your GRUB entries

    Now I have to enter password every time I boot.

    Is it possible to make GRUB ask for password only if somebody tries to edit GRUB lines during boot (wants to boot into single user mode) or disable GRUB editing during boot (disable 'e' key)?


    EDIT: And the answere is:
    If I put
    password --md5 $1$w7Epf0$vX6rxpozznLAVxZGkcFcs.
    before kernels and titles (check menu.lst, where password is commented out),
    I get what I want
    Last edited by virx; May 9th, 2007 at 06:55 AM.

  8. #8
    Join Date
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    Re: HOWTO: Password protect your GRUB entries

    This "guide" is really imprecise!
    You don't need to manually add the password line to every boot stanza you want to lock!
    Also in this way you don't secure the interactive prompt!

    You add the password line before any boot stanza, just as showed in the file's comments.

    Then you add a line that says:
    Code:
    lock
    to any static entry you wish to password protect. Static entry are before the line
    Code:
    ### BEGIN AUTOMAGIC KERNELS LIST
    and after
    Code:
    ### END DEBIAN AUTOMAGIC KERNELS LIST
    Any non-linux os as a static entry.

    For recovery mode, you want to change the line:
    Code:
    # lockalternative=false
    to:
    Code:
    # lockalternative=true
    Leaving the initial comment.
    After that you run
    Code:
    update-grub
    .
    This way every time you update the kernel, the recovery entry will be locked automatically.

    Please fix the first post.
    Last edited by soul_rebel; May 23rd, 2007 at 06:39 AM.
    Adopt an unanswered post!

    Do not learn unix like "type this to do that", get some real knowledge.
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  9. #9
    Join Date
    May 2007
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    1

    Re: HOWTO: Password protect your GRUB entries

    The last time I checked, most computers these days offer a "Hard Drive Lock" password option in their BIOS. Using this means that even if your HDD is moved to a different computer, or a liveCD is used, the data still cannot be read from the drive. That alone is a pretty decent measure to prevent people from booting your computer without your permission. A little off topic as it doesn't cover GRUB, but all the same it does deal with boot-time security.

  10. #10
    Join Date
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    Re: HOWTO: Password protect your GRUB entries

    does grub-md5-crypt use salt? i read that hashes without salt are much easier to crack.

    toxic

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