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i want to know how to change the user name of my root account from root to xyz.

Also I want to know how to remove the option of boot into rescue mode from grub option at the boot time.

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These might be better posted as separate questions. –  WarriorIng64 Nov 13 '11 at 7:44
    
You should not change the username for root. This will break things. –  Thomas W. Apr 19 '12 at 23:12
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4 Answers 4

To secure your machine from unwanted root access we can disable the discovery root terminal in Grub2 by uncommenting the following line in /etc/default/grub:

GRUB_DISABLE_RECOVERY="true"

Note: To avoid security issues by editing GRUB2 entries while booting we may also want to restrict access to Grub boot menu by setting GRUB_HIDDEN_TIMEOUT=0 and enabling the OS_PROBER to prevent calling scripts in /etc/grub.d.

To take effect we also want to run the following command:

sudo update-grub

This will not prevent booting into a root environment with a live CD.

Therefore we also need to disable CD-ROM, Network or USB booting features in BIOS. To prevent BIOS changes we also need a password for BIOS access, and a hardware lock for your case to prevent resetting BIOS on your motherboard.

In addition your harddisk may have to be encrypted in case your hardware gets stolen.

Warning: By securing your system in this way you may completely lock yourself out of your computer. Be careful what you do and proceed only if you know exactly what you do. Keep your passwords in a safe place.

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You can still boot into recovery mode editing a boot entry and appending single to the kernel line. –  enzotib Nov 13 '11 at 12:17
    
@enzotib: ty - this may be important. Added a note to my anwer. –  Takkat Nov 13 '11 at 16:14
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  1. Don't think the name of root can be changed.

  2. In /etc/default/grub, uncomment (remove the '#' symbol) the following line:

    #GRUB_DISABLE_LINUX_RECOVERY="true"
    

...then run sudo update-grub.

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please help me to change to root username –  coder Nov 13 '11 at 8:14
    
As said, I don't think it can be changed. Can I ask why, what's wrong with root. –  mikewhatever Nov 13 '11 at 8:17
    
just for knowlegde –  coder Nov 13 '11 at 8:22
    
The root login is disabled in Ubuntu, so there really is no point in renaming it. –  mikewhatever Nov 13 '11 at 8:52
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Renaming the root account

NOT RECOMMENDED But if you really want to, use sudo vipw and sudo vipw -s to rename “root” in the /etc/passwd and /etc/shadow files respectively. That’s all there is to it; to the kernel, root is any user with UID 0 (at least that’s my novice understanding). Notice that if you do this, sudo -i no longer works, but sudo -u xyz -i does, and still drops you into a root prompt.

Securing console access

  1. Physically lock the PC case so it can’t be opened.

  2. Prevent the computer from booting other devices.

    In the BIOS, edit the boot sequence so that it will only boot the hard drive (and not from CD, USB device, etc.). Then set a BIOS password to prevent someone from editing the boot sequence.

  3. Disable the recovery mode option in Grub.

    Edit the file /etc/default/grub. Uncomment the line:

    #GRUB_DISABLE_LINUX_RECOVERY="true"
    
  4. Add a Grub superuser. This has the side-effect of preventing unauthenticated Grub users from editing boot lines (like adding the single parameter to boot into single-user mode and get root).

    First, hash the password you want to use for the Grub superuser account:

    grub-mkpasswd-pbkdf2
    

    Then add the superuser to the Grub config by appending the following lines to /etc/grub.d/00_header (yes, include the cat and EOF lines):

    cat << EOF
    set superusers=[YOUR USERNAME]
    password_pbkdf2 [YOUR USERNAME] [YOUR grub.pbkdf2.sha512.10000.... PASSWORD STRING]
    EOF
    

    (Example taken from http://www.g0hl1n.net/node/16.)

    Finally, run the following to have the Grub configuration changes take effect:

    sudo update-grub2
    

What this does (assuming we have truly secured the BIOS and Grub) is reduce the attack surface to the physical security of the PC (i.e. break the case lock) and the security of Ubuntu when it’s online. The goal is to make it so someone can’t walk up to the PC, reboot it, go into single-user mode, give themselves root access, and then walk away — all in under a minute. Even if you are running full-disk encryption (yet still booting the kernel + initrd off of the PC hard drive), all these steps can still be a good idea, since it is trivial to perform the same attack in order to add a keylogger to the initrd that will sniff the encryption passphrase.

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Changing the 'root' username may break things. You should not change the 'root' username. –  Thomas W. Apr 19 '12 at 23:11
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Changing the root username is NOT recommended - you are likely to break your install messing around as root.

For a definition of root and it's privileges see this article - and the reasons for not changing it are on this Ubuntu Forums Thread.

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