I don't dare to do as in the title.
So I set root password first with sudo passwd root
, and then I change all other users to be standard user, none administrator, so no user can sudo
.
If I want to set a administrator, just su root
with the password just set.
But now I wonder what happens if I didn't set root password in the beggining and then change all users to be standard user. Does it mean then this OS cannot be configured by sudoers forever? Is there any method to set new administrator?
Best Answer
What Would Happen
If you configure your system so that no users are administrators, then no one will be able to perform administrative tasks as
root
withsudo
(or its graphical frontends, such asgksu
,gksudo
, andkdesudo
) or PolicyKit. Assuming theroot
account remains disabled, you will not be able to log in asroot
(even from a virtual console) orsu
-to-root
either. Barring possible security vulnerabilities, this would prevent anyone from performing administrative tasks in the running system.Fixing the Problem
However, if you did this, the problem would still be easily fixed, assuming you have physical access to the machine. Fixing this problem is similar to resetting a forgotten password, except you add the user to the
sudo
and/oradmin
groups withusermod
, rather than resetting their password withpasswd
.Here's one method:
Boot into recovery mode by holding Shift while booting and selecting it. Select the option for a
root
shell. You'll get a shell with a#
prompt (rather than the usual$
). This means it's aroot
shell. Any command you run here is run asroot
.If you know your username, skip this step. To find out your username, run
ls /home
. This is a pretty reliable way to list the usernames of the human users of your system (while omitting user accounts likewww-data
andnobody
which are used internally but don't represent real people).Run these commands to add
username
to the necessary group(s) to be an administrator. (Replaceusername
with the actual username.)This separately attempts to add the user to the
sudo
andadmin
groups. In Ubuntu releases up to Ubuntu 11.10, administrators were in theadmin
group. In Ubuntu 12.04 (and in future releases), administrators are in thesudo
group; if a 12.04 system was upgraded from a previous release, both groups will exist.So you can put the user in just one, if you know which one, or you can just run those two commands and put them in whichever exists. I advise doing this with two commands so that if one group doesn't exist, the error doesn't stop
usermod
from attempting to add the user to the other group.Recovery mode is usually accessible. But occasionally it may be broken, disabled, or require a password, in which case you can boot from a live CD,
chroot
into the installed system, and run theusermod
commands. Here's a procedure for doing that, adapted from my considerably more general answer here:If you don't already have one, burn an Ubuntu live CD/DVD (on Ubuntu, Windows, or Mac OS X) or write an Ubuntu live USB flash drive (on Ubuntu, Windows, or Mac OS X).
In your Ubuntu system (not the live CD/DVD/USB system), run the following command in the Terminal (Ctrl+Alt+T). You do not need to be an administrator to do this.
You should include the spaces before
on
and after/
.That command produces something like
/dev/sda1 on / type ext4 (rw,errors=remount-ro,commit=0)
as the output. The text beforeon
(not including the space) is the device name of the partition that contains your Ubuntu system's root filesystem. Remember it (or write it down).Boot the computer from the live CD/DVD/USB and select
Try Ubuntu without installing
(notInstall Ubuntu
).Run these commands, replacing
/dev/sda1
with the device name of the partition containing your Ubuntu system's root filesystem, if different (andusername
with the name of the user account you wish to give administrative abilities).As with the other method, you can use
ls /home
(run this after thechroot
command) to see a list of users on the machine, if you don't know the username.Alternatives to Eliminating Administrators
On Ubuntu, when you're an administrator, you still need to authenticate with
sudo
or PolicyKit to perform actions asroot
. This is considered to be at least as secure as usingsu
to perform actions as root, since anyone who can compromise your account in such a way to read your own password (forsudo
) can also readroot
's password (forsu
). Furthermore, there are some substantial advantages (explained here) ofsudo
oversu
, and enabling theroot
account, while quite possible, is neither recommended nor officially supported in Ubuntu.If you decide that even though
sudo
and PolicyKit require your password to perform actions asroot
, you still want yourself and all other human users on your machine to run as a standard user (and not as an administrator who can run commands asroot
), you have two easy options:You can enable the
root
account, but this is discouraged as explained above. Also, by default you will not be able to log in to a graphical session asroot
, and you should not configure your system to allow this, as it's particularly dangerous to run an entire graphical desktop environment asroot
(a security bug in any part of it could compromise your system). Also, most GUI programs are not tested asroot
so there may be substantial usability bugs. If you do enableroot
, you should only ever log on as root from a virtual console (or usesu
).The better option is to just create another user account for administrative purposes. Make this account an administrator. Having a non-
root
account that can perform administrative tasks withsudo
and PolicyKit does not force you to use that account for day-to-day, non-administrative tasks.However, most users are best off with the default--where at least one user account is an administrator and can perform administrative tasks, but must (re)enter their password to do so.