In Linux (and Unix in general), there is a superuser named root. The Windows analog of root is Administrator. The superuser can do anything and everything, and thus doing daily work as the superuser can be dangerous. You could type a command incorrectly and crash the system. Ideally, you run as a user that has only the privileges needed for the task at hand. In some cases, this is necessarily root, but most of the time it is a regular user.
By default, the root account is locked in Ubuntu. This means you cannot login as root or use su. Instead, the installer will setup sudo to allow the user that is created during install to run all administrative commands.
This means that in the terminal you can use sudo for commands that require root privileges. All programs in the menu will use a graphical sudo to prompt for a password. When sudo asks for a password, it needs YOUR USER Password; this means that a root password is not needed.
- The password is stored by default for 15 minutes. After that time, you will need to enter your password again.
Your password will not be shown on the screen as you type it, not even as a row of stars (******). It is going in, however!
To run the graphical configuration utilities with sudo, simply launch the application via the menu.
To run a program using sudo that normally is run as the user, such as gedit, press Alt+F2 and enter gksudo gedit.
For users of Kubuntu, use kdesu in replacement for gksudo.
Ubuntu 5.10 (Breezy Badger) users, go to Applications --> System Tools --> Run as different user.
To use sudo on the command line, preface the command with sudo, as below:
sudo chown bob:bob /home/bob/*
sudo /etc/init.d/networking restart
NEVER use sudo to start graphical programs. You should always use gksudo or kdesu to run such programs, otherwise new login attempts may fail. If this happens and at login an error message reports: "Unable to read ICE authority file", log in using the failsafe terminal and execute the command below substituting user for your username.
To start a root shell (i.e. a command window where you can run root commands) use:
Allowing other users to run sudo
To add a new user to sudo, open the Users and Groups tool from System --> Administration menu. Then click on the user and then on properties. Choose the User Privileges tab. In the tab, find Executing system administration tasks and check that.
In the terminal this would be: sudo adduser $user admin, where you replace $user with the name of the user.
Benefits of using sudo
The benefits of leaving root disabled by default include the following:
- The installer has to ask fewer questions
- Users don't have to remember an extra password, which they are likely to forget
It avoids the "I can do anything" interactive login by default -you will be prompted for a password before major changes can happen, which should make you think about the consequences of what you are doing.
Sudo adds a log entry of the command(s) run (In /var/log/auth.log). If you mess up, you can always go back and see what commands were run. It is also nice for auditing.
Every cracker trying to brute-force their way into your box will know it has an account named root and will try that first. What they don't know is what the usernames of your other users are.
Allows easy transfer for admin rights, in a short term or long term period, by adding and removing users from groups, while not compromising the root account.
- sudo can be setup with a much more fine-grained security policy
Downsides of using sudo
Although for desktops the benefits of using sudo are great, there are possible issues which need to be noted:
Redirecting the output of commands run with sudo can catch new users out. For instance consider sudo ls > /root/somefile will not work since it is the shell that tries to write to that file. You can use ls | sudo tee -a /root/somefile to append, or ls | sudo tee /root/somefile to overwrite contents.
- In a lot of office environments the ONLY local user on a system is root. All other users are imported using NSS techniques such as nss-ldap. To setup a workstation, or fix it, in the case of a network failure where nss-ldap is broken, root is required. This tends to leave the system unusable unless cracked. An extra local user, or an enabled root password is needed here.
Isn't sudo less secure than su?
The basic security model is the same, and therefore these two systems share their primary weaknesses. Any user who uses su or sudo must be considered to be a privileged user. If that user's account is compromised by an attacker, the attacker can also gain root privileges the next time the user does so. The user account is the weak link in this chain, and so must be protected with the same care as root.
On a more esoteric level, sudo provides some features which encourage different work habits, which can positively impact the security of the system. sudo is commonly used to execute only a single command, while su is generally used to open a shell and execute multiple commands. The sudo approach reduces the likelihood of a root shell being left open indefinitely, and encourages the user to minimize their use of root privileges.
I won't be able to enter single-user mode!
- The sulogin program in Ubuntu is patched to handle the default case of a locked root password.
I can get a root shell from the console without entering a password!
Console users have access to the boot loader, and can gain administrative privileges in various ways during the boot process. For example, by specifying an alternate init(8) program. Linux systems are not typically configured to be secure at the console, and additional steps (for example, setting a root password, a boot loader password and a BIOS password) are necessary in order to make them so. Note that console users usually have physical access to the machine and so can manipulate it in other ways as well.
Going back to a traditional root account
This is not recommended!
If all you need is to be able to work on a root console you'd better use the command:
Enabling the root account
To enable the root account (i.e. set a password) use:
sudo passwd root
Enter your existing password
Enter password for root
Confirm password for root
Disabling the root account
If you have enabled a root password and wish to disable it again. To disable the root account after you have enabled it use:
sudo passwd -l root
This locks the root account.
This will also prevent you starting the computer in recovery mode on versions of Ubuntu before Ubuntu 6.06 (Dapper Drake)
- This is because the password value for root in /etc/shadow is not automatically returned to the single * character required for passwordless recovery log in as root. (You will be asked for a password, as one still exists, but will not be able to log in as it is locked.) You will need to edit /etc/shadow to prevent this problem after enabling and then locking the root account. This has been fixed for Ubuntu 6.06 (Dapper Drake) (Flight 3 onwards), locked password and null (*) password are now treated as the same when recovery mode is started.
Let sudo ask for the root password
You can make sudo ask for the root password instead of the user password, you can do this by adding the keyword rootpw to the line in /etc/sudoers that starts with Defaults.
Make certain that you don't do this if you intend to lock the root account
Enabling graphical root login
It is highly recommended NOT to allow root to login graphically!
Open System --> Administration --> Login Screen Setup
- Click on the security tab
Check Allow root login
- Open Konqueror and open the /etc/kde3/kdm/ folder
Right click the kdmrc file and then Actions --> 'Edit as root'
On line 246 should be AllowRootLogin=false change it to 'true'
- Save and exit.
From the Linux Console
- Switch to a virtual terminal with Ctrl+Alt+F1 (or F2, F3, ..., F6). You can get back to your X session with Ctrl+Alt+F7.
- Log in as yourself.
Become root with "sudo -i".
Start a new X server on display :1 with "startx -- :1".
You can run a different window manager (say, fvwm) with something like "startx fvwm -- :1".
- You must use display :1 because the default (display :0) is already being used by you.
- Be careful, you're the superuser. Don't forget to logout as soon as you're done, from both X and the console.