Written by Guillermo Garron .
Date: 2012-05-22 10:56:30 -0400
sudoers file located at:
/etc/sudoers, contains the rules that users must follow when using the sudo command.
If you have ever used used Ubuntu, you know that the root account is disabled. This is because the root password is not set in Ubuntu, you can assign one and use it as with every other Linux distribution. That anyway is another story. On normal Ubuntu Linux computers you need to use
sudo to act as root.
I like using
sudo, I’m not using Ubuntu anymore. The first thing I do when I install a new Linux is to use
visudo to edit the sudoers file. And I always give my account root rights, then I can run commands as root without switching users.
The best way to understand the
sudo command, and the rules in sudoers file, the funny way is by this comics.
|<img src=”/images/2012-05/sudo-sudoers-make-me-sandwich.png” class=”image” title=”sudo make me a sandwich||sudoers file” alt=”sudo make me a sandwich sudoers file” />|
credit to: XKCD
As you can see from this funny picture, using
sudo command, makes the system obey any given order.
The two best advantages about using
sudo command are:
- Restricted privileges
- Logs of the actions taken by users
I’m sure you are now fully aware of the advantages of using
sudo command in a daily basis, how to use it?
In order to use
sudo you first need to configure the sudoers file. The sudoers file is located at
/etc/sudoers. And you should not edit it directly, you need to use the
Once you enter
visudo command, you will see something like this:
# /etc/sudoers # # This file MUST be edited with the 'visudo' command as root. # # See the man page for details on how to write a sudoers file. # Defaults env_reset # Host alias specification # User alias specification # Cmnd alias specification # User privilege specification root ALL=(ALL) ALL
Almost all lines are commented out, the one that matters in this sudoers file example is:
root ALL=(ALL) ALL
This line means: The root user can execute from ALL terminals, acting as ALL (any) users, and run ALL (any) command.
The first part is the user, the second is the terminal from where the user can use
sudo command, the third part is which users he may act as, and the last one, is which commands he may run when using
operator ALL= /sbin/poweroff
The above command, makes the user operator can from any terminal, run the command power off.
You can also create aliases for: users -> User_Alias, run commands as other users -> Runas_Alias, host -> Host_Alias and command -> Cmnd_Alias
User_Alias OPERATORS = joe, mike, jude Runas_Alias OP = root, operator Host_Alias OFNET = 10.1.2.0/255.255.255.0 Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm
As you can see the alias OPERATORS includes the users joe, mike and jude, the alias OP includes the users root and operator, alias OFNET includes the network 10.1.2.0 (all the C class), and the command alias PRINTING includes the commands lpc and lprm.
So, a typical sudoers file may look like this:
User_Alias OPERATORS = joe, mike, jude Runas_Alias OP = root, operator Host_Alias OFNET = 10.1.2.0/255.255.255.0 Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm OPERATORS ALL=ALL #The users in the OPERATORS group can run any command from any terminal. linus ALL=(OP) ALL # The user linus can run any command from any terminal as any user in the OP group (root or operator). user2 OFNET=(ALL) ALL # user user2 may run any command from any machine in the OFNET network, as any user. user3 ALL= PRINTING # user user3 may run lpc and lprm from any machine. go2linux ALL=(ALL) ALL # user go2linux may run any command from any machine acting as any user. (like Ubuntu)
If you want not to be asked for a password use this form:
go2linux ALL=(ALL) NOPASSWD: ALL
You may want to read sudoers man page
Considering that you are still reading here a bonus:
visudo command uses
vi as the editor here some tips to use it:
- Switch to root, (su root), then run visudo, (as above).
- Find where it says “root ALL=(ALL) ALL”.
- Type “o” to insert a new line below it.
- Now type what you want to insert, eg “username ALL=(ALL) ALL”.
- Hit esc to exit insert-mode.
- Type “:x” to save and exit.
Can I change the default
Yes, changing the default
visudo editor is easy.
And just because of your dedication, and still reading until here, I’ll show you how to set
vim to use with
visudo command as default editor.
Using vim with visudo
export VISUAL=vim; visudo
Using nano with visudo
export VISUAL=nano; visudo
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My name is Guillermo Garron. I am telecommunications engineer from Bolivia
I like technology a lot, and this site is mainly dedicated to that
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