Sudo Cheatsheet
sudo
Linux System is much secured than any of its counterpart. One of the way to implement security in Linux is the user management policy and user permission. ‘Regular users’ are not authorized to perform any system operations. If a user needs to perform any system wide changes he needs to use ‘su‘ or ‘sudo‘ command.
‘su’ Vs ‘sudo’
‘su‘ forces you to share your root password to other users whereas ‘sudo‘ makes it possible to execute system commands without root password. ‘sudo‘ lets you use your own password to execute system commands i.e., delegates system responsibility without root password.
What is ‘sudo’?
‘sudo‘ is a root binary setuid, which executes root commands on behalf of authorized users and the users need to enter their own password to execute system command followed by ‘sudo‘.
Who can execute ‘sudo’?
We can run ‘/usr/sbin/visudo‘ to add/remove the list of users who can execute ‘sudo‘.
$ sudo /usr/sbin/visudo
The sudo list looks like the below string, by default:
root ALL=(ALL) ALL
Note: You must be root to edit /usr/sbin/visudo file.
Granting sudo Access
In many situations, System Administrator, specially new to the field finds the string “root ALL=(ALL) ALL” as a template and grants unrestricted access to others which may be potentially very harmful. Editing ‘/usr/sbin/visudo’ file to something like the below pattern may really be very dangerous, unless you believe all the listed users completely.
root ALL=(ALL) ALL adam ALL=(ALL) ALL tom ALL=(ALL) ALL mark ALL=(ALL) ALL
sudo Parameters
A properly configured ‘sudo‘ is very flexible and number of commands that needs to be run may be precisely configured. The Syntax of configured ‘sudo‘ line is:
User_name Machine_name=(Effective_user) command
The above Syntax can be divided into four parts:
- User_name: This is the name of ‘sudo‘ user.
- Machine_name: This is the host name, in which ‘sudo‘ command is valid. Useful when you have lots of host machines.
- (Effective_user): The ‘Effective user’ that are allowed to execute the commands. This column lets you allows users to execute System Commands.
- Command: command or a set of commands which user may run.
Some Examples
You have a user database_punk which is a Database Administrator. You are supposed to provide him all the access on Database Server (beta.n0where.net) only, and not on any host. For the above situation the ‘sudo‘ line can be written as:
database_punk beta.n0where.net=(ALL) ALL
User ‘system_punk‘ which is supposed to execute system command as user other than root on the same Database Server. For the above situation the ‘sudo‘ line can be written as:
database_punk beta.n0where.net=(system_punk) ALL
User ‘dog_punk‘ which is supposed to run command ‘dog‘ only:
database_punk beta.n0where.net=(dog_punk) dog
What if the user needs to be granted several commands? If the number of commands, user is supposed to run is under 10, we can place all the commands alongside, with white space in between them, as shown below:
database_punk beta.n0where.net=(dog_punk) /usr/bin/command1 /usr/sbin/command2 /usr/sbin/command3 ...
If this list of command varies to the range, where it is literally not possible to type each command manually we need to use aliases.
Aliases! Yeah the Linux utility where a long-lengthy command or a list of command can be referred as a small and easy keyword. A few alias Examples, which can be used in place of entry in ‘sudo‘ configuration file.
User_Alias ADMINS=tom,jerry,adam user_Alias WEBMASTER=henry,mark
WEBMASTERS WEBSERVERS=(www) APACHE Cmnd_Alias PROC=/bin/kill,/bin/killall, /usr/bin/top
It is possible to specify a System Groups, in place of users, that belongs to that group just suffixing ‘%’ as below:
%apacheadmin WEBSERVERS=(www) APACHE
How about executing a ‘sudo‘ command without entering password? We can execute a ‘sudo‘ command without entering password by using ‘NOPASSWD‘ flag.
adam ALL=(ALL) NOPASSWD: PROCS
Here the user ‘adam‘ can execute all the commands aliased under “PROCS”, without entering a password. “Sudo” provides you a robust and safe environment with loads of flexibility as compared to ‘su‘. Moreover “sudo” configuration is easy. Some Linux distributions have “sudo” enabled by default while most of the distros of today needs you to enable it as a Security Measure. To add a user (bob) to sudo just run the below command as root.
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