The idea and the purpose

In this article I want to answer this question: How can I restrict the normal user to run only limited set of commands.

So I describe step-by-step the method to create a linux user able to access to the console of a linux server but with limited permission to run commands. This method is useful when, for example, you want to give access to one of your collaborators without risking that he can launch commands as an administrator.

The idea is to use the restricted shell rbash and declare which commands the user are able to run.

The step-by-step guide

1. create the new user

   adduser <username>
   

   compile all the requested fields. The most important is the password that will be used to access the server (for example in SSH).

2. set the rbash as shell for the new user

   chsh -s /bin/rbash <username>
   

3. create a bin directory under the user home directory

   mkdir /home/<username>/bin
   chmod 755 /home/<username>/bin/
   

4. change the user's default PATH to the bin directory

   echo "PATH=$HOME/bin" >> /home/<username>/.bashrc
   echo "export PATH" >> /home/<username>/.bashrc
   

5. create symlinks of the command(s) that the user require to bin directory under the user home directory

   ln -s /bin/ping /home/<username>/bin/
   ln -s /bin/traceroute /home/<username>/bin/
   ln -s /bin/htop /home/<username>/bin/
   ln -s /bin/top /home/<username>/bin/
   ln -s /bin/df /home/<username>/bin/
   ln -s /bin/bmon /home/<username>/bin/
   ln -s /bin/ps /home/<username>/bin/
   ln -s /bin/date /home/<username>/bin/
   ln -s /bin/netstat /home/<username>/bin/
   ln -s /bin/free /home/<username>/bin/
   

6. restrict the user from modifying ~/.bashrc

   chattr +i /home/<username>/.bashrc
   

These are the basic steps to achieve the purpose. However, I want to add one more of non-core but stylistic step: print the list of available commands when the user login in console. For this purpose I user motd.

1. create motd 99-available-commands

   touch /etc/update-motd.d/99-available-commands
   

2. add the list of available commands

   cat << EOF >> /etc/update-motd.d/99-available-commands
   #!/bin/sh
   export TERM=xterm-256color
   echo "$(tput setaf 4)-------------------------------------------------------------------------------
   -- Available commands:
   -------------------------------------------------------------------------------$(tput setaf 7)
   bmon          - Bandwidth monitor and rate estimator
   date          - Display the current time or system date
   df            - Report file system disk space usage
   free          - Display amount of free and used memory in the system
   htop          - Interactive process viewer
   netstat       - Display ethernet and protocol info and statistics
   ping          - Verify IP level connectivity
   ps            - Display information about running processes
   top           - Display Linux processes
   traceroute    - Trace the path/hop from one network to another
   $(tput setaf 4)-------------------------------------------------------------------------------$(tput setaf 7)
   "
   EOF
   

3. set the right permission to the file

   chmod 755 /etc/update-motd.d/99-available-commands
   

Now the user when logging in will see a list of enabled commands like this

Thanks to

• Victor Wong for you comment in this StackOverflow discussion
• my evoseed team