linuxexpert-practice-labs/labs/linux-terminal/3-2-security-settings

Using Linux Terminal 3.2: System-wide and per-user security settings

A process limit for one user, a message for every login shell, and a stricter umask for one user.

Before you start

The lab creates users alice and student (password Lab-Pass-1). Work as root (sudo -i) for tasks 1 and 2, and as student (sudo -iu student) for task 3. The lab saves /etc/profile, /etc/bash.bashrc and the limits files, and puts them back on reset; it also removes the files you add to /etc/profile.d and /etc/security/limits.d.

Tasks

1. Limit the user alice to 50 processes, as both soft and hard limit, in a file of its own. su - alice -c 'ulimit -u; ulimit -Hu' prints 50 twice, and other users' limits are unchanged.
2. Make every login shell print Authorized use only before the prompt, without editing /etc/profile. su - alice -c true prints the message.
3. Give student a umask of 077 in every interactive shell: in a new shell, umask prints 0077, and touch ~/x; ls -l ~/x shows -rw-------. Other users keep their umask.

Hints

• A file in /etc/security/limits.d/ with alice, - (or a soft and a hard line), nproc and 50. Limits apply at the next login.
• A .sh file in /etc/profile.d/ with an echo.
• ~/.bashrc runs in every interactive bash (and Ubuntu's ~/.profile runs it for login shells); bash starts a new one to test.