Outline

Users, Groups, Passwords

Users and groups provide access control
- Users have access to their own home directories, …
- Groups can provide common access settings to multiple users
- e.g. sudo is a group on Debian systems that provides administrative permissions
Create users with useradd
Change passwords with passwd
View users in a group with getent group <group-name>
Add and remove users from a group using usermod

Linux applications
Generally installed via terminal
Different distros use different package managers
Debian: apt (dpkg)
- apt update
- apt install <package>
- apt remove <package>
Fedora/RHEL: dnf (rpm)
- dnf install <package>
- dnf remove <package>

Operating systems treat each running application as a process
- Every process has a Process ID (PID) and a parent
- init has PID=1 and is started by kernel
- init brings up user services (e.g. Graphical User Interface, WiFi, …)
Processes can be killed (pkill, kill, killall)
systemd – suite for managing processes
- We can ask systemd to start processes at startup
- View startup data with systemd-analyze
- Operates like a task scheduler for applications
- Used on a majority of Linux distros (some use OpenRC instead, I’m sure there are others as well)
- Controlled with systemctl