Linux System Administration Basics
Linux System Administration Basics tests routine account, process, service, package, and log management on a single Linux host. The focus is safe operational commands and understanding where configuration lives, not deep tuning.
Accounts and privilege
/etc/passwd holds account records (name, UID, GID, home, shell), /etc/shadow holds password hashes, and /etc/group holds groups. UID 0 is root. useradd -m -s /bin/bash alice creates a home and login shell; passwd alice sets a password; usermod -aG developers alice appends a supplementary group; userdel -r alice removes the account and home. sudo runs one command with elevated privilege; su switches user.
Processes, services, packages
ps aux lists processes, top shows live activity, and kill PID sends SIGTERM (15) by default; kill -9 sends SIGKILL and prevents cleanup. systemd manages units: systemctl start/stop/status/enable/disable. Package tools include apt update, apt install, apt remove on Debian-family systems and dnf install/remove on Red Hat-family systems; rpm -q verifies installed packages. Logs go to journalctl and /var/log.
Worked example
To add a developer who needs bash and the developers group: useradd -m -s /bin/bash alice usermod -aG developers alice passwd alice The -m creates /home/alice, -s sets the shell, -aG appends without dropping existing supplementary groups, and passwd sets the initial password.
Traps
usermod -G without -a replaces group membership; userdel without -r leaves the home directory; apt update refreshes metadata but does not upgrade packages; systemctl enable does not start a service now; kill -9 should not be the first choice.