CS AO: System Administration Fundamentals

System Administration Fundamentals

This domain tests whether you understand what an administrator actually controls: the boundary between kernel space and user space, the boot chain, service supervision, and the operational discipline that keeps changes reversible.

Core rules

• Linux boot sequence: firmware (UEFI/BIOS) → bootloader (GRUB2) → initramfs → systemd as PID 1 → target units. systemctl get-default shows the target; multi-user.target is the equivalent of runlevel 3, graphical.target of runlevel 5.
• Windows equivalents: UEFI → Windows Boot Manager → winload.exe → kernel → Session Manager → Service Control Manager. services.msc and sc.exe manage service state; startup type matters more than current state.
• Least privilege: administrative tasks run through sudo with a named account, not shared root. Every privileged action should be attributable to a person.
• Change management: a change needs a reason, rollback plan, test evidence, and a window. Emergency changes are documented after the fact, not skipped.

Worked example

A web service fails after reboot but works when started manually. Reasoning: manual start uses your interactive environment; boot start uses the service manager's environment. Check systemctl status app for the exit code, then journalctl -u app -b for this boot. Common cause: the unit starts before the network or a mounted filesystem is ready, or relies on a shell profile variable. Fix with After=network-online.target and Wants=network-online.target, or declare Environment= in the unit. Verify by rebooting, not by systemctl restart.

Traps

• Confusing enabled with running: systemctl enable only creates symlinks; start runs it now.
• Assuming a service that starts manually will survive reboot.
• Editing files in /etc without a backup or version control.
• Treating documentation as optional; reproducible steps earn marks.