Memory hook: Installed is not running; running is not enabled.
Must remember
RPM is the package format/database; rpm -q checks installed packages and rpm -V verifies recorded file properties. DNF resolves dependencies and repository metadata. dnf repolist, dnf info, dnf install, dnf remove and dnf upgrade serve different jobs. Repository definitions normally live under /etc/yum.repos.d/; understand base URLs, enabled flags and signature checking.
Flatpak applications use remotes, application IDs and runtimes. flatpak remotes, flatpak search, flatpak list, flatpak install and flatpak uninstall manage this separate ecosystem. User installations and system installations differ; the account and scope must match the task.
systemctl start affects the present; enable configures boot activation. enable --now does both. disable does not automatically stop a running service; mask prevents activation via its normal unit path. Use status, is-active, is-enabled and list-units to verify. After editing a unit or drop-in, run daemon-reload before restarting the service.
journalctl -u SERVICE -b narrows logs to one service and boot; journalctl -b -1 reads the previous boot when retained. Persistent journaling requires appropriate journal storage configuration and a persistent journal directory; otherwise reboot may discard useful evidence. Traditional logs under /var/log remain relevant.
Use ps, top, free, vmstat and df to separate CPU, memory and storage pressure. kill -TERM requests graceful termination; SIGKILL cannot be handled for cleanup. A higher nice value means lower scheduling priority. nice starts with an adjustment; renice changes one. Inspect tuned-adm active and available profiles before selecting a workload-specific tuning profile.
Choose under exam pressure
| Requirement | Choice and reason |
|---|---|
| Service must survive reboot | Enable it and verify its boot behavior. |
| Find startup failure | Service status plus its boot journal. |
| Install an application from a Flatpak remote | Use Flatpak in the requested user/system scope, not DNF. |
Traps
- Masking is stronger than disabling.
- Installing a package does not prove its daemon is configured or listening.
Active recall
1. Start versus enable?
Start changes current runtime state; enable configures future activation such as boot.
2. What reloads systemd unit definitions?
systemctl daemon-reload; it is separate from restarting the application.
3. How do you inspect a prior boot?
journalctl -b -1, provided persistent logs were retained.
4. Does nice +10 increase CPU priority?
No. A larger nice value lowers scheduling priority.
5. Why prefer TERM before KILL?
TERM permits graceful handling and cleanup; KILL immediately terminates without application cleanup.