start, stop, restart Linux services (daemon HUNTING!!) // Linux for Hackers // EP 6

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About this video

Episode 6 of the Linux for Hackers series explains Linux daemons (pronounced ‘demon’ in the video) and how to manage services. A process is an instance of a running program: launching Sublime Text or nano creates a process visible with ‘ps aux’ piped to grep, and closing the program ends it. Interactive processes are user-started, while daemons run in the background with no interaction — like Windows services — handling networking, printing, SSH, and time sync; daemon names end in ’d’, as in sshd and ntpd. systemd is the master daemon and init system: it is PID 1, starts first at boot after the kernel, mounts filesystems, and forks other processes, visible via ‘pstree’. systemd calls its managed services ‘units’, and systemctl controls them. The video demonstrates, mainly on sshd and ntp: status, start, stop, restart, reload, and reload-or-restart; enable and disable to control boot startup (distinct from currently running); and is-active/is-enabled checks. ‘systemctl list-units’ shows only loaded/active units (filterable with –type=service), while ’list-unit-files’ reveals unloaded ones like the disabled nginx. Troubleshooting nginx failing to start leads to journalctl -xe, which itself yields no entries until the systemd-journald service is restarted; after that, the journal shows nginx could not bind because port 80 was already in use. The lab is Hack The Box Academy’s PwnBox, sponsor of the series.

Key takeaways

Daemons are background service processes (names end in ’d’, e.g. sshd, ntpd); find processes with ps aux | grep
systemd is PID 1, the init system and service manager; it calls services ‘units’
Core systemctl verbs: status, start, stop, restart, reload, and reload-or-restart
enable/disable controls boot startup only and does not start or stop a service now
list-unit-files finds unloaded units; journalctl -xe (after fixing journald if needed) diagnosed nginx’s port 80 conflict

Episode details: published August 6, 2021 · 24:20 long. Summary written by Self Growth Videos from the episode itself. Business results and any income figures mentioned are NetworkChuck’s own claims, shared for education — they are not typical or guaranteed.

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