What is a daemon or service?
A daemon or service is a program that runs in the background all the time, waiting to do its job without a user watching.
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A daemon (Unix word) or service (Windows and systemd word) is a long running program with no window. It starts at boot, waits for work, and keeps going after you log out. Think of the building caretaker who is always there even when nobody is in the office. Web servers, databases, SSH and cron are all daemons.
On modern Linux, systemd manages services: you start, stop and enable them with systemctl and read their logs with journalctl. Daemon names traditionally end in d, such as sshd or httpd. Writing a small unit file is how you turn your own script into something that restarts automatically after a crash or reboot.
Check before you run this
- Runs with administrator rights. Make sure you understand every line.
systemctl status nginx
sudo systemctl enable --now nginx
journalctl -u nginx -fSee also: What is a process? and What is a log?
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See also
- 0164 systemd services: systemctl and journalctl basics systemd starts and supervises services on most Linux servers. systemctl starts, stops and enables them; journalctl shows their logs. Beginner · Explains an idea · Linux Article Services & systemd 15 Oct 2026
- 0165 Write a systemd service unit for your own app Turn any long-running program into a proper service: create a unit file, run it as an unprivileged user, restart it on failure… Intermediate · Step by step · Linux Article Services & systemd 15 Oct 2026
- 0166 Replace a cron job with a systemd timer A systemd timer runs a service on a schedule like cron, but logs every run to the journal, can catch up missed… Intermediate · Step by step · Linux Article Services & systemd 15 Oct 2026
- 0167 Fix: Job for nginx.service failed because the control process exited with error code systemctl prints this when a service's start command exits with an error. The real reason is in journalctl; for nginx it is… Intermediate · Fixes an error · Linux Article Networking & firewalls · Services & systemd 15 Oct 2026
- 0168 Server health check script: disk, memory and failed units A dependency-free bash script that checks disk and inode usage, available memory, load, failed systemd units and pending reboots, and exits non-zero… Intermediate · Cheat sheet · Linux Script Disks, LVM & filesystems · Services & systemd 15 Oct 2026
- 0255 Build a monitoring stack with Prometheus, node_exporter and Grafana on one Linux server Install Prometheus and node_exporter as systemd services, scrape and query host metrics with PromQL, then add Grafana with a dashboard and an… Intermediate · Guided project · Linux Article Prometheus & Grafana · Services & systemd 15 Oct 2026
Repos in the wild
- systemd: the Linux system and service manager systemd/systemd The source of systemd, the init system and service manager on most Linux distributions, together with journald, networkd, resolved, timers and the systemctl tool. GitHub
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