Difference between revisions of "Daemons"

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Revision as of 13:22, 8 February 2013

A daemon is a program that runs as a "background" process (without a terminal or user interface), commonly waiting for events to occur and offering services. A good example is a web server that waits for a request to deliver a page, or a ssh server waiting for someone trying to log in. While these are full featured applications, there are daemons whose work is not that visible. Daemons are for tasks like writing messages into a log file (e.g. syslog, metalog) or keeping your system time accurate (e.g. ntpd). For more information see man 7 daemon.

Note: The word daemon is sometimes used for a class of programs that are started at boot but have no process which remains in memory. They are called daemons simply because they utilize the same startup/shutdown framework (e.g. systemd service files of Type oneshot) used to start traditional daemons. For example, the service files for alsa-store and alsa-restore provide persistent configuration support but do not start additional background processes to service requests or respond to events.

From the user's perspective the distinction is typically not significant unless the user tries to look for the "daemon" in a process list.

Managing daemons

In Arch Linux, daemons are managed by systemd. The systemctl command is the user interface used to manage them. It reads <service>.service files that contain information about how and when to start the associated daemon. Service files are stored in /{etc,usr/lib,run}/systemd/system. See systemd#Using units for complete information about using systemctl to manage daemons.

Starting on boot

To add or remove services to be started at boot-time, use systemctl enable|disable <service_name>

Starting manually

To start or stop services at runtime, use systemctl start|stop <service_name>.

Restarting

To restart services, use systemctl restart <service_name>.

Status reporting

To report the current status of a service, use systemctl status <service_name>.

List of daemons

See Daemons List for a list of daemons with the name of the service and legacy rc.d script.

See also