Linux services are background applications that run without user intervention. They can be enabled, disabled, and modified. Services can be startup or daemon, and their names vary depending on the Linux distribution. The execution level defines the system state, and there are tools available to configure services.
Linux services are applications that run in the background of the Linux operating system, usually without user intervention. Many Linux services are startup services and are started when the system boots, before the user logs in. Linux is free and open source, so there is a lot of variety, and the specific services installed by default vary depending on which Linux distribution is used. Services can be enabled, disabled, managed and even modified by the user.
Some Linux services start, perform a function, and then close. An example is “kudzu,” which detects new or changed hardware. Other examples include “random”, which generates a random number used for security, and “keytable”, which sets the keyboard mappings and system font.
The other type of service is a daemon, which is a service that always runs. Many of these provide various network services, including the following: “httpd” provides an Apache Web server; “inetd”, the Internet superserver daemon, starts TCP/IP (Transmission Control Protocol/Internet Protocol) network services and is responsible for many other network services; “smtp” sends and receives emails; and “nfs” allows for hosting a network file server. These services might have different names depending on the Linux distribution; for example, the Apache service is called “httpd” on some distributions and “apache2” on others.
Another set of applications function as daemon services, which are not network related and provide continuous functionality. Examples include “cron”, which is used to run scheduled tasks; “gpm”, which supports mouse functionality; “apmd”, which provides advanced power management; and “lpd”, the print spooler.
Services run according to an execution level, which defines the state of the system, such as single-user access, multi-user access, shutdown, and restart. The /etc/inittab file sets the default run level and points to files, usually stored in /etc/rc.d/; these rc.d scripts define which services start when a runlevel is entered. These scripts also define the startup priority and shutdown priority for each service, from 0 to 100, to define the order in which services start and shut down.
Some Linux distributions provide a graphical user interface (GUI) for configuring services. If this is not available on a particular distribution, some command line tools should still be available. The “chkconfig” tool can be used to list services, to create or delete services, or to enable or disable services. The “ntsysv” tool provides a simple interface to choose which services should start automatically. All of the tools for configuring Linux services are simply front-ends to the rc.d scripts and advanced users can directly edit these scripts to manage services.
Protect your devices with Threat Protection by NordVPN
