In Windows NT operating systems, a Windows service is a computer program that operates in the background. It is similar in concept to a Unix daemon. A Windows service must conform to the interface rules and protocols of the Service Control Manager, the component responsible for managing Windows services. It is the Services and Controller app, services.exe, that launches all the services and manages their actions, such as start, end, etc. Windows services can be configured to start when the operating system is started and run in the background as long as Windows is running. Alternatively, they can be started manually or by an event. Windows NT operating systems include numerous services which run in context of three user accounts: System, Network Service and Local Service. These Windows components are often associated with Host Process for Windows Services. Because Windows services operate in the context of their own dedicated user accounts, they can operate when a user is not logged on. Prior to Windows Vista, services installed as an "interactive service" could interact with Windows desktop and show a graphical user interface. In Windows Vista, however, interactive services are deprecated and may not operate properly, as a result of Windows Service hardening.

Administration

Windows administrators can manage services via:

Services snap-in

The Services snap-in, built upon Microsoft Management Console, can connect to the local computer or a remote computer on the network, enabling users to:

Command line

The command-line tool to manage Windows services is sc.exe. It is available for all versions of Windows NT. This utility is included with Windows XP and later and also in ReactOS. The command's scope of management is restricted to the local computer. However, starting with Windows Server 2003, not only can do all that the Services snap-in does, but it can also install and uninstall services. The command duplicates some features of the command. The ReactOS version was developed by Ged Murphy and is licensed under the GPL.

Examples

The following example enumerates the status for active services & drivers. The following example displays the status for the Windows Event log service.

PowerShell

The Microsoft.PowerShell.Management PowerShell module (included with Windows) has several cmdlets which can be used to manage Windows services:

Other management tools

Windows also includes components that can do a subset of what the snap-in, Sc.exe and PowerShell do. The command can start, stop, pause or resume a Windows service. In Windows Vista and later, Windows Task Manager can show a list of installed services and start or stop them. MSConfig can enable or disable (see startup type description above) Windows services.

Installation

Windows services are installed and removed via *.INF setup scripts by SetupAPI; an installed service can be started immediately following its installation, and a running service can be stopped before its deinstallation.

Development

Writing native services

For a program to run as a Windows service, the program needs to be written to handle service start, stop, and pause messages from the Service Control Manager (SCM) through the System Services API. SCM is the Windows component responsible for managing service processes.

Wrapping applications as a service

The Windows Resource Kit for Windows NT 3.51, Windows NT 4.0 and Windows 2000 provides tools to control the use and registration of services: acts as a service wrapper to handle the interface expected of a service (e.g. handle service_start and respond sometime later with service_started or service_failed) and allow any executable or script to be configured as a service. allows new services to be installed, started, stopped and uninstalled.