Windows service

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:
 The Services snap-in (found under Administrative Tools in Windows Control Panel)
 Sc.exe
 Windows PowerShell

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:
 view a list of installed services along with service name, descriptions and configuration
 start, stop, pause or restart services 
 specify service parameters when applicable
 change the startup type. Acceptable startup types include:
Automatic: The service starts at system startup.
Automatic (Delayed): The service starts a short while after the system has finished starting up. This option was introduced in Windows Vista in an attempt to reduce the boot-to-desktop time. However, not all services support delayed start.
Manual: The service starts only when explicitly summoned.
Disabled: The service is disabled. It will not run.
 change the user account context in which the service operates
 configure recovery actions that should be taken if a service fails
 inspect service dependencies, discovering which services or device drivers depend on a given service or upon which services or device drivers a given service depends
 export the list of services as a text file or as a CSV file

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 sc command's scope of management is restricted to the local computer. However, starting with Windows Server 2003, not only can sc do all that the Services snap-in does, but it can also install and uninstall services.

The sc command duplicates some features of the net 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.
C:\>sc query

The following example displays the status for the Windows Event log service.
C:\>sc query eventlog

PowerShell
The Microsoft.PowerShell.Management PowerShell module (included with Windows) has several cmdlets which can be used to manage Windows services:
 Get-Service
 New-Service
 Restart-Service
 Resume-Service
 Set-Service
 Start-Service
 Stop-Service
 Suspend-Service

Other management tools
Windows also includes components that can do a subset of what the snap-in, Sc.exe and PowerShell do. The net 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: SrvAny.exe 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. Sc.exe allows new services to be installed, started, stopped and uninstalled.

See also
 Windows services
 
 Windows Service Hardening
 svchost.exe

 Concept
 Background process
 Daemon (computing)
 DOS Protected Mode Services
 Terminate-and-stay-resident program
 Device driver
 Operating system service management
 Service Control Manager
 Service Management Facility
 Service wrapper

References

Further reading
 
 David B. Probert, Windows Service Processes

External links

 Windows Sysinternals: Autoruns for Windows v13.4 – An extremely detailed query of services
 Service Management With Windows Sc From Command Line – Windows Service Management Tutorial
 Windows Service Manager Tray

 
Process (computing)