Background process

{{Main article|Windows service}}

In Windows NT family of operating systems, a Windows service is a dedicated background process.{{cite web|title=Services overview|url=https://technet.microsoft.com/en-us/library/cc783643%28v=ws.10%29.aspx|work=Microsoft TechNet|publisher=Microsoft|accessdate=29 March 2013}} A Windows service must conform to the interface rules and protocols of the Service Control Manager, the component responsible for managing Windows services.{{Cite web |url=http://msdn2.microsoft.com/en-us/library/ms685141.aspx |title=Services |work=Microsoft Developer Network |publisher=Microsoft |accessdate=29 March 2013}}

Windows services can be configured to start when the operating system starts, and to run in the background as long as Windows runs. 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: svchost.exe. Since Windows services operate in the context of their own dedicated user accounts, they can operate when a user is not logged on.

Before Windows Vista, services installed as "interactive services" could interact with Windows desktop and show a graphical user interface. With Windows Vista, however, interactive services became deprecated and ceased operating properly, as a result of Windows Service Hardening.{{cite web|title=New Elevation PowerToys for Windows Vista|url=https://technet.microsoft.com/en-us/magazine/2008.06.elevation.aspx|work=TechNet Magazine|publisher=Microsoft|accessdate=21 June 2013|date=June 2008|quote=The service CmdAsSystem is configured as interactive whose support is being deprecated. The service may not function properly. The problem is that this script tries to create and start an interactive service. Interactive services will not function correctly due to Session 0 Isolation in Windows Vista.}}{{cite web|title=Services in Windows|url=http://msdn.microsoft.com/en-us/windows/hardware/gg463428.aspx|work=MSDN|publisher=Microsoft|accessdate=21 June 2013|date=18 October 2010}}

The three principal means of managing Windows services are:

1. Services snap-in for Microsoft Management Console
2. sc.exe
3. Windows PowerShell

{{Main article|Daemon (computing)}}

A daemon is a type of background process designed to run continually in the background, waiting for event(s) to occur or condition(s) to be met.{{cite book|url=http://catb.org/~esr/jargon/html/D/daemon.html |title=The Jargon File, version 4.4.8, "daemon" |author=Eric S. Raymond |date=1 October 2004 |accessdate=10 November 2010 |archiveurl=https://web.archive.org/web/20101103102331/http://catb.org/~esr/jargon/html/D/daemon.html |archivedate=3 November 2010 |url-status=live }} When launched with the daemon function, daemons are disassociated from their parent terminal.{{cite book|url=http://libslack.org/daemon/manpages/daemon.1.html|title=Linux User's Manual, "daemon"|author=raf|date=12 June 2010|accessdate=10 November 2010|archiveurl= https://web.archive.org/web/20101021032110/http://libslack.org/daemon/manpages/daemon.1.html|archivedate= 21 October 2010|url-status=live}}

{{main article|Job control (Unix)}}

From a Unix command line, a background process can be launched using the "&" operator. The bg command can resume a suspended job (sending SIGCONT), running it in the background. Using the fg command will also reconnect standard input its parent terminal, bringing it into the foreground. The jobs command will list all processes associated with the current terminal and can be used to bring background processes into the foreground.{{cite web|url=http://www.astro.ku.dk/comp-phys/tutorials/background.shtml|title=Background Processes in Unix/Linux|author=Åke Nordlund|date=7 February 2007|accessdate=10 November 2010|archive-url=https://web.archive.org/web/20120213174734/http://www.astro.ku.dk/comp-phys/tutorials/background.shtml|archive-date=13 February 2012|url-status=dead}}

When a login session ends, via explicit logout or network disconnection, all processes, including background processes, will by default be terminated, to prevent them from becoming orphan processes. Concretely, when the user exits the launching shell process, as part of shutdown it sends a hangup signal (SIGHUP) to all its jobs, to terminate all the processes in the corresponding process group. To have processes continue to run, one can either not end the session, or end the session without terminating the processes. A terminal multiplexer can be used to leave a session running but detach a virtual terminal from it, leaving processes running as child processes of the session; the user can then reattach session later. Or, termination can be prevented by either starting the process via the nohup command (telling the process to ignore SIGHUP), or by subsequently running disown with the job id, which either removes the job from the job list entirely, or simply prevents SIGHUP from being sent. In the latter case when the session ends, the child processes are not terminated, either because they are not sent SIGHUP or because they ignore it, and thus become orphan processes, which are then adopted by the init process (the kernel sets the init process as their parent), and they continue running without a session, now called daemons.

In this example running on Unix, the sleep utility was launched into the background. Afterward, the ps tool was run in the foreground, where it output the below text. Both were launched from the shell.{{cite web |url=http://pubs.opengroup.org/onlinepubs/7999959899/utilities/ps.html|title=POSIX "ps"|work=IEEE Std 1003.1, 2004 Edition}}

PID TT STAT TIME COMMAND

54659 10 S 0:00.06 su (zsh)

54703 10 IN 0:00.00 - sleep 1000

54852 10 R+ 0:00.00 - ps -U botty -axd

Many newer versions of smartphone and PDA operating systems now include the ability to start background processes. Due to hardware limits, background processes on mobile operating systems are often restricted to certain tasks or consumption levels. On Android, CPU use for background processes may be bounded at 5–10%.{{cite web|url=https://gizmodo.com/5527407/giz-explains-how-multitasking-works-on-a-phone|title=Giz Explains: How Multitasking Works on a Phone|author=Matt Buchanan|date=2010-04-29|publisher=Gizmodo|accessdate=14 November 2010|archiveurl= https://web.archive.org/web/20101017123040/http://gizmodo.com/5527407/giz-explains-how-multitasking-works-on-a-phone|archivedate=17 October 2010|url-status=live}} Applications on Apple's iOS are limited to a subset of functions while running in the background. On both iOS and Android, background processes can be killed by the system if they are using too much memory.

• Batch processing
• Computer multitasking
• Process group

{{reflist|30em}}

{{DEFAULTSORT:Background Process}}

Category:Process (computing)