A background process is a computer process that runs "behind the scenes" (i.e. in the background) and without user intervention.[1] Typical tasks for these processes include logging, system monitoring, scheduling,[2] and user notification.[3]
On a Unix system, a background process or job can be further identified as one whose group ID differs from its terminal group ID. This type of process is unable to receive keyboard signals from and typically will not send output to its parent terminal.[4] This more technical definition does not distinguish between whether or not the process can receive user intervention.
Although background processes are typically used for purposes requiring few resources, any process can be run in the background, and even though the process is running in the background, where it can't be seen, it behaves like any other process.[1]
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In this example running on Debian GNU/Linux, 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 an instance of the bash shell. The TPGID header indicates the foreground process group of the listed process, and the PGID is the process' group ID.[5]
PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND
...
1 3537 3537 3537 tty2 1311 Ss 0 0:00 /bin/login --
3537 463 463 3537 tty2 1311 R 1000 0:00 \_ -bash
463 1245 1245 3537 tty2 1311 S 1000 0:00 \_ sleep 300
463 1311 1311 3537 tty2 1311 R+ 1000 0:00 \_ ps axjf
...
From a Unix command line, a background process can be launched using the "&" operator. The bg utility can resume a suspended job, running it in the background. Using the fg utility will associate a background process with its parent terminal, bringing it into the foreground. The jobs utility will list all processes associated with the current terminal and can be used to bring background processes into the foreground.[4][6]
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.[7] These processes typically use minimal system resources and perform tasks which require little to no input from the user. When launched with the daemon function, daemons are disassociated from their parent terminal.[8]
Many newer versions of smartphone & PDA operating systems now include the ability to start background processes. Due to hardware constraints, background processes on mobile operating systems are often restricted to certain tasks or consumption levels. On Android, CPU usage for background processes is bounded at 5 - 10%.[9] Third-party applications on Apple's iOS are limited to a certain set of functions while running in the background.[3] On both iOS and Android, background processes can be killed by the system if they are using too much of the system's memory.[3][9]