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==Control==
[[POSIX]] specifies the [[user interface]] to job control {{endash}} modeled on the Korn shell.<ref>{{man|cu|bg|SUS}}; {{man|cu|fg|SUS}}.</ref>. The commands are typically implemented as [[shell builtin]]s; not separate [[computer program |programs]].
; Start in background
:If a command line ends with {{code|&}}, then the job starts in the background.
; Pause foreground job
:The foreground job can be paused by pressing {{keypress |Ctrl| Z}}. In this state, a job can be resumed in the background via {{code |bg}} or resumed in the foreground via {{code |fg}}.
; Command {{code |fg}} {{anchor| fg}}▼
:Command {{code |fg}} (short for foreground)
▲; Command {{code |fg}}
▲Command {{code |fg}} (short for foreground) causes a background job to move to the foreground; either the job specified or the one most recently added to the background if none specified.
; Command {{code |wait}}
:Command [[wait (command)|<code>wait</code>]] pauses the interactive session until the specified background jobs complete or for all background jobs of the active shell if none specified.<ref>{{cite web | last=Kerrisk| first=Michael |date=Feb 2, 2025 |title=wait(1p) — Linux manual page |website=man7.org |url=https://www.man7.org/linux/man-pages/man1/wait.1p.html |publisher= |access-date=May 13, 2025}}</ref>
; Command {{code |bg}} {{anchor| bg}}▼
:Command {{code |bg}} (short for background) moves the paused foreground job to the background and resumes it.▼
▲; Command {{code |bg}}
▲Command {{code |bg}} (short for background) moves the paused foreground job to the background and resumes it.
; Command {{code |jobs}}
:Command {{code |jobs}} reports information about each background job including ID, command line and running status (stopped or running).
==Signals==
{{Unreferenced section|date=February 2020}}
The [[interprocess communication]] of job control is implemented via [[Unix signal |signal]]s.
Typically, a shell maintains information about background jobs in a job table. When an [[login session |interactive session]] ends (i.e. user [[logout |logs out]]), the shell sends [[signal (computing)|signal]] [[SIGHUP]] to all jobs, and waits for the process groups to exit before terminating itself. Some shells provide a non-POSIX command [[Disown (Unix)|<code>disown</code>]] that removes a job from the job table. The process group becomes an [[orphan process |orphan]]. The shell will not send it SIGHUP, nor wait for it to terminate. This is one technique for enabling a process as a [[daemon (computer software)|daemon]]; owned direclty by the root process [[init]]. The POSIX command [[nohup |{{code |nohup}}]] provides an alternate way to prevent a job from being terminated by the shell.▼
▲Typically, a shell maintains information about background jobs in a job table. When an [[login session |interactive session]] ends (i.e. user [[logout |logs out]]), the shell sends
Suspending the foreground job (via {{keypress |Ctrl |Z}}) sends signal SIGTSTP (terminal stop) to the processes of the group. By default, this signal causes a process to pause so that the shell can resume. However, a process can ignore the signal. A process can also be paused via signal SIGSTOP (stop), which cannot be ignored.
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