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Bash job control lets you pause a running command, resume it in the background or foreground, inspect its job number, wait for completion, and control what happens when the shell exits. Start a batch-style command asynchronously by appending &, inspect it with jobs, suspend a foreground command with Ctrl+Z, then use bg or fg with the displayed jobspec.
long_command >output.log 2>&1 &
jobs -l
# Press Ctrl-Z on a foreground command, then:
bg %1
fg %1
wait %1What Bash job control does
Job control is Bash’s mechanism for selectively stopping (suspending) processes and resuming them later. Bash associates a job with each pipeline and keeps those jobs in a job table. The jobs builtin displays the jobs Bash currently knows about, usually with a small job number such as 1.
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A job can be a single command or a pipeline. For example, generate | sort | less is one Bash job even though it contains several processes. Job control operates on that pipeline as a unit when you use a jobspec such as %1.
Foreground and background are not merely labels in the prompt. Bash places the active terminal process group in the terminal’s foreground process group. Processes in that group can receive keyboard-generated signals such as SIGINT when you press Ctrl+C. A background process is in another process group: it cannot normally read from the controlling terminal, and a read normally causes SIGTTIN, suspending it. If the terminal’s tostop setting is enabled, a background write can cause SIGTTOU.
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Foreground and background execution compared
| Behavior | Foreground job | Background job |
|---|---|---|
| Shell prompt | Bash waits for the command and does not give you a prompt until it stops or exits. | Bash returns the prompt immediately after starting the asynchronous job. |
| Terminal input | Can read from the controlling terminal. | Cannot normally read from the controlling terminal; a read can trigger SIGTTIN. |
| Keyboard signals | Receives terminal-generated signals such as SIGINT. |
Is in a different process group and is not targeted by those keyboard-generated signals. |
| Job table | Tracked as the current job while it runs. | Listed by jobs while Bash keeps it active. |
| Best fit | Interactive programs that need your input. | Batch-like work that can run without terminal interaction. |
| Shell exit | A stopped or running job can produce an exit warning; SIGHUP handling depends on Bash’s job bookkeeping. | Use disown or disown -h when you need to change Bash’s tracking or SIGHUP behavior. |
When Bash is waiting for a foreground command, Bash itself is not in the terminal’s foreground process group and therefore does not receive the keyboard-generated signals intended for that command. To stop a background process deliberately, send it SIGSTOP with Bash’s kill builtin or an appropriate external signal tool.
Run a command in the background with &
Append & to a command to make it asynchronous. Bash starts the command, prints a job number and process ID, and immediately displays a new prompt.
long_command >output.log 2>&1 &The redirections in this example write standard output to output.log and merge standard error into the same file. Redirecting output is important for a command that should run unattended; otherwise its output can appear in your terminal while you type. The exact job number and PID vary by shell session. A typical startup message looks like this:
[1] 25647Here, 1 is Bash’s job number and 25647 is an example process ID. Do not assume either value will be the same in another session.
Choose background candidates carefully
- Use the background for batch-like commands that do not need keyboard input.
- Keep an interactive program in the foreground when it expects terminal input.
- Redirect output and, when necessary, input explicitly before starting a long-running job.
- Remember that a pipeline remains one Bash job even though several processes may be running inside it.
List jobs and identify the right jobspec
Run jobs to see active jobs:
jobsFor process IDs as well as job states, use:
jobs -lBash displays a job number, a state such as running or stopped, and the command text. The -l option adds process IDs. A jobspec begins with %:
| Jobspec | Meaning |
|---|---|
%1 |
Job number 1. |
%% or %+ |
The current job. |
%- |
The previous job. |
%string |
The job whose command begins with the supplied, unique string. |
%?string |
The job whose command contains the supplied, unique string. |
Prefix and substring forms must identify one job unambiguously. If you are unsure which job is current, run jobs and use the number it prints, %+, or %-.
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Suspend a foreground command with Ctrl+Z
While a foreground process is running, press the terminal’s suspend character, typically Ctrl+Z. Bash stops the process and returns control to the shell. The command is not finished; it is in a stopped state and remains in the job table.
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interactive_or_long_command
# Press Ctrl-Z
[1]+ Stopped interactive_or_long_commandThe exact status line depends on the command and session. Once Bash displays a prompt, decide whether to continue the stopped job in the background or return it to the foreground.
Resume a stopped job in the background with bg
Use bg followed by a jobspec:
bg %1bg [jobspec ...] resumes each specified stopped job in the background. With no jobspec, Bash uses the current job:
bgAfter bg, the process continues without occupying the terminal’s foreground process group, and Bash gives you a prompt. It can still produce output unless you redirected it when launching the command.
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Use fg when a job needs terminal interaction or when you want to watch it directly:
fg %1fg [jobspec] resumes the selected job in the foreground and makes it the current job. With no jobspec, it selects the current job. The return status of fg is the status of the foreground command, so a failed command can make the fg invocation return a failure status.
If the process was stopped, fg continues it before handing terminal control to it. If it was already running in the background, fg moves it into the foreground process group.
A complete stop, resume, and wait workflow
- Start or run a command. For unattended work, launch it with output redirection and
&:long_command >output.log 2>&1 & - Record the job identity. Note the job number Bash prints, then confirm it with
jobs -l. - Suspend interactive work when needed. For a foreground command, press Ctrl+Z. Bash returns a prompt and marks the job stopped.
- Continue without the terminal. Run
bg %n, replacingnwith the number shown byjobs. - Inspect state. Run
jobs -lagain. A running job may finish and disappear from the active job table after Bash reports its completion. - Return terminal control. Run
fg %nwhen the command needs input or you want it attached to the terminal again. - Wait for a result. Run
wait %nto wait for that job and receive its completion status.
Wait for completion and retrieve status
The wait builtin accepts jobspecs or process IDs:
wait %1
wait 25647When given several identifiers, wait waits for them and returns the status of the last identifier. With job control enabled, wait -f waits for termination rather than merely waiting for a status change:
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wait -f %1Waiting is useful in scripts and at an interactive prompt when a background job must finish before you inspect its output or start a dependent step. If the job has already exited and Bash has discarded it from the active table, use the process or job information that is still available in your shell’s output and check the command’s own log or status handling.
Control or stop jobs with kill
When job control is active, Bash’s kill builtin can target a jobspec:
kill %1To force a background process into the stopped state, send SIGSTOP explicitly:
kill -STOP %1A stopped job can later be resumed with bg %1 or fg %1. Use the least forceful signal that accomplishes your goal, and verify the target with jobs -l before signaling it.
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disown changes Bash’s bookkeeping for a job; it does not create a new session and does not redirect a program’s standard input or output. Set up redirections when launching the command if it must run without an interactive terminal.
Remove the job from Bash’s table
disown %1This removes job 1 from Bash’s active job table. Once removed, Bash no longer manages that job as an active job, so jobs, fg, and bg cannot select it through that table.
Keep it listed but prevent Bash from sending SIGHUP
disown -h %1disown -h leaves the job listed but marks it so Bash will not send it SIGHUP when the shell sends hangup signals during exit. This changes Bash’s treatment of the job; it does not guarantee that the application is independent of the terminal or that it will never receive another signal.
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Scope options
The general form is disown [-ar] [-h] [id ...]. With no identifier, Bash operates on the current job. The -a option applies the operation to all jobs, while -r limits it to running jobs. Choose the scope deliberately, especially in a shell that has several active jobs.
What happens to terminal input and signals
The terminal maintains one foreground process group. Members of that group receive keyboard-generated signals such as the interrupt signal produced by Ctrl+C. A background process is in another process group, so those keyboard signals do not target it merely because it is running in the same shell.
Background jobs are prohibited from reading the controlling terminal. A program that tries to read from standard input while in the background normally receives SIGTTIN and stops. This is why a command that prompts for a password, accepts menu choices, or otherwise expects live terminal input should generally stay in the foreground or receive input from a redirected file.
Background output is different: a job can write to the terminal unless output is redirected. If stty tostop is enabled, a background write can instead cause SIGTTOU and stop the process. Redirect noisy or unattended commands to a file when practical.
Shell-exit warnings and stopped jobs
On shell exit, Bash can warn about stopped jobs. When the checkjobs shell option is enabled, Bash can also warn about running jobs and list their statuses. These warnings are a reminder to inspect the job table before closing the shell.
Before exiting, run:
jobs -lFor a job you want to finish under Bash’s supervision, use wait %n. For a job that should not receive Bash’s hangup treatment, use disown -h %n, and ensure its input and output do not depend on the terminal. If a job is stopped unintentionally, resume it with bg %n or bring it forward with fg %n before deciding whether to exit.
Troubleshooting common job-control errors
“fg: %1: no such job” or an invalid jobspec
The number may belong to an earlier job that has finished, or the current shell may have a different job table. Run jobs, copy an active number, and retry. You can also use %+ for the current job or %- for the previous job.
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The background command stops immediately
Check whether it is trying to read from the terminal. A background read normally triggers SIGTTIN. Keep the command in the foreground or redirect standard input explicitly, then resume it with bg %n if appropriate.
The command’s output appears mixed with your typing
Background status does not suppress output. Redirect standard output and standard error when launching the command:
long_command >output.log 2>&1 &If the job is already running, bring it forward with fg %n and restart it with suitable redirections when that is safe for the program.
disown did not make the program independent
disown only changes Bash’s job bookkeeping and SIGHUP behavior. It does not detach standard input, standard output, or standard error from the terminal. Start the command with explicit redirections and choose a program design that does not require interactive input.
Ctrl+Z did not finish the command
Ctrl+Z is the suspend character. It stops the foreground job and returns a prompt; it does not terminate the process. Use bg %n or fg %n to continue it, or use kill %n when termination is what you intend.
A pipeline seems to have several process IDs
That is expected. Bash treats the pipeline as one job for job-control commands, while each component can have its own process ID. Use the job number with fg, bg, wait, or kill; use jobs -l when you need the individual IDs.
Quick Recap
Useful command reference
| Command | Purpose | Important behavior |
|---|---|---|
jobs [-lnprs] [jobspec] |
List active jobs. | -l includes process IDs; job numbers and states come from the current shell. |
jobs -x command [arguments] |
Run a command after replacing jobspecs with process-group IDs. | Useful when another command expects process-group IDs rather than Bash jobspec syntax. |
bg [jobspec ...] |
Resume stopped jobs in the background. | No jobspec means the current job. |
fg [jobspec] |
Resume or move a job to the foreground. | No jobspec means the current job; its status is the foreground command’s status. |
wait [jobspec or PID] |
Wait for completion or a state change. | Returns the status of the last identifier; wait -f waits for termination when job control is enabled. |
kill [signal] jobspec |
Send a signal to a job. | Use SIGSTOP when you specifically need to force a running background process to stop. |
disown [-ar] [-h] [id ...] |
Change Bash’s tracking and hangup treatment. | Without -h, the selected job is removed; -h keeps it listed but prevents Bash from sending it SIGHUP. |
suspend |
Pause the shell until SIGCONT. |
A login shell or shell without job control cannot normally be suspended; suspend -f forces it. |
Practical decision guide
- Need the prompt immediately? Append
&, then inspect the job withjobs -l. - Need to pause what is currently running? Press Ctrl+Z.
- Want it to continue without occupying the terminal? Run
bg %n. - Need to interact with it again? Run
fg %n. - Need to know when it finishes? Run
wait %norwait -f %nwhen termination, rather than any state change, is required. - Need to stop it deliberately? Verify the target with
jobs -l, then usekill %norkill -STOP %nfor a forced suspension. - Closing the shell? Check
jobs -l, redirect I/O for unattended work, and usedisownordisown -honly when their specific bookkeeping and SIGHUP effects match your goal.
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