Bash job control lets you pause a running command, continue it in the background or foreground, inspect its state, wait for completion, and decide what happens when the shell exits. Add & to launch a batch-like command asynchronously, press Ctrl-Z to suspend a foreground command, then use bg or fg with the job number shown by jobs. For work that must survive logout, redirect its input and output and use disown (or a service/session manager when appropriate).
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What Bash job control does
The GNU Bash Reference Manual defines job control as the ability to selectively stop (suspend) processes and continue (resume) them later. Bash treats each pipeline as one job and keeps an entry for it in a per-shell job table. A job may contain several processes, but Bash gives the pipeline one job number so you can manage it as a unit.
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Interactive job control is normally enabled in an interactive Bash session. A non-interactive shell, such as one running a script, generally does not provide the same interactive job-management behavior unless it is explicitly configured and attached to a suitable terminal.
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Foreground and background execution compared
| Aspect | Foreground job | Background job |
|---|---|---|
| Shell prompt | Bash waits for the command and does not give you the prompt until it exits or is stopped. | Bash returns the prompt immediately after starting the asynchronous job. |
| Terminal input | Can normally read from the controlling terminal. | Cannot normally read from the controlling terminal; a read usually causes SIGTTIN and stops the process. |
| Keyboard signals | The terminal sends signals such as SIGINT and SIGTSTP to the foreground process group. |
It is in another process group and is immune to those keyboard-generated signals. |
| Job table | Tracked by Bash while it runs and after it stops, subject to normal job-table cleanup. | Tracked by Bash until it finishes, is removed, or is disowned. |
| Shell exit | A running or stopped job can cause an exit warning; shell hangup behavior depends on job state and disown settings. | A job still associated with Bash can receive SIGHUP when the shell exits; disown -h prevents Bash from sending that hangup. |
| Typical use | Interactive programs, commands needing terminal input, and tasks whose output you want to watch directly. | Long, batch-like commands such as builds, downloads, conversions, and log processing. |
Putting a command in the background does not automatically detach it from the terminal. Its standard input, standard output, and standard error still point wherever the command inherited them unless you redirect them explicitly.
Start a command in the background with &
Append an ampersand to the command or pipeline:
long_command >output.log 2>&1 &The redirections send normal output and error output to output.log, while & asks Bash to run the command asynchronously. Because the command is no longer occupying the foreground, Bash prints a job number and a process ID, for example:
[1] 25647The number and PID are examples; your session assigns different values. The bracketed value is the Bash job number, while the second value is a process ID. A pipeline such as producer | consumer is one Bash job even though it contains multiple processes.
Choose redirections for the kind of job
- For a command that only produces output, redirect at least standard output if terminal messages would interfere with your interactive work.
- Redirect standard error separately when you need to distinguish diagnostics, for example
command >out.log 2>error.log &. - Redirect both streams to one file with
>out.log 2>&1, as in the example above. - If the program might read input, provide an input file such as
<input.txt. Otherwise a background read from the terminal can stop it withSIGTTIN.
Use an explicit command such as long_command <input.txt >output.log 2>&1 & when you want a genuinely batch-like background task.
List jobs and understand the job numbers
Run jobs to display active jobs known to the current Bash process:
jobsFor process IDs and more detail, use:
jobs -lA typical listing might show a running, stopped, or completed state. The exact text varies with the command and Bash version, but the leading number is the jobspec you use with other job-control builtins.
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%1selects job 1.%%and%+select the current job, normally the one Bash considers most recently active.%-selects the previous job.- A unique command-name prefix can identify a job, such as
%longfor a job whose command begins withlong. - A unique substring can also identify a job with
%?text, wheretextoccurs in the command line.
If a prefix or substring matches more than one job, Bash reports an ambiguous jobspec. Run jobs and use the numeric form to remove uncertainty.
Jobs are local to a shell
The job table belongs to the Bash session that started the command. Opening another terminal, connecting through a second SSH session, or running a command under a different shell gives you a different job table. A PID visible through a system process tool is not automatically a jobspec in your current shell.
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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 foreground job and returns the prompt. The manual describes this as typing the suspend character to stop the process and return control to Bash.
At that point the job is stopped, not completed. It remains in the job table and can be resumed without restarting it. Bash normally prints a message identifying the stopped job, such as [1]+ Stopped.
Continue the stopped job in the background
- Press
Ctrl-Zwhile the command is in the foreground. - Check the assigned number with
jobsif necessary. - Resume it asynchronously with
bg %1, replacing%1with the actual jobspec.
bg %1bg resumes each specified stopped job in the background. With no jobspec, bg uses the current job:
bgA resumed background job can continue writing to the terminal unless its output is redirected. Resuming it in the background does not change its inherited file descriptors.
Bring a job back to the foreground
Use fg with the job number:
fg %1fg resumes a stopped job if necessary, makes its process group the terminal’s foreground group, and waits for it as the foreground command. With no jobspec, it selects the current job. The return status of fg is the status of the foreground command, so you can inspect it with echo $? immediately afterward.
A concise handoff is therefore:
# foreground command is running
# press Ctrl-Z
bg %1 # continue without occupying the prompt
fg %1 # take it back over the terminal laterWait for a background job and collect its status
Use wait when a script or interactive session must pause until a job finishes:
wait %1wait accepts jobspecs or process IDs. With several identifiers, it waits for them and returns the status of the last identifier it processes. To wait for a process to terminate rather than merely undergo a status change, Bash provides wait -f when job control is enabled:
wait -f %1After waiting, inspect the exit status immediately:
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wait %1
status=$?
printf 'job exit status: %sn' "$status"Waiting is different from bringing a job forward. wait does not attach the terminal to the job and does not make an interactive program usable; it only waits for the requested status condition.
Stop or signal a job with kill
When job control is active, Bash’s kill builtin can address a jobspec:
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kill %1That sends the default termination signal. Specify another signal when appropriate:
kill -STOP %1
kill -CONT %1
kill -TERM %1SIGSTOP unconditionally stops a process and cannot be caught or ignored; SIGCONT continues a stopped process. A normal termination request uses SIGTERM, giving the program an opportunity to clean up. Use a PID instead when you are outside the shell’s jobs table or when a specific process in a larger job must be addressed.
To force a background process to stop because it is misbehaving or consuming resources, send SIGSTOP with the Bash builtin or an external signal tool as appropriate. Keyboard-generated signals from your terminal will not reach a background process group.
Keep work from being tied to a shell with disown
disown changes Bash’s bookkeeping; it does not create a daemon and does not redirect input or output. First start the command with suitable redirections, then disown it if you do not want this shell to manage it:
long_command </dev/null >output.log 2>&1 &
disown %1After disown %1, Bash removes the job from its active table. jobs will no longer list it, and you cannot use that shell’s jobspec to run fg, bg, or wait for it.
Protect a job from Bash’s hangup signal while keeping it listed
Use the -h option to mark a job so Bash does not send it SIGHUP when the shell exits, while leaving the job in the table:
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disown -h %1The form disown -h is useful when you still want to inspect or manage the job during the current session. It does not alter the program’s standard input, output, or error streams. A program that later tries to read the terminal can still be stopped, and output can still appear in the terminal unless redirected.
Control the scope of disown
In Bash’s syntax, disown [-ar] [-h] [id ...] accepts options and job identifiers. With no identifier, it acts on the current job. The -a option applies to all jobs; -r limits the operation to running jobs. Use these broader forms deliberately because they can affect more jobs than the one you intended.
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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsFor an interactive session that must survive a logout reliably, a terminal multiplexer or a service manager is usually more appropriate than treating disown as a full process supervisor. Job control only changes Bash’s relationship with the process; it does not provide restart policies, logging rotation, dependency ordering, or monitoring.
How the terminal and process groups explain job-control behavior
The terminal maintains one foreground process group. When a foreground pipeline runs, the processes in that group receive keyboard-generated signals. Bash temporarily manages the terminal for the job and waits for the foreground command; Bash itself is not in that same terminal process group while it is waiting, so it does not receive those keyboard-generated signals intended for the command.
Background processes belong to a different process group. A background process that attempts to read from the controlling terminal normally receives SIGTTIN, which stops it. This is why an interactive program that needs input should generally remain in the foreground or receive input from a redirected file.
Writes are normally allowed, so a background job may print over your prompt. If the terminal’s tostop setting is enabled, however, a background write can cause SIGTTOU and stop the writer. Redirecting output avoids both confusing terminal interleaving and many write-related surprises.
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Commands and options at a glance
| Command | Purpose | Important behavior |
|---|---|---|
jobs [-lnprs] |
List active jobs. | -l includes process IDs; other flags select listing formats and states. |
jobs -x command [arguments] |
Run a command after substituting process-group IDs for jobspecs in its arguments. | Useful when a command expects numeric process-group IDs rather than Bash’s % notation. |
bg [jobspec ...] |
Continue stopped jobs in the background. | No jobspec means the current job. |
fg [jobspec] |
Continue a job in the foreground. | No jobspec means the current job; its status is the foreground command’s status. |
wait [jobspec|pid ...] |
Wait for jobs or processes. | Returns the status of the last identifier; -f waits for termination rather than a status change when job control is enabled. |
kill [options] jobspec|pid |
Send a signal. | Jobspec use requires an active Bash job table; signal names such as -STOP, -CONT, and -TERM select the action. |
disown [-ar] [-h] [id ...] |
Remove jobs from Bash or prevent a hangup signal. | -h keeps the job listed but suppresses Bash’s SIGHUP; without -h, the job is removed. |
suspend |
Pause the shell itself until SIGCONT. |
A login shell or shell without job control cannot normally be suspended; suspend -f forces it. |
Reliable workflows for common tasks
Run a long batch command and return to the prompt
- Decide where standard input, output, and error should go.
- Launch the command asynchronously:
long_command </dev/null >output.log 2>&1 &. - Record the job number and PID printed by Bash.
- Use
jobs -lto inspect its state later. - Run
wait %1when you need the completion status.
Pause an interactive command, do something else, then resume it
- Press
Ctrl-Zto stop the foreground command. - Run a short command or inspect the job with
jobs. - Use
bg %1to let the stopped command continue without the terminal. - Use
fg %1when you need to interact with it again.
Cancel a background job
- Run
jobs -land identify the correct jobspec. - Send a graceful termination request with
kill %1orkill -TERM %1. - Check the result with
jobs. - If the process remains and you have confirmed it is safe to force it, use a stronger signal such as
kill -KILL %1; this gives the program no opportunity to clean up.
Troubleshooting job-control errors
“fg: no such job” or “bg: %1: no such job”
The jobspec may belong to another shell, the job may already have exited, or the number may be wrong. Run jobs in the same shell that started the command. Use the displayed number, %+, or %- rather than guessing.
The background command stopped unexpectedly
Check jobs for a stopped status. The most common cause is a read from the controlling terminal, which triggers SIGTTIN. Restart or resume the command with input redirected from a file or another intended source. If tostop is enabled, a background write may instead have triggered SIGTTOU; redirect output to a file or pipe.
Output is mixed into the prompt
Background status does not silence a program. Redirect standard output and standard error when launching it, or send them through a logging pipeline. Redirecting after the command has started generally requires restarting it with the desired file descriptors.
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The job disappeared after the shell closed
If you used disown without -h, Bash removed the job from its table, but that alone does not guarantee survival. If the shell exits while it still owns a job, Bash may send SIGHUP. Use explicit input and output redirections and disown -h when you need to prevent Bash’s hangup signal. For durable services, use a supervisor designed for that purpose.
Bash warns about jobs when exiting
Bash can warn about stopped jobs on shell exit. With the checkjobs option enabled, it can also warn about running jobs and list their statuses. Treat the warning as a prompt to inspect jobs, then bring a job forward, terminate it, or disown it intentionally rather than closing the terminal blindly.
Ctrl-C does not stop the background process
That behavior is expected: keyboard-generated signals go to the terminal’s foreground process group, not to a background group. Use kill %jobspec or a PID to signal the background process.
Limits of job control
Job control is a shell-and-terminal feature, not a replacement for process supervision. It is ideal for deciding whether an interactive command currently owns your terminal and for moving work between stopped, foreground, and background states. It does not restart failed programs, preserve a process across every kind of session termination, provide service dependencies, or guarantee that a program designed for terminal interaction will work unattended.
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For a command that simply needs time to finish, launch it with complete redirections, inspect it with jobs -l, and use wait when its result matters. For an interactive command, keep it in the foreground whenever it needs keyboard input, and use Ctrl-Z, bg, and fg as temporary state changes rather than as a substitute for configuring the program’s input and output.
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