CHECKING BACKGROUND JOBS

This document explains the jobs command, which is part of Job control in UNIX and UNIX LIKE systems.

The jobs command is used to check the jobs that are currently running in the background of the current shell.

In comparison to Windows,
jobs is similar to checking the programs that are running in the background, minimized and not visible in the foreground, akin to the taskbar.

🔵 NOTE

In UNIX, a Job refers to a collection of Processes. The PID of a job refers to the Process Group ID.

🔵 NOTE

This was tested using zsh on MacOS, Sonoma.
zsh has extended features, and more information can be found in man zshbuiltins.

🔵 NOTE

This document is a translation of the jobs description from The Open Group Base Specifications Issue 7, provided by the official UNIX group, THE Open GROUP, and briefly explains the parts that users need to know.

SYNOPSIS

• [ ] (brackets) are optional.
• | (pipe) indicates that one of several options can be chosen.
• ... (three dots) indicates that multiple arguments can be specified.

jobs [-l| -p][job_id...]

OPTIONS

• -l
  (lowercase L) provides more information about each listed job. This information includes the job number, current job, process group ID, state, and the command that formed the job.

• -p
  displays only the process ID of the process group leader for the selected job.

OPERANDS

• job_id
  specifies the job for which to display the status. If no job_id is specified, status information for all jobs will be displayed. The format of job_id is described in XBD Job Control Job ID.

STDOUT

If the -p option is specified,
the output consists of one line for each process ID.

"%d\n", <process ID>

If the -l option is not specified,
the output consists of a series of lines in the following format.

"[%d] %c %s %s\n", <job-number>, <current>, <state>, <command>

Where the fields are as follows:

• <job-number>

  • A number that can be used to identify the process group for the wait, fg, bg, and kill utilities.
  • These utilities can identify a job by prefixing the job number with %.

• <current>

  • The character + identifies the job that will be used as the default for the fg or bg utilities.
    This job can also be specified using job_id %+ or "%%".
  • The character - identifies the job that will become the default when the current default job terminates.
    This job can also be specified using job_id %-.
  • For other jobs, this field is a space.
  • At most one job can be identified with +, and at most one job can be identified with -.
  • If any job is suspended, the current job must be a suspended job.
  • If at least two jobs are suspended, the previous job must also be a suspended job.

• <state>
  One of the following strings (in POSIX locale):

  • Running
    Indicates that the job has not been stopped by a signal and has not terminated.
  • Done
    Indicates that the job has completed and returned an exit status of 0.
  • Done(code)
    Indicates that the job has completed normally and terminated with the specified non-zero exit status, code.
  • Stopped
    Indicates that the job has been stopped by the SIGTSTP signal.
  • Stopped (SIGTSTP)
    Indicates that the job has been stopped by the SIGTSTP signal.
  • Stopped (SIGSTOP)
    Indicates that the job has been stopped by the SIGSTOP signal.
  • Stopped (SIGTTIN)
    Indicates that the job has been stopped by the SIGTTIN signal.
  • Stopped (SIGTTOU)
    Indicates that the job has been stopped by the SIGTTOU signal.

• <command>

  • The relevant command provided to the shell.

If the -l option is specified,
a field containing the process group ID is inserted before the <state> field.
Additionally, more processes within the process group may be output on separate lines, using only the process ID and <command> fields.

EXAMPLE

First, enter a command in the shell to create a simple job.

sleep 100 &

This command runs sleep, which waits for 10 minutes and then terminates, in the background using & (ampersand).

🔵 NOTE

& (ampersand) is the command to run a process in the background in the current session.

The result of running the jobs command with no options is as follows.

Command input

jobs

Output

[1] + 12345 Running sleep $((60 * 10)) &

The result of running the jobs command using zsh is as follows.
In zsh, when a job terminates, Done is displayed.