bg - run jobs in the background
bg [job_id ...]
If job control is enabled (see the description of set -m in the sh(1)
manpage), the bg utility resumes suspended jobs from the current
environment by running them as background jobs. If the job specified by
job_id is already a running background job, the bg utility has no effect
and will exit successfully.
Using bg to place a job into the background causes its process ID to
become "known in the current shell execution environment", as if it had
been started as an asynchronous list.
The following operand is supported:
job_id Specify the job to be resumed as a background job. If no job_id
operand is given, the most recently suspended job is used. The
format of job_id is described in the entry for job control job
ID in the (sh) manpage.
The output of bg consists of a line in the format:
"[%d] %s\n", <job-number>, <command>
where the fields are as follows:
<job-number> A number that can be used to identify the job to the
wait, fg and kill utilities. Using these utilities, the
job can be identified by prefixing the job number with
<command> The associated command that was given to the shell.
The following exit values are returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
If job control is disabled, the bg utility will exit with an error and no
job will be placed in the background.
A job is generally suspended by typing the SUSP character (<control>Z).
At that point, bg can put the job into the background. This is most
effective when the job is expecting no terminal input and its output has
been redirected to non-terminal files. A background job can be forced to
stop when it has terminal output by issuing the command:
A background job can be stopped with the command:
kill -s stop job ID
The bg utility will not work as expected when it is operating in its own
utility execution environment because that environment will have no
suspended jobs. In the following examples:
... | xargs bg
each bg operates in a different environment and will not share its parent
shell's understanding of jobs. For this reason, bg is generally
implemented as a shell regular built-in.
fg(1), kill(1), jobs(1), sh(1), wait(1).
PPPPaaaaggggeeee 2222 [ Back ]