This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       A  job  is  generally  suspended by typing the SUSP character (<control>‐Z on most systems); see the Base
       Definitions volume of POSIX.1‐2017, Chapter11, GeneralTerminalInterface.  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:

           stty tostop

       A background job can be stopped with the command:

           kill -s stop jobID

       The  bg  utility  does not work as expected when it is operating in its own utility execution environment
       because that environment has no suspended jobs. In the following examples:

           ... | xargs bg
           (bg)

       each bg operates in a different environment and does not share its parent shell's understanding of  jobs.
       For this reason, bg is generally implemented as a shell regular built-in.

       Default.

       If job control is disabled, the bg utility shall exit with an error and no job shall  be  placed  in  the
       background.

       Thefollowingsectionsareinformative.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                            BG(1POSIX)

       If  job  control  is  enabled (see the description of set-m), the bg utility shall resume suspended jobs
       from the current environment  (see  Section2.12,  ShellExecutionEnvironment)  by  running  them  as
       background jobs. If the job specified by job_id is already a running background job, the bg utility shall
       have no effect and shall exit successfully.

       Using  bg  to place a job into the background shall cause its process ID to become ``known in the current
       shell execution environment'', as if it had been started as an asynchronous list;  see  Section2.9.3.1,
       Examples.

       The following environment variables shall affect the execution of bg:

       LANG      Provide a default value for the internationalization variables that are unset or null. (See the
                 Base Definitions volume of POSIX.1‐2017, Section8.2, InternationalizationVariables  for  the
                 precedence   of   internationalization  variables  used  to  determine  the  values  of  locale
                 categories.)

       LC_ALL    If set to a non-empty string value, override the values of all the  other  internationalization
                 variables.

       LC_CTYPE  Determine  the  locale  for the interpretation of sequences of bytes of text data as characters
                 (for example, single-byte as opposed to multi-byte characters in arguments).

       LC_MESSAGES
                 Determine the locale that should be used to  affect  the  format  and  contents  of  diagnostic
                 messages written to standard error.

       NLSPATH   Determine the location of message catalogs for the processing of LC_MESSAGES.

       None.

       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.

       None.

       None.

       None.

       bg — run jobs in the background

       The following operand shall be 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 shall be used. The format of job_id is described in the Base Definitions
                 volume of POSIX.1‐2017, Section3.204, JobControlJobID.

       None.

       None.

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

       The  extensions  to the shell specified in this volume of POSIX.1‐2017 have mostly been based on features
       provided by the KornShell. The job control features provided by bg, fg, and jobs are also  based  on  the
       KornShell.  The  standard  developers  examined  the  characteristics  of  the  C shell versions of these
       utilities and found that differences exist. Despite widespread use of the C shell, the KornShell versions
       were selected for this volume of POSIX.1‐2017 to maintain a degree of uniformity with  the  rest  of  the
       KornShell features selected (such as the very popular command line editing features).

       The bg utility is expected to wrap its output if the output exceeds the number of display columns.

Section2.9.3.1, Examples, fg, kill, jobs, wait

       The  Base  Definitions  volume of POSIX.1‐2017, Section3.204, JobControlJobID, Chapter8, EnvironmentVariables, Chapter11, GeneralTerminalInterface

       The standard error shall be used only for diagnostic messages.

       Not used.

       The output of bg shall consist 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.

       bg [job_id...]