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PROLOG

       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.

NAME

       bg — run jobs in the background

SYNOPSIS

       bg [job_id...]

DESCRIPTION

       If  job  control  is  enabled (see the description of set -m), the bg utility shall resume
       suspended  jobs  from  the  current  environment  (see  Section  2.12,   Shell   Execution
       Environment) 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 Section 2.9.3.1, Examples.

OPTIONS

       None.

OPERANDS

       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,  Section  3.204,  Job
                 Control Job ID.

STDIN

       Not used.

INPUT FILES

       None.

ENVIRONMENT VARIABLES

       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,   Section   8.2,
                 Internationalization   Variables  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.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       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.

STDERR

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.

CONSEQUENCES OF ERRORS

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

       The following sections are informative.

APPLICATION USAGE

       A  job  is generally suspended by typing the SUSP character (<control>‐Z on most systems);
       see the Base Definitions volume of POSIX.1‐2017, Chapter 11, General  Terminal  Interface.
       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 job ID

       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.

EXAMPLES

       None.

RATIONALE

       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.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Section 2.9.3.1, Examples, fg, kill, jobs, wait

       The Base Definitions volume of POSIX.1‐2017, Section 3.204, Job Control Job ID, Chapter 8,
       Environment Variables, Chapter 11, General Terminal Interface

COPYRIGHT

       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 .