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.1‐2008, 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.1‐2008, 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.1‐2008, 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.1‐2008 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.1‐2008 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.1‐2008, 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, 2013 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers,  Inc
       and  The  Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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 .