PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

BG(1P)                    POSIX Programmer's Manual                   BG(1P)

PROLOG         top

       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         top

       bg — run jobs in the background

SYNOPSIS         top

       bg [job_id...]

DESCRIPTION         top

       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         top

       None.

OPERANDS         top

       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         top

       Not used.

INPUT FILES         top

       None.

ENVIRONMENT VARIABLES         top

       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         top

       Default.

STDOUT         top

       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         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.

CONSEQUENCES OF ERRORS         top

       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         top

       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         top

       None.

RATIONALE         top

       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         top

       None.

SEE ALSO         top

       Section 2.9.3.1, Examples, fg(1p), kill(1p), jobs(1p), wait(1p)

       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         top

       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 .

IEEE/The Open Group                 2013                              BG(1P)