PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

SETPGID(3P)               POSIX Programmer's Manual              SETPGID(3P)

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

       setpgid — set process group ID for job control

SYNOPSIS         top

       #include <unistd.h>

       int setpgid(pid_t pid, pid_t pgid);

DESCRIPTION         top

       The setpgid() function shall either join an existing process group or
       create a new process group within the session of the calling process.

       The process group ID of a session leader shall not change.

       Upon successful completion, the process group ID of the process with
       a process ID that matches pid shall be set to pgid.

       As a special case, if pid is 0, the process ID of the calling process
       shall be used. Also, if pgid is 0, the process ID of the indicated
       process shall be used.

RETURN VALUE         top

       Upon successful completion, setpgid() shall return 0; otherwise, −1
       shall be returned and errno shall be set to indicate the error.

ERRORS         top

       The setpgid() function shall fail if:

       EACCES The value of the pid argument matches the process ID of a
              child process of the calling process and the child process has
              successfully executed one of the exec functions.

       EINVAL The value of the pgid argument is less than 0, or is not a
              value supported by the implementation.

       EPERM  The process indicated by the pid argument is a session leader.

       EPERM  The value of the pid argument matches the process ID of a
              child process of the calling process and the child process is
              not in the same session as the calling process.

       EPERM  The value of the pgid argument is valid but does not match the
              process ID of the process indicated by the pid argument and
              there is no process with a process group ID that matches the
              value of the pgid argument in the same session as the calling
              process.

       ESRCH  The value of the pid argument does not match the process ID of
              the calling process or of a child process of the calling
              process.

       The following sections are informative.

EXAMPLES         top

       None.

APPLICATION USAGE         top

       None.

RATIONALE         top

       The setpgid() function shall group processes together for the purpose
       of signaling, placement in foreground or background, and other job
       control actions.

       The setpgid() function is similar to the setpgrp() function of 4.2
       BSD, except that 4.2 BSD allowed the specified new process group to
       assume any value. This presents certain security problems and is more
       flexible than necessary to support job control.

       To provide tighter security, setpgid() only allows the calling
       process to join a process group already in use inside its session or
       create a new process group whose process group ID was equal to its
       process ID.

       When a job control shell spawns a new job, the processes in the job
       must be placed into a new process group via setpgid().  There are two
       timing constraints involved in this action:

        1. The new process must be placed in the new process group before
           the appropriate program is launched via one of the exec
           functions.

        2. The new process must be placed in the new process group before
           the shell can correctly send signals to the new process group.

       To address these constraints, the following actions are performed.
       The new processes call setpgid() to alter their own process groups
       after fork() but before exec.  This satisfies the first constraint.
       Under 4.3 BSD, the second constraint is satisfied by the
       synchronization property of vfork(); that is, the shell is suspended
       until the child has completed the exec, thus ensuring that the child
       has completed the setpgid().  A new version of fork() with this same
       synchronization property was considered, but it was decided instead
       to merely allow the parent shell process to adjust the process group
       of its child processes via setpgid().  Both timing constraints are
       now satisfied by having both the parent shell and the child attempt
       to adjust the process group of the child process; it does not matter
       which succeeds first.

       Since it would be confusing to an application to have its process
       group change after it began executing (that is, after exec), and
       because the child process would already have adjusted its process
       group before this, the [EACCES] error was added to disallow this.

       One non-obvious use of setpgid() is to allow a job control shell to
       return itself to its original process group (the one in effect when
       the job control shell was executed). A job control shell does this
       before returning control back to its parent when it is terminating or
       suspending itself as a way of restoring its job control ``state''
       back to what its parent would expect. (Note that the original process
       group of the job control shell typically matches the process group of
       its parent, but this is not necessarily always the case.)

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       exec(1p), getpgrp(3p), setsid(3p), tcsetpgrp(3p)

       The Base Definitions volume of POSIX.1‐2008, sys_types.h(0p),
       unistd.h(0p)

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                         SETPGID(3P)

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