setpgid(3p) — Linux manual page

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.1‐2017, sys_types.h(0p),
       unistd.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, 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                       SETPGID(3P)

Pages that refer to this page: unistd.h(0p)_Exit(3p)getpgid(3p)getpgrp(3p)getpid(3p)getppid(3p)getsid(3p)posix_spawn(3p)setpgrp(3p)setsid(3p)tcgetpgrp(3p)