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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 ManualSETPGID(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_tpid, pid_tpgid);

DESCRIPTION top

       Thesetpgid() 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 matchespid shall be set topgid.       As a special case, ifpid is 0, the process ID of the calling       process shall be used. Also, ifpgid 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 anderrno shall be set to indicate the error.

ERRORS top

       Thesetpgid() function shall fail if:EACCESThe value of thepid argument matches the process ID of a              child process of the calling process and the child process              has successfully executed one of theexec functions.EINVALThe value of thepgid argument is less than 0, or is not a              value supported by the implementation.EPERMThe process indicated by thepid argument is a session              leader.EPERMThe value of thepid 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.EPERMThe value of thepgid argument is valid but does not match              the process ID of the process indicated by thepid argument              and there is no process with a process group ID that              matches the value of thepgid argument in the same session              as the calling process.ESRCHThe value of thepid 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

       Thesetpgid() function shall group processes together for the       purpose of signaling, placement in foreground or background, and       other job control actions.       Thesetpgid() function is similar to thesetpgrp() 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 viasetpgid().  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 theexec           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 callsetpgid() to alter their own process groups       afterfork() but beforeexec.  This satisfies the first       constraint. Under 4.3 BSD, the second constraint is satisfied by       the synchronization property ofvfork(); that is, the shell is       suspended until the child has completed theexec, thus ensuring       that the child has completed thesetpgid().  A new version offork() 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 viasetpgid().       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, afterexec), 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 ofsetpgid() 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.

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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group                2017SETPGID(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)