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SETPGID(3P) POSIX Programmer's Manual SETPGID(3P)
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.
setpgid — set process group ID for job control
#include <unistd.h>
int setpgid(pid_t pid, pid_t pgid);
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.
Upon successful completion, setpgid() shall return 0; otherwise, −1
shall be returned and errno shall be set to indicate the error.
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.
None.
None.
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.)
None.
exec(1p), getpgrp(3p), setsid(3p), tcsetpgrp(3p)
The Base Definitions volume of POSIX.1‐2008, sys_types.h(0p),
unistd.h(0p)
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)
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)