Originální popis anglicky:
setpgid - set process group ID for job control
Návod, kniha: POSIX Programmer's Manual
#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() ,
getpgrp() ,
setsid() ,
tcsetpgrp() , the
Base Definitions volume of IEEE Std 1003.1-2001,
<sys/types.h>,
<unistd.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 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
.
