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GETGROUPS
Section: POSIX Programmer's Manual (3P)
Updated: 2003
Index
Return to Main Contents
PROLOG
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
getgroups - get supplementary group IDs
SYNOPSIS
#include <unistd.h>
int getgroups(int gidsetsize, gid_t grouplist[]);
DESCRIPTION
The getgroups() function shall fill in the array grouplist
with the current supplementary group IDs of the calling
process. It is implementation-defined whether getgroups() also
returns the effective group ID in the grouplist
array.
The gidsetsize argument specifies the number of elements in
the array grouplist. The actual number of group IDs
stored in the array shall be returned. The values of array entries
with indices greater than or equal to the value returned are
undefined.
If gidsetsize is 0, getgroups() shall return the number
of group IDs that it would otherwise return without
modifying the array pointed to by grouplist.
If the effective group ID of the process is returned with the supplementary
group IDs, the value returned shall always be
greater than or equal to one and less than or equal to the value of
{NGROUPS_MAX}+1.
RETURN VALUE
Upon successful completion, the number of supplementary group IDs
shall be returned. A return value of -1 indicates failure and
errno shall be set to indicate the error.
ERRORS
The getgroups() function shall fail if:
- EINVAL
-
The gidsetsize argument is non-zero and less than the number
of group IDs that would have been returned.
The following sections are informative.
EXAMPLES
Getting the Supplementary Group IDs of the Calling Process
The following example places the current supplementary group IDs of
the calling process into the group array.
-
#include <sys/types.h>
#include <unistd.h>
...
gid_t *group;
int nogroups;
long ngroups_max;
ngroups_max = sysconf(_SC_NGROUPS_MAX) + 1;
group = (gid_t *)malloc(ngroups_max *sizeof(gid_t));
ngroups = getgroups(ngroups_max, group);
APPLICATION USAGE
None.
RATIONALE
The related function setgroups() is a privileged operation and
therefore is not covered by this volume of
IEEE Std 1003.1-2001.
As implied by the definition of supplementary groups, the effective
group ID may appear in the array returned by
getgroups() or it may be returned only by getegid(). Duplication
may exist,
but the application needs to call getegid() to be sure of getting
all of the
information. Various implementation variations and administrative
sequences cause the set of groups appearing in the result of
getgroups() to vary in order and as to whether the effective
group ID is included, even when the set of groups is the same
(in the mathematical sense of "set"). (The history of a process and
its parents could affect the details of the result.)
Application writers should note that {NGROUPS_MAX} is not necessarily
a constant on all implementations.
FUTURE DIRECTIONS
None.
SEE ALSO
getegid(), setgid(), the Base Definitions volume of
IEEE Std 1003.1-2001, <sys/types.h>, <unistd.h>
COPYRIGHT
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 .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- Getting the Supplementary Group IDs of the Calling Process
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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