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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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GETGROUPS(3P) POSIX Programmer's Manual GETGROUPS(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.
getgroups — get supplementary group IDs
#include <unistd.h>
int getgroups(int gidsetsize, gid_t grouplist[]);
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.
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.
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.
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);
None.
The related function setgroups() is a privileged operation and
therefore is not covered by this volume of POSIX.1‐2017.
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 developers should note that {NGROUPS_MAX} is not
necessarily a constant on all implementations.
None.
getegid(3p), setgid(3p)
The Base Definitions volume of POSIX.1‐2017, sys_types.h(0p),
unistd.h(0p)
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 GETGROUPS(3P)
Pages that refer to this page: unistd.h(0p), id(1p), open(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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