GETGROUPS(P) POSIX Programmer's Manual GETGROUPS(P)NAMEgetgroups - 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 implemen‐
tation-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 supple‐
mentary 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 there‐
fore 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 ALSOgetegid() , 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 .
IEEE/The Open Group 2003 GETGROUPS(P)
