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.\"     @(#)getgroups.2	8.2 (Berkeley) 4/16/94
.\"
.Dd October 28, 2011
.Dt GETGROUPS 2
.Os BSD 4.2
.Sh NAME
.Nm getgroups
.Nd get group access list
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fo getgroups
.Fa "int gidsetsize"
.Fa "gid_t grouplist[]"
.Fc
.Sh DESCRIPTION
.Fn getgroups
gets the current group access list of the current user process
and stores it in the array 
.Fa grouplist[] .
The parameter
.Fa gidsetsize
indicates the number of entries that may be placed in 
.Fa grouplist[] .
.Fn getgroups
returns the actual number of groups returned in
.Fa grouplist[] .
However, no more than
.Dv {NGROUPS_MAX}
will be returned. If
.Fa gidsetsize
is 0, 
.Fn getgroups
returns the number of groups without modifying the
.Fa grouplist[]
array.
.Pp
Calling
.Xr initgroups 3
to opt-in for supplementary groups will cause
.Fn getgroups
to return a single entry, the GID that was passed to 
.Xr initgroups 3 .
.Pp
To provide compatibility with applications that use
.Fn getgroups
in environments where users may be in more than
.Dv {NGROUPS_MAX}
groups, a variant of
.Fn getgroups ,
obtained when compiling with either the macros
.Dv _DARWIN_UNLIMITED_GETGROUPS
or
.Dv _DARWIN_C_SOURCE
defined, can be used that is not limited to
.Dv {NGROUPS_MAX}
groups.
However, this variant only returns the user's default group access list and
not the group list modified by a call to
.Xr setgroups 2
(either in the current process or an ancestor process).
Use of
.Xr setgroups 2
is highly discouraged, and there is no foolproof way to determine if it has
been previously called.
.Sh RETURN VALUES
A successful call returns the number of groups in the group set.
Otherwise, a value of -1 is returned and the global integer variable
.Va errno
is set to indicate the error.
.Sh ERRORS
The possible errors for
.Fn getgroups
are:
.Bl -tag -width Er
.\" ==========
.It Bq Er EFAULT
The argument
.Fa grouplist
specifies an invalid address.
.\" ==========
.It Bq Er EINVAL
The argument
.Fa gidsetsize ,
although non-zero,
is smaller than the number of groups in the group set.
.El
.Sh LEGACY SYNOPSIS
.Fd #include <sys/param.h>
.Fd #include <sys/types.h>
.Fd #include <unistd.h>
.Pp
The include files
.In sys/param.h
and
.In sys/types.h
are necessary.
.Sh SEE ALSO
.Xr setgroups 2 ,
.Xr initgroups 3 ,
.Xr compat 5
.Sh HISTORY
The
.Fn getgroups
function call appeared in
.Bx 4.2 .