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.\"     @(#)getgroups.2	8.2 (Berkeley) 4/16/94
.\" $FreeBSD: head/lib/libc/sys/getgroups.2 217704 2011-01-21 22:15:17Z jilles $
.\"
.Dd January 21, 2011
.Dt GETGROUPS 2
.Os
.Sh NAME
.Nm getgroups
.Nd get group access list
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn getgroups "int gidsetlen" "gid_t *gidset"
.Sh DESCRIPTION
The
.Fn getgroups
system call
gets the current group access list of the user process
and stores it in the array
.Fa gidset .
The
.Fa gidsetlen
argument
indicates the number of entries that may be placed in
.Fa gidset .
The
.Fn getgroups
system call
returns the actual number of groups returned in
.Fa gidset .
At least one and as many as {NGROUPS_MAX}+1 values may be returned.
If
.Fa gidsetlen
is zero,
.Fn getgroups
returns the number of supplementary group IDs associated with
the calling process without modifying the array pointed to by
.Fa gidset .
.Pp
The value of
.Dv {NGROUPS_MAX}
should be obtained using
.Xr sysconf 3
to avoid hard-coding it into the executable.
.Sh RETURN VALUES
A successful call returns the number of groups in the group set.
A value of -1 indicates that an error occurred, and the error
code is stored in the global variable
.Va errno .
.Sh ERRORS
The possible errors for
.Fn getgroups
are:
.Bl -tag -width Er
.It Bq Er EINVAL
The argument
.Fa gidsetlen
is smaller than the number of groups in the group set.
.It Bq Er EFAULT
The argument
.Fa gidset
specifies
an invalid address.
.El
.Sh SEE ALSO
.Xr setgroups 2 ,
.Xr initgroups 3 ,
.Xr sysconf 3
.Sh STANDARDS
The
.Fn getgroups
system call conforms to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn getgroups
system call appeared in
.Bx 4.2 .