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.\" Copyright (c) 1983, 1991, 1993, 1994
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.\" @(#)setgroups.2 8.2 (Berkeley) 4/16/94
.\" $FreeBSD$
.\"
.Dd January 19, 2018
.Dt SETGROUPS 2
.Os
.Sh NAME
.Nm setgroups
.Nd set group access list
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/param.h
.In unistd.h
.Ft int
.Fn setgroups "int ngroups" "const gid_t *gidset"
.Sh DESCRIPTION
The
.Fn setgroups
system call
sets the group access list of the current user process
according to the array
.Fa gidset .
The
.Fa ngroups
argument
indicates the number of entries in the array and must be no
more than
.Dv {NGROUPS_MAX}+1 .
.Pp
Only the super-user may set a new group list.
.Pp
The first entry of the group array
.Pq Va gidset[0]
is used as the effective group-ID for the process.
This entry is over-written when a setgid program is run.
To avoid losing access to the privileges of the
.Va gidset[0]
entry, it should be duplicated later in the group array.
By convention,
this happens because the group value indicated
in the password file also appears in
.Pa /etc/group .
The group value in the password file is placed in
.Va gidset[0]
and that value then gets added a second time when the
.Pa /etc/group
file is scanned to create the group set.
.Sh RETURN VALUES
.Rv -std setgroups
.Sh ERRORS
The
.Fn setgroups
system call will fail if:
.Bl -tag -width Er
.It Bq Er EPERM
The caller is not the super-user.
.It Bq Er EINVAL
The number specified in the
.Fa ngroups
argument is larger than the
.Dv {NGROUPS_MAX}+1
limit.
.It Bq Er EFAULT
The address specified for
.Fa gidset
is outside the process
address space.
.El
.Sh SEE ALSO
.Xr getgroups 2 ,
.Xr initgroups 3
.Sh HISTORY
The
.Fn setgroups
system call appeared in
.Bx 4.2 .
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