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getgroups.html
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<!-- Creator : groff version 1.22.4 -->
<!-- CreationDate: Wed Jan 29 11:26:58 2020 -->
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta name="generator" content="groff -Thtml, see www.gnu.org">
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<meta name="Content-Style" content="text/css">
<style type="text/css">
p { margin-top: 0; margin-bottom: 0; vertical-align: top }
pre { margin-top: 0; margin-bottom: 0; vertical-align: top }
table { margin-top: 0; margin-bottom: 0; vertical-align: top }
h1 { text-align: center }
</style>
<title>GETGROUPS</title>
</head>
<body>
<h1 align="center">GETGROUPS</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#RETURN VALUE">RETURN VALUE</a><br>
<a href="#ERRORS">ERRORS</a><br>
<a href="#CONFORMING TO">CONFORMING TO</a><br>
<a href="#NOTES">NOTES</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#COLOPHON">COLOPHON</a><br>
<hr>
<h2>NAME
<a name="NAME"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">getgroups,
setgroups - get/set list of supplementary group IDs</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>#include
<sys/types.h> <br>
#include <unistd.h></b></p>
<p style="margin-left:11%; margin-top: 1em"><b>int
getgroups(int</b> <i>size</i><b>, gid_t</b>
<i>list</i><b>[]);</b></p>
<p style="margin-left:11%; margin-top: 1em"><b>#include
<grp.h></b></p>
<p style="margin-left:11%; margin-top: 1em"><b>int
setgroups(size_t</b> <i>size</i><b>, const gid_t
*</b><i>list</i><b>);</b></p>
<p style="margin-left:5%; margin-top: 1em">Feature Test
Macro Requirements for glibc (see
<b>feature_test_macros</b>(7)):</p>
<p style="margin-left:11%; margin-top: 1em"><b>setgroups</b>():
<br>
Since glibc 2.19: <br>
_DEFAULT_SOURCE <br>
Glibc 2.19 and earlier: <br>
_BSD_SOURCE</p>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>getgroups</b>()
returns the supplementary group IDs of the calling process
in <i>list</i>. The argument <i>size</i> should be set to
the maximum number of items that can be stored in the buffer
pointed to by <i>list</i>. If the calling process is a
member of more than <i>size</i> supplementary groups, then
an error results.</p>
<p style="margin-left:11%; margin-top: 1em">It is
unspecified whether the effective group ID of the calling
process is included in the returned list. (Thus, an
application should also call <b>getegid</b>(2) and add or
remove the resulting value.)</p>
<p style="margin-left:11%; margin-top: 1em">If <i>size</i>
is zero, <i>list</i> is not modified, but the total number
of supplementary group IDs for the process is returned. This
allows the caller to determine the size of a dynamically
allocated <i>list</i> to be used in a further call to
<b>getgroups</b>().</p>
<p style="margin-left:11%; margin-top: 1em"><b>setgroups</b>()
sets the supplementary group IDs for the calling process.
Appropriate privileges are required (see the description of
the <b>EPERM</b> error, below). The <i>size</i> argument
specifies the number of supplementary group IDs in the
buffer pointed to by <i>list</i>. A process can drop all of
its supplementary groups with the call:</p>
<p style="margin-left:17%; margin-top: 1em">setgroups(0,
NULL);</p>
<h2>RETURN VALUE
<a name="RETURN VALUE"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">On success,
<b>getgroups</b>() returns the number of supplementary group
IDs. On error, -1 is returned, and <i>errno</i> is set
appropriately.</p>
<p style="margin-left:11%; margin-top: 1em">On success,
<b>setgroups</b>() returns 0. On error, -1 is returned, and
<i>errno</i> is set appropriately.</p>
<h2>ERRORS
<a name="ERRORS"></a>
</h2>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em"><b>EFAULT</b></p></td>
<td width="2%"></td>
<td width="43%">
<p style="margin-top: 1em"><i>list</i> has an invalid
address.</p> </td>
<td width="35%">
</td></tr>
</table>
<p style="margin-left:11%; margin-top: 1em"><b>getgroups</b>()
can additionally fail with the following error:</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em"><b>EINVAL</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em"><i>size</i> is less than the
number of supplementary group IDs, but is not zero.</p></td></tr>
</table>
<p style="margin-left:11%; margin-top: 1em"><b>setgroups</b>()
can additionally fail with the following errors:</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em"><b>EINVAL</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em"><i>size</i> is greater than
<b>NGROUPS_MAX</b> (32 before Linux 2.6.4; 65536 since Linux
2.6.4).</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p><b>ENOMEM</b></p></td>
<td width="2%"></td>
<td width="78%">
<p>Out of memory.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p><b>EPERM</b></p></td>
<td width="2%"></td>
<td width="78%">
<p>The calling process has insufficient privilege (the
caller does not have the <b>CAP_SETGID</b> capability in the
user namespace in which it resides).</p></td></tr>
</table>
<p style="margin-left:11%;"><b>EPERM</b> (since Linux
3.19)</p>
<p style="margin-left:22%;">The use of <b>setgroups</b>()
is denied in this user namespace. See the description of
<i>/proc/[pid]/setgroups</i> in
<b>user_namespaces</b>(7).</p>
<h2>CONFORMING TO
<a name="CONFORMING TO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>getgroups</b>():
SVr4, 4.3BSD, POSIX.1-2001, POSIX.1-2008.</p>
<p style="margin-left:11%; margin-top: 1em"><b>setgroups</b>():
SVr4, 4.3BSD. Since <b>setgroups</b>() requires privilege,
it is not covered by POSIX.1.</p>
<h2>NOTES
<a name="NOTES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">A process can
have up to <b>NGROUPS_MAX</b> supplementary group IDs in
addition to the effective group ID. The constant
<b>NGROUPS_MAX</b> is defined in <i><limits.h></i>.
The set of supplementary group IDs is inherited from the
parent process, and preserved across an
<b>execve</b>(2).</p>
<p style="margin-left:11%; margin-top: 1em">The maximum
number of supplementary group IDs can be found at run time
using <b>sysconf</b>(3):</p>
<p style="margin-left:17%; margin-top: 1em">long
ngroups_max; <br>
ngroups_max = sysconf(_SC_NGROUPS_MAX);</p>
<p style="margin-left:11%; margin-top: 1em">The maximum
return value of <b>getgroups</b>() cannot be larger than one
more than this value. Since Linux 2.6.4, the maximum number
of supplementary group IDs is also exposed via the
Linux-specific read-only file,
<i>/proc/sys/kernel/ngroups_max</i>.</p>
<p style="margin-left:11%; margin-top: 1em">The original
Linux <b>getgroups</b>() system call supported only 16-bit
group IDs. Subsequently, Linux 2.4 added
<b>getgroups32</b>(), supporting 32-bit IDs. The glibc
<b>getgroups</b>() wrapper function transparently deals with
the variation across kernel versions.</p>
<p style="margin-left:11%; margin-top: 1em"><b>C
library/kernel differences</b> <br>
At the kernel level, user IDs and group IDs are a per-thread
attribute. However, POSIX requires that all threads in a
process share the same credentials. The NPTL threading
implementation handles the POSIX requirements by providing
wrapper functions for the various system calls that change
process UIDs and GIDs. These wrapper functions (including
the one for <b>setgroups</b>()) employ a signal-based
technique to ensure that when one thread changes
credentials, all of the other threads in the process also
change their credentials. For details, see
<b>nptl</b>(7).</p>
<h2>SEE ALSO
<a name="SEE ALSO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>getgid</b>(2),
<b>setgid</b>(2), <b>getgrouplist</b>(3),
<b>group_member</b>(3), <b>initgroups</b>(3),
<b>capabilities</b>(7), <b>credentials</b>(7)</p>
<h2>COLOPHON
<a name="COLOPHON"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">This page is
part of release 5.02 of the Linux <i>man-pages</i> project.
A description of the project, information about reporting
bugs, and the latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.</p>
<hr>
</body>
</html>