346 lines
7.4 KiB
HTML
346 lines
7.4 KiB
HTML
|
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
|
|
<HTML><HEAD><TITLE>Man page of GETGROUPS</TITLE>
|
|
</HEAD><BODY>
|
|
<H1>GETGROUPS</H1>
|
|
Section: Linux Programmer's Manual (2)<BR>Updated: 2019-03-06<BR><A HREF="#index">Index</A>
|
|
<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
|
|
|
|
<A NAME="lbAB"> </A>
|
|
<H2>NAME</H2>
|
|
|
|
getgroups, setgroups - get/set list of supplementary group IDs
|
|
<A NAME="lbAC"> </A>
|
|
<H2>SYNOPSIS</H2>
|
|
|
|
<B>#include <<A HREF="file:///usr/include/sys/types.h">sys/types.h</A>></B>
|
|
|
|
<BR>
|
|
|
|
<B>#include <<A HREF="file:///usr/include/unistd.h">unistd.h</A>></B>
|
|
|
|
<P>
|
|
|
|
<B>int getgroups(int </B><I>size</I><B>, gid_t </B><I>list</I><B>[]);</B>
|
|
|
|
<P>
|
|
<B>#include <<A HREF="file:///usr/include/grp.h">grp.h</A>></B>
|
|
|
|
<P>
|
|
|
|
<B>int setgroups(size_t </B><I>size</I><B>, const gid_t *</B><I>list</I><B>);</B>
|
|
|
|
<P>
|
|
|
|
|
|
Feature Test Macro Requirements for glibc (see
|
|
<B><A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A></B>(7)):
|
|
|
|
|
|
<P>
|
|
|
|
<B>setgroups</B>():
|
|
|
|
<BR> Since glibc 2.19:
|
|
<BR> _DEFAULT_SOURCE
|
|
<BR> Glibc 2.19 and earlier:
|
|
<BR> _BSD_SOURCE
|
|
<A NAME="lbAD"> </A>
|
|
<H2>DESCRIPTION</H2>
|
|
|
|
<P>
|
|
|
|
<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>
|
|
|
|
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><A HREF="/cgi-bin/man/man2html?2+getegid">getegid</A></B>(2)
|
|
|
|
and add or remove the resulting value.)
|
|
<P>
|
|
|
|
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>
|
|
|
|
<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>
|
|
|
|
|
|
|
|
setgroups(0, NULL);
|
|
|
|
|
|
<A NAME="lbAE"> </A>
|
|
<H2>RETURN VALUE</H2>
|
|
|
|
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>
|
|
|
|
On success,
|
|
<B>setgroups</B>()
|
|
|
|
returns 0.
|
|
On error, -1 is returned, and
|
|
<I>errno</I>
|
|
|
|
is set appropriately.
|
|
<A NAME="lbAF"> </A>
|
|
<H2>ERRORS</H2>
|
|
|
|
<DL COMPACT>
|
|
<DT id="1"><B>EFAULT</B>
|
|
|
|
<DD>
|
|
<I>list</I>
|
|
|
|
has an invalid address.
|
|
</DL>
|
|
<P>
|
|
|
|
<B>getgroups</B>()
|
|
|
|
can additionally fail with the following error:
|
|
<DL COMPACT>
|
|
<DT id="2"><B>EINVAL</B>
|
|
|
|
<DD>
|
|
<I>size</I>
|
|
|
|
is less than the number of supplementary group IDs, but is not zero.
|
|
</DL>
|
|
<P>
|
|
|
|
<B>setgroups</B>()
|
|
|
|
can additionally fail with the following errors:
|
|
<DL COMPACT>
|
|
<DT id="3"><B>EINVAL</B>
|
|
|
|
<DD>
|
|
<I>size</I>
|
|
|
|
is greater than
|
|
<B>NGROUPS_MAX</B>
|
|
|
|
(32 before Linux 2.6.4; 65536 since Linux 2.6.4).
|
|
<DT id="4"><B>ENOMEM</B>
|
|
|
|
<DD>
|
|
Out of memory.
|
|
<DT id="5"><B>EPERM</B>
|
|
|
|
<DD>
|
|
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).
|
|
<DT id="6"><B>EPERM</B> (since Linux 3.19)
|
|
|
|
<DD>
|
|
The use of
|
|
<B>setgroups</B>()
|
|
|
|
is denied in this user namespace.
|
|
See the description of
|
|
<I>/proc/[pid]/setgroups</I>
|
|
|
|
in
|
|
<B><A HREF="/cgi-bin/man/man2html?7+user_namespaces">user_namespaces</A></B>(7).
|
|
|
|
</DL>
|
|
<A NAME="lbAG"> </A>
|
|
<H2>CONFORMING TO</H2>
|
|
|
|
<B>getgroups</B>():
|
|
|
|
SVr4, 4.3BSD, POSIX.1-2001, POSIX.1-2008.
|
|
<P>
|
|
|
|
<B>setgroups</B>():
|
|
|
|
SVr4, 4.3BSD.
|
|
Since
|
|
<B>setgroups</B>()
|
|
|
|
requires privilege, it is not covered by POSIX.1.
|
|
<A NAME="lbAH"> </A>
|
|
<H2>NOTES</H2>
|
|
|
|
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><<A HREF="file:///usr/include/limits.h">limits.h</A>></I>.
|
|
|
|
The set of supplementary group IDs
|
|
is inherited from the parent process, and preserved across an
|
|
<B><A HREF="/cgi-bin/man/man2html?2+execve">execve</A></B>(2).
|
|
|
|
<P>
|
|
|
|
The maximum number of supplementary group IDs can be found at run time using
|
|
<B><A HREF="/cgi-bin/man/man2html?3+sysconf">sysconf</A></B>(3):
|
|
|
|
<P>
|
|
|
|
|
|
|
|
long ngroups_max;
|
|
ngroups_max = sysconf(_SC_NGROUPS_MAX);
|
|
|
|
|
|
<P>
|
|
|
|
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>
|
|
|
|
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.
|
|
|
|
<A NAME="lbAI"> </A>
|
|
<H3>C library/kernel differences</H3>
|
|
|
|
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><A HREF="/cgi-bin/man/man2html?7+nptl">nptl</A></B>(7).
|
|
|
|
<A NAME="lbAJ"> </A>
|
|
<H2>SEE ALSO</H2>
|
|
|
|
<B><A HREF="/cgi-bin/man/man2html?2+getgid">getgid</A></B>(2),
|
|
|
|
<B><A HREF="/cgi-bin/man/man2html?2+setgid">setgid</A></B>(2),
|
|
|
|
<B><A HREF="/cgi-bin/man/man2html?3+getgrouplist">getgrouplist</A></B>(3),
|
|
|
|
<B><A HREF="/cgi-bin/man/man2html?3+group_member">group_member</A></B>(3),
|
|
|
|
<B><A HREF="/cgi-bin/man/man2html?3+initgroups">initgroups</A></B>(3),
|
|
|
|
<B><A HREF="/cgi-bin/man/man2html?7+capabilities">capabilities</A></B>(7),
|
|
|
|
<B><A HREF="/cgi-bin/man/man2html?7+credentials">credentials</A></B>(7)
|
|
|
|
<A NAME="lbAK"> </A>
|
|
<H2>COLOPHON</H2>
|
|
|
|
This page is part of release 5.05 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
|
|
<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
|
|
<P>
|
|
|
|
<HR>
|
|
<A NAME="index"> </A><H2>Index</H2>
|
|
<DL>
|
|
<DT id="7"><A HREF="#lbAB">NAME</A><DD>
|
|
<DT id="8"><A HREF="#lbAC">SYNOPSIS</A><DD>
|
|
<DT id="9"><A HREF="#lbAD">DESCRIPTION</A><DD>
|
|
<DT id="10"><A HREF="#lbAE">RETURN VALUE</A><DD>
|
|
<DT id="11"><A HREF="#lbAF">ERRORS</A><DD>
|
|
<DT id="12"><A HREF="#lbAG">CONFORMING TO</A><DD>
|
|
<DT id="13"><A HREF="#lbAH">NOTES</A><DD>
|
|
<DL>
|
|
<DT id="14"><A HREF="#lbAI">C library/kernel differences</A><DD>
|
|
</DL>
|
|
<DT id="15"><A HREF="#lbAJ">SEE ALSO</A><DD>
|
|
<DT id="16"><A HREF="#lbAK">COLOPHON</A><DD>
|
|
</DL>
|
|
<HR>
|
|
This document was created by
|
|
<A HREF="/cgi-bin/man/man2html">man2html</A>,
|
|
using the manual pages.<BR>
|
|
Time: 00:05:32 GMT, March 31, 2021
|
|
</BODY>
|
|
</HTML>
|