265 lines
6.0 KiB
HTML
265 lines
6.0 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of CHROOT</TITLE>
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</HEAD><BODY>
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<H1>CHROOT</H1>
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Section: Linux Programmer's Manual (2)<BR>Updated: 2019-03-06<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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chroot - change root directory
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>#include <<A HREF="file:///usr/include/unistd.h">unistd.h</A>></B>
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<P>
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<B>int chroot(const char *</B><I>path</I><B>);</B>
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<P>
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Feature Test Macro Requirements for glibc (see
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<B><A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A></B>(7)):
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<P>
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<B>chroot</B>():
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<DL COMPACT><DT id="1"><DD>
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<DL COMPACT>
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<DT id="2">Since glibc 2.2.2:<DD>
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<PRE>
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_XOPEN_SOURCE && ! (_POSIX_C_SOURCE >= 200112L)
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|| /* Since glibc 2.20: */ _DEFAULT_SOURCE
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|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
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<DT id="3"></PRE>
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<DD>
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Before glibc 2.2.2: none
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</DL>
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</DL>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<B>chroot</B>()
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changes the root directory of the calling process to that specified in
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<I>path</I>.
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This directory will be used for pathnames beginning with <I>/</I>.
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The root directory is inherited by all children of the calling process.
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<P>
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Only a privileged process (Linux: one with the
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<B>CAP_SYS_CHROOT</B>
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capability in its user namespace) may call
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<B>chroot</B>().
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<P>
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This call changes an ingredient in the pathname resolution process
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and does nothing else.
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In particular, it is not intended to be used
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for any kind of security purpose, neither to fully sandbox a process nor
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to restrict filesystem system calls.
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In the past,
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<B>chroot</B>()
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has been used by daemons to restrict themselves prior to passing paths
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supplied by untrusted users to system calls such as
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<B><A HREF="/cgi-bin/man/man2html?2+open">open</A></B>(2).
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However, if a folder is moved out of the chroot directory, an attacker
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can exploit that to get out of the chroot directory as well.
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The easiest way to do that is to
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<B><A HREF="/cgi-bin/man/man2html?2+chdir">chdir</A></B>(2)
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to the to-be-moved directory, wait for it to be moved out, then open a
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path like ../../../etc/passwd.
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<P>
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A slightly
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trickier variation also works under some circumstances if
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<B><A HREF="/cgi-bin/man/man2html?2+chdir">chdir</A></B>(2)
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is not permitted.
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If a daemon allows a "chroot directory" to be specified,
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that usually means that if you want to prevent remote users from accessing
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files outside the chroot directory, you must ensure that folders are never
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moved out of it.
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<P>
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This call does not change the current working directory,
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so that after the call '<I>.</I>' can
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be outside the tree rooted at '<I>/</I>'.
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In particular, the superuser can escape from a "chroot jail"
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by doing:
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<P>
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mkdir foo; chroot foo; cd ..
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<P>
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This call does not close open file descriptors, and such file
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descriptors may allow access to files outside the chroot tree.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success, zero is returned.
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On error, -1 is returned, and
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<I>errno</I>
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is set appropriately.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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Depending on the filesystem, other errors can be returned.
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The more general errors are listed below:
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<DL COMPACT>
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<DT id="4"><B>EACCES</B>
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<DD>
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Search permission is denied on a component of the path prefix.
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(See also
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<B><A HREF="/cgi-bin/man/man2html?7+path_resolution">path_resolution</A></B>(7).)
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<DT id="5"><B>EFAULT</B>
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<DD>
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<I>path</I>
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points outside your accessible address space.
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<DT id="6"><B>EIO</B>
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<DD>
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An I/O error occurred.
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<DT id="7"><B>ELOOP</B>
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<DD>
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Too many symbolic links were encountered in resolving
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<I>path</I>.
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<DT id="8"><B>ENAMETOOLONG</B>
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<DD>
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<I>path</I>
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is too long.
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<DT id="9"><B>ENOENT</B>
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<DD>
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The file does not exist.
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<DT id="10"><B>ENOMEM</B>
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<DD>
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Insufficient kernel memory was available.
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<DT id="11"><B>ENOTDIR</B>
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<DD>
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A component of
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<I>path</I>
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is not a directory.
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<DT id="12"><B>EPERM</B>
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<DD>
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The caller has insufficient privilege.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>CONFORMING TO</H2>
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SVr4, 4.4BSD, SUSv2 (marked LEGACY).
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This function is not part of POSIX.1-2001.
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<A NAME="lbAH"> </A>
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<H2>NOTES</H2>
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A child process created via
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<B><A HREF="/cgi-bin/man/man2html?2+fork">fork</A></B>(2)
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inherits its parent's root directory.
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The root directory is left unchanged by
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<B><A HREF="/cgi-bin/man/man2html?2+execve">execve</A></B>(2).
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<P>
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The magic symbolic link,
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<I>/proc/[pid]/root</I>,
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can be used to discover a process's root directory; see
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<B><A HREF="/cgi-bin/man/man2html?5+proc">proc</A></B>(5)
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for details.
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<P>
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FreeBSD has a stronger
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<B>jail</B>()
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system call.
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<A NAME="lbAI"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?1+chroot">chroot</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?2+chdir">chdir</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+pivot_root">pivot_root</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?7+path_resolution">path_resolution</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?8+switch_root">switch_root</A></B>(8)
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<A NAME="lbAJ"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="13"><A HREF="#lbAB">NAME</A><DD>
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<DT id="14"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="15"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="16"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="17"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="18"><A HREF="#lbAG">CONFORMING TO</A><DD>
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<DT id="19"><A HREF="#lbAH">NOTES</A><DD>
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<DT id="20"><A HREF="#lbAI">SEE ALSO</A><DD>
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<DT id="21"><A HREF="#lbAJ">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:32 GMT, March 31, 2021
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</BODY>
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</HTML>
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