287 lines
5.9 KiB
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287 lines
5.9 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 GETHOSTNAME</TITLE>
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</HEAD><BODY>
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<H1>GETHOSTNAME</H1>
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Section: Linux Programmer's Manual (2)<BR>Updated: 2019-10-10<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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gethostname, sethostname - get/set hostname
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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 gethostname(char *</B><I>name</I><B>, size_t </B><I>len</I><B>);</B>
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<BR>
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<B>int sethostname(const char *</B><I>name</I><B>, size_t </B><I>len</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>gethostname</B>():
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<DL COMPACT><DT id="1"><DD>
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Since glibc 2.12:
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_BSD_SOURCE || _XOPEN_SOURCE >= 500
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<BR>
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|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200112L
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</DL>
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<BR>
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<B>sethostname</B>():
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<PRE>
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Since glibc 2.21:
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_DEFAULT_SOURCE
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In glibc 2.19 and 2.20:
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_DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
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Up to and including glibc 2.19:
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_BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
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</PRE>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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These system calls are used to access or to change the system hostname.
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More precisely, they operate on the hostname associated with the calling
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process's UTS namespace.
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<P>
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<B>sethostname</B>()
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sets the hostname to the value given in the character array
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<I>name</I>.
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The
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<I>len</I>
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argument specifies the number of bytes in
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<I>name</I>.
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(Thus,
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<I>name</I>
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does not require a terminating null byte.)
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<P>
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<B>gethostname</B>()
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returns the null-terminated hostname in the character array
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<I>name</I>,
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which has a length of
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<I>len</I>
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bytes.
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If the null-terminated hostname is too large to fit,
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then the name is truncated, and no error is returned (but see NOTES below).
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POSIX.1 says that if such truncation occurs,
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then it is unspecified whether the returned buffer
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includes a terminating null byte.
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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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<DL COMPACT>
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<DT id="2"><B>EFAULT</B>
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<DD>
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<I>name</I>
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is an invalid address.
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<DT id="3"><B>EINVAL</B>
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<DD>
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<I>len</I>
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is negative
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or, for
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<B>sethostname</B>(),
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<I>len</I>
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is larger than the maximum allowed size.
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<DT id="4"><B>ENAMETOOLONG</B>
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<DD>
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(glibc <B>gethostname</B>())
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<I>len</I>
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is smaller than the actual size.
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(Before version 2.1, glibc uses
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<B>EINVAL</B>
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for this case.)
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<DT id="5"><B>EPERM</B>
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<DD>
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For
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<B>sethostname</B>(),
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the caller did not have the
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<B>CAP_SYS_ADMIN</B>
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capability in the user namespace associated with its UTS namespace (see
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<B><A HREF="/cgi-bin/man/man2html?7+namespaces">namespaces</A></B>(7)).
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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 (these interfaces first appeared in 4.2BSD).
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POSIX.1-2001 and POSIX.1-2008 specify
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<B>gethostname</B>()
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but not
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<B>sethostname</B>().
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<A NAME="lbAH"> </A>
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<H2>NOTES</H2>
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SUSv2 guarantees that "Host names are limited to 255 bytes".
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POSIX.1 guarantees that "Host names (not including
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the terminating null byte) are limited to
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<B>HOST_NAME_MAX</B>
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bytes".
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On Linux,
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<B>HOST_NAME_MAX</B>
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is defined with the value 64, which has been the limit since Linux 1.0
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(earlier kernels imposed a limit of 8 bytes).
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<A NAME="lbAI"> </A>
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<H3>C library/kernel differences</H3>
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The GNU C library does not employ the
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<B>gethostname</B>()
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system call; instead, it implements
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<B>gethostname</B>()
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as a library function that calls
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<B><A HREF="/cgi-bin/man/man2html?2+uname">uname</A></B>(2)
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and copies up to
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<I>len</I>
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bytes from the returned
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<I>nodename</I>
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field into
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<I>name</I>.
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Having performed the copy, the function then checks if the length of the
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<I>nodename</I>
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was greater than or equal to
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<I>len</I>,
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and if it is, then the function returns -1 with
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<I>errno</I>
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set to
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<B>ENAMETOOLONG</B>;
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in this case, a terminating null byte is not included in the returned
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<I>name</I>.
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<P>
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Versions of glibc before 2.2
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handle the case where the length of the
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<I>nodename</I>
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was greater than or equal to
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<I>len</I>
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differently: nothing is copied into
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<I>name</I>
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and the function returns -1 with
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<I>errno</I>
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set to
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<B>ENAMETOOLONG</B>.
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<A NAME="lbAJ"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?1+hostname">hostname</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?2+getdomainname">getdomainname</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+setdomainname">setdomainname</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+uname">uname</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?7+uts_namespaces">uts_namespaces</A></B>(7)
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<A NAME="lbAK"> </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="6"><A HREF="#lbAB">NAME</A><DD>
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<DT id="7"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="8"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="9"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="10"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="11"><A HREF="#lbAG">CONFORMING TO</A><DD>
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<DT id="12"><A HREF="#lbAH">NOTES</A><DD>
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<DL>
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<DT id="13"><A HREF="#lbAI">C library/kernel differences</A><DD>
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</DL>
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<DT id="14"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="15"><A HREF="#lbAK">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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