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gethostname.html
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<!-- Creator : groff version 1.22.4 -->
<!-- CreationDate: Wed Jan 29 11:27:03 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>GETHOSTNAME</title>
</head>
<body>
<h1 align="center">GETHOSTNAME</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">gethostname,
sethostname - get/set hostname</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>#include
<unistd.h></b></p>
<p style="margin-left:11%; margin-top: 1em"><b>int
gethostname(char *</b><i>name</i><b>, size_t</b>
<i>len</i><b>); <br>
int sethostname(const char *</b><i>name</i><b>, size_t</b>
<i>len</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>gethostname</b>():</p>
<p style="margin-left:17%;">Since glibc 2.12: _BSD_SOURCE
|| _XOPEN_SOURCE >= 500 <br>
|| /* Since glibc 2.12: */
_POSIX_C_SOURCE >= 200112L</p>
<p style="margin-left:11%;"><b>sethostname</b>(): <br>
Since glibc 2.21: <br>
_DEFAULT_SOURCE <br>
In glibc 2.19 and 2.20: <br>
_DEFAULT_SOURCE || (_XOPEN_SOURCE &&
_XOPEN_SOURCE < 500) <br>
Up to and including glibc 2.19: <br>
_BSD_SOURCE || (_XOPEN_SOURCE &&
_XOPEN_SOURCE < 500)</p>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">These system
calls are used to access or to change the hostname of the
current processor.</p>
<p style="margin-left:11%; margin-top: 1em"><b>sethostname</b>()
sets the hostname to the value given in the character array
<i>name</i>. The <i>len</i> argument specifies the number of
bytes in <i>name</i>. (Thus, <i>name</i> does not require a
terminating null byte.)</p>
<p style="margin-left:11%; margin-top: 1em"><b>gethostname</b>()
returns the null-terminated hostname in the character array
<i>name</i>, which has a length of <i>len</i> bytes. If the
null-terminated hostname is too large to fit, then the name
is truncated, and no error is returned (but see NOTES
below). POSIX.1 says that if such truncation occurs, then it
is unspecified whether the returned buffer includes a
terminating null byte.</p>
<h2>RETURN VALUE
<a name="RETURN VALUE"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">On success,
zero is returned. 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="78%">
<p style="margin-top: 1em"><i>name</i> is an invalid
address.</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p><b>EINVAL</b></p></td>
<td width="2%"></td>
<td width="78%">
<p><i>len</i> is negative or, for <b>sethostname</b>(),
<i>len</i> is larger than the maximum allowed size.</p></td></tr>
</table>
<p style="margin-left:11%;"><b>ENAMETOOLONG</b></p>
<p style="margin-left:22%;">(glibc <b>gethostname</b>())
<i>len</i> is smaller than the actual size. (Before version
2.1, glibc uses <b>EINVAL</b> for this case.)</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="7%">
<p><b>EPERM</b></p></td>
<td width="4%"></td>
<td width="78%">
<p>For <b>sethostname</b>(), the caller did not have the
<b>CAP_SYS_ADMIN</b> capability in the user namespace
associated with its UTS namespace (see
<b>namespaces</b>(7)).</p> </td></tr>
</table>
<h2>CONFORMING TO
<a name="CONFORMING TO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">SVr4, 4.4BSD
(these interfaces first appeared in 4.2BSD). POSIX.1-2001
and POSIX.1-2008 specify <b>gethostname</b>() but not
<b>sethostname</b>().</p>
<h2>NOTES
<a name="NOTES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">SUSv2
guarantees that "Host names are limited to 255
bytes". POSIX.1 guarantees that "Host names (not
including the terminating null byte) are limited to
<b>HOST_NAME_MAX</b> bytes". On Linux,
<b>HOST_NAME_MAX</b> is defined with the value 64, which has
been the limit since Linux 1.0 (earlier kernels imposed a
limit of 8 bytes).</p>
<p style="margin-left:11%; margin-top: 1em"><b>C
library/kernel differences</b> <br>
The GNU C library does not employ the <b>gethostname</b>()
system call; instead, it implements <b>gethostname</b>() as
a library function that calls <b>uname</b>(2) and copies up
to <i>len</i> bytes from the returned <i>nodename</i> field
into <i>name</i>. Having performed the copy, the function
then checks if the length of the <i>nodename</i> was greater
than or equal to <i>len</i>, and if it is, then the function
returns -1 with <i>errno</i> set to <b>ENAMETOOLONG</b>; in
this case, a terminating null byte is not included in the
returned <i>name</i>.</p>
<p style="margin-left:11%; margin-top: 1em">Versions of
glibc before 2.2 handle the case where the length of the
<i>nodename</i> was greater than or equal to <i>len</i>
differently: nothing is copied into <i>name</i> and the
function returns -1 with <i>errno</i> set to
<b>ENAMETOOLONG</b>.</p>
<h2>SEE ALSO
<a name="SEE ALSO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>hostname</b>(1),
<b>getdomainname</b>(2), <b>setdomainname</b>(2),
<b>uname</b>(2)</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>