core_output_filter: writing data to the network</a></h3>
<p>Apache uses the <code>sendfile</code> syscall on platforms
where it is available in order to speed sending of responses.
Unfortunately, on some systems, Apache will detect the presence of
<code>sendfile</code> at compile-time, even when it does not work
properly. This happens most frequently when using network or
other non-standard file-system.</p>
<p>Symptoms of this problem include the above message in the error
log and zero-length responses to non-zero-sized files. The
problem generally occurs only for static files, since dynamic
content usually does not make use of <code>sendfile</code>.</p>
<p>To fix this problem, simply use the <code class="directive"><a href="../mod/core.html#enablesendfile">EnableSendfile</a></code> directive to disable
<code>sendfile</code> for all or part of your server. Also see
the <code class="directive"><a href="../mod/core.html#enablemmap">EnableMMAP</a></code>, which can
<code>error_log</code>, accompanied by a <code>Forbidden</code>
message to the client usually indicates a problem with your
filesystem permissions, rather than a problem in the Apache HTTP
Server configuration files. Check to make sure that the
<code class="directive"><a href="../mod/mpm_common.html#user">User</a></code> and <code class="directive"><a href="../mod/mpm_common.html#group">Group</a></code> running the child processes
has adequate permission to access the files in question. Also
check that the directory and all parent directories are at least
searchable for that user and group (i.e., <code>chmod
+x</code>).</p>
<p>Recent releases of Fedora Core and other Linux distributions
using SELinux have additional access restrictions beyond those
used by the basic filesystem. Violations of these restrictions
will also result in a <code>Permission denied</code> message. See
the <a href="http://fedora.redhat.com/docs/selinux-faq-fc3/">Fedora
SELinux FAQ</a> and <a href="http://fedora.redhat.com/docs/selinux-apache-fc3/">Apache
SELinux Policy Document</a>.</p>
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