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<title>GnuTLS 3.5.4: Debugging and auditing</title>
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<a name="Debugging-and-auditing"></a>
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<p>
Next: <a href="Thread-safety.html#Thread-safety" accesskey="n" rel="next">Thread safety</a>, Previous: <a href="Common-types.html#Common-types" accesskey="p" rel="prev">Common types</a>, Up: <a href="Introduction-to-the-library.html#Introduction-to-the-library" accesskey="u" rel="up">Introduction to the library</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-and-Data-Index.html#Function-and-Data-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Debugging-and-auditing-1"></a>
<h4 class="subsection">6.1.4 Debugging and auditing</h4>
<p>In many cases things may not go as expected and further information,
to assist debugging, from <acronym>GnuTLS</acronym> is desired.
Those are the cases where the <a href="Core-TLS-API.html#gnutls_005fglobal_005fset_005flog_005flevel">gnutls_global_set_log_level</a> and
<a href="Core-TLS-API.html#gnutls_005fglobal_005fset_005flog_005ffunction">gnutls_global_set_log_function</a> are to be used. Those will print
verbose information on the <acronym>GnuTLS</acronym> functions internal flow.
</p>
<dl compact="compact">
<dt><code><var>void</var> <a href="Core-TLS-API.html#gnutls_005fglobal_005fset_005flog_005flevel">gnutls_global_set_log_level</a> (int <var>level</var>)</code></dt>
<dt><code><var>void</var> <a href="Core-TLS-API.html#gnutls_005fglobal_005fset_005flog_005ffunction">gnutls_global_set_log_function</a> (gnutls_log_func <var>log_func</var>)</code></dt>
</dl>
<p>Alternatively the environment variable <code>GNUTLS_DEBUG_LEVEL</code> can be
set to a logging level and GnuTLS will output debugging output to standard
error. Other available environment variables are shown in <a href="#tab_003aenvironment">Table 6.1</a>.
</p>
<div class="float"><a name="tab_003aenvironment"></a>
<table>
<thead><tr><th width="30%">Variable</th><th width="70%">Purpose</th></tr></thead>
<tr><td width="30%"><code>GNUTLS_DEBUG_LEVEL</code></td><td width="70%">When set to a numeric value, it sets the default debugging level for GnuTLS applications.</td></tr>
<tr><td width="30%"><code>SSLKEYLOGFILE</code></td><td width="70%">When set to a filename, GnuTLS will append to it the session keys in the NSS Key Log
format. That format can be read by wireshark and will allow decryption of the session for debugging.</td></tr>
<tr><td width="30%"><code>GNUTLS_CPUID_OVERRIDE</code></td><td width="70%">That environment variable can be used to
explicitly enable/disable the use of certain CPU capabilities. Note that CPU
detection cannot be overridden, i.e., VIA options cannot be enabled on an Intel
CPU. The currently available options are:
<ul>
<li> 0x1: Disable all run-time detected optimizations
</li><li> 0x2: Enable AES-NI
</li><li> 0x4: Enable SSSE3
</li><li> 0x8: Enable PCLMUL
</li><li> 0x10: Enable AVX
</li><li> 0x100000: Enable VIA padlock
</li><li> 0x200000: Enable VIA PHE
</li><li> 0x400000: Enable VIA PHE SHA512
</li></ul></td></tr>
<tr><td width="30%"><code>GNUTLS_FORCE_FIPS_MODE</code></td><td width="70%">In setups where GnuTLS is compiled with support for FIPS140-2 (see –enable-fips140-mode in configure), that option if set to one enforces the FIPS140 mode.</td></tr>
</table>
<div class="float-caption"><p><strong>Table 6.1: </strong>Environment variables used by the library.</p></div></div>
<p>When debugging is not required, important issues, such as detected
attacks on the protocol still need to be logged. This is provided
by the logging function set by
<a href="Core-TLS-API.html#gnutls_005fglobal_005fset_005faudit_005flog_005ffunction">gnutls_global_set_audit_log_function</a>. The provided function
will receive an message and the corresponding
TLS session. The session information might be used to derive IP addresses
or other information about the peer involved.
</p>
<dl>
<dt><a name="index-gnutls_005fglobal_005fset_005faudit_005flog_005ffunction"></a>Function: <em>void</em> <strong>gnutls_global_set_audit_log_function</strong> <em>(gnutls_audit_log_func <var>log_func</var>)</em></dt>
<dd><p><var>log_func</var>: it is the audit log function
</p>
<p>This is the function to set the audit logging function. This
is a function to report important issues, such as possible
attacks in the protocol. This is different from <code>gnutls_global_set_log_function()</code>
because it will report also session-specific events. The session
parameter will be null if there is no corresponding TLS session.
</p>
<p><code>gnutls_audit_log_func</code> is of the form,
void (*gnutls_audit_log_func)( gnutls_session_t, const char*);
</p>
<p><strong>Since:</strong> 3.0
</p></dd></dl>
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Next: <a href="Thread-safety.html#Thread-safety" accesskey="n" rel="next">Thread safety</a>, Previous: <a href="Common-types.html#Common-types" accesskey="p" rel="prev">Common types</a>, Up: <a href="Introduction-to-the-library.html#Introduction-to-the-library" accesskey="u" rel="up">Introduction to the library</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-and-Data-Index.html#Function-and-Data-Index" title="Index" rel="index">Index</a>]</p>
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