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Edit File: mod_tls_shmcache.html

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<title>ProFTPD module mod_tls_shmcache</title>
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<h2>ProFTPD module <code>mod_tls_shmcache</code></h2>
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The <code>mod_tls_shmcache</code> submodule is contained in the
<code>mod_tls_shmcache.c</code> file, and is not compiled by default.
Installation instructions are discussed <a href="#Installation">here</a>.

This submodule provides a SysV shared memory-based implementation of
an external SSL session cache for use by the <code>mod_tls</code> module's
<a href="mod_tls.html#TLSSessionCache"><code>TLSSessionCache</code></a>
directive. The module also implements a SysV shared memory-based
implementation of an external OCSP response cache for the
<a href="mod_tls.html#TLSStaplingCache"><code>TLSStaplingCache</code></a>
directive.

This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit (http://www.openssl.org/).

This product includes cryptographic software written by Eric Young (eay@cryptsoft.com).

<h2>Author</h2>

Please contact TJ Saunders &lt;tj at castaglia.org&gt; with any
questions, concerns, or suggestions regarding this module.

The <code>mod_tls_shmcache</code> module supports the &quot;shm&quot; string
for the type parameter of the
<a href="mod_tls.html#TLSSessionCache"><code>TLSSessionCache</code></a>
configuration directive. The info parameter for
<code>mod_tls_shmcache</code> must be formatted like:
<pre>
 /file=/path/to/cache/file[&amp;size=bytes]
</pre>
The configured path is used for synchronizing access to the shared memory
segment among the various server processes. The default shared memory
segment size allocated is 1.5MB; use the optional size key to
configure a different size, in bytes. Note that the configured size
must be able to hold at least one cached session; if a too-small size
is configured, that size will be ignored and the default size will be used.

The <code>mod_tls_shmcache</code> module also supports the &quot;shm&quot;
string for the type parameter of the
<a href="mod_tls.html#TLSStaplingCache"><code>TLStaplingCache</code></a>
configuration directive. The info parameter for
<code>mod_tls_shmcache</code> must be formatted like:
<pre>
 /file=/path/to/cache/file[&amp;size=bytes]
</pre>
The configured path is used for synchronizing access to the shared memory
segment among the various server processes. The default shared memory
segment size allocated is 1.5MB; use the optional size key to
configure a different size, in bytes. Note that the configured size
must be able to hold at least one cached OCSP response; if a too-small
size is configured, that size will be ignored and the default size will be used.

Examples

Use the default shared memory segment size and timeout:
<pre>
 &lt;IfModule mod_tls.c&gt;
 ...

&lt;IfModule mod_tls_shmcache.c&gt;
 TLSSessionCache shm:/file=/var/ftpd/sess_cache
 TLSStaplingCache shm:/file=/var/ftpd/ocsp_pcache
 &lt;/IfModule&gt;
 &lt;/IfModule&gt;
</pre>

Use a larger shared memory segment size:
<pre>
 &lt;IfModule mod_tls.c&gt;
 ...

&lt;IfModule mod_tls_shmcache.c&gt;
 TLSSessionCache shm:/file=/var/ftpd/sess_cache&amp;size=2097152
 TLSStaplingCache shm:/file=/var/ftpd/ocsp_cache&amp;size=2097152
 &lt;/IfModule&gt;
 &lt;/IfModule&gt;
</pre>

Use a smaller shared memory size, and a shorter timeout:
<pre>
 &lt;IfModule mod_tls.c&gt;
 ...

&lt;IfModule mod_tls_shmcache.c&gt;
      TLSSessionCache shm:/file=/var/ftpd/sess_cache&amp;size=512000 600

# Note that TLSStaplingCache does not use a timeout
 TLSStaplingCache shm:/file=/var/ftpd/ocsp_cache&amp;size=512000
 &lt;/IfModule&gt;
 &lt;/IfModule&gt;
</pre>

<hr>
<h2><a name="Installation">Installation</a></h2>
The <code>mod_tls_shmcache</code> module is distributed with the ProFTPD
source code. Simply follow the normal steps for using third-party modules
in ProFTPD, being sure to include the <code>mod_tls</code> module (on which
<code>mod_tls_shmcache</code> depends):
<pre>
 $ ./configure --with-modules=mod_tls:mod_tls_shmcache
 $ make
 $ make install
</pre>

Alternatively, if your <code>proftpd</code> was compiled with DSO support, you
can use the <code>prxs</code> tool to build <code>mod_tls_shmcache</code> as
a shared module:
<pre>
 $ prxs -c -i -d mod_tls_shmcache.c
</pre>

Note: If using <code>mod_tls_shmcache</code> as a shared module, make
sure that this module is loaded after the <code>mod_tls</code> module,
i.e.:
<pre>
 # Load mod_tls first
 LoadModule mod_tls.c
 
 # Then load any SSL caching modules
 LoadModule mod_tls_shmcache.c
</pre>

<hr>
<h2><a name="Usage">Usage</a></h2>

Logging 
The <code>mod_tls_shmcache</code> module supports <a href="../howto/Tracing.html">trace logging</a>, via the module-specific log channels:
<ul>
 <li>tls.shmcache
</ul>
Thus for trace logging, to aid in debugging, you would use the following in
your <code>proftpd.conf</code>:
<pre>
 TraceLog /path/to/ftpd/trace.log
 Trace tls.shmcache:20
</pre>
This trace logging can generate large files; it is intended for debugging use
only, and should be removed from any production configuration.

<a name="FAQ">
Frequently Asked Questions

<a name="TLSShmcacheEmptyFile">
Question: I configured a <code>TLSSessionCache</code> file, but it is empty. Is <code>mod_tls_shmcache</code> not working properly? 
Answer: Yes, <code>mod_tls_shmcache</code> is working
properly. The actual cache of SSL/TLS session data is stored in shared memory,
not on the filesystem. Storing data in system shared memory requires a unique
key; the <code>mod_tls_shmcache</code> uses the configured file to create
this unique key. The module also uses the configured
<code>TLSSessionCache</code> file for locking, as when handling a
<code>ftpdctl</code> request to clear the cache.

<a name="TLSShmcacheUndefinedSymbol">
Question: I am trying to use
<code>mod_tls_shmcache</code> as a shared module, but my <code>proftpd</code>
server fails to start up, failing with this error:
<pre>
 proftpd: symbol lookup error: /usr/local/libexec/mod_tls_shmcache.so: undefined symbol: tls_sess_cache_register
</pre>
Answer: This happens when your configuration is
loading the <code>mod_tls_shmcache</code> module before the
<code>mod_tls</code> has been loaded. The fix, then, is to make sure
your config looks something like this:
<pre>
 LoadModule mod_tls.c
 LoadModule mod_tls_shmcache.c
</pre>

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