Caching With Apache's mod_cache On Debian Etch

Version 1.0
Author: Falko Timme

This article explains how you can cache your web site contents with Apache's mod_cache on Debian Etch. If you have a high-traffic dynamic web site that generates lots of database queries on each request, you can decrease the server load dramatically by caching your content for a few minutes or more (that depends on how often you update your content).

I do not issue any guarantee that this will work for you!


1 Preliminary Note

I'm assuming that you have a working Apache2 setup (Apache 2.2.x - prior to that version, mod_cache is considered experimental) from the Debian repositories - the Apache version in the Debian Etch repositories is 2.2.3 so you should be good to go.

I'm using the document root /var/www here for my test vhost - you must adjust this if your document root differs.


2 Enabling mod_cache

mod_cache has two submodules that manage the cache storage, mod_disk_cache (for storing contents on the hard drive) and mod_mem_cache (for storing contents in memory which is faster than disk caching). Decide which one you want to use and continue either with chapter 2.1 (mod_disk_cache) or 2.2 (mod_mem_cache).


2.1 mod_disk_cache

The mod_disk_cache configuration is stored in /etc/apache2/mods-available/disk_cache.conf, so let's edit that one:

vi /etc/apache2/mods-available/disk_cache.conf

Make sure you uncomment the CacheEnable disk / line, so that the minimal configuration looks as follows:

# a2enmod-note: needs-configuration

<IfModule mod_disk_cache.c>
        CacheRoot /var/cache/apache2/mod_disk_cache

# If you enable disk caching, you need to use htcacheclean from the
# apache2-utils package to ensure that the cache does not grow indefinitely.
# See the htcacheclean man page for details.

# There is currently no mechanism in the Debian package to start htcacheclean
# automatically, but it is planned to add such a mechanism in the future.

        CacheEnable disk /

        CacheDirLevels 5
        CacheDirLength 3

You can find explanations for these configuration options and further configuration options on

Now we can enable mod_cache and mod_disk_cache:

a2enmod cache
a2enmod disk_cache

/etc/init.d/apache2 force-reload

To make sure that our cache directory /var/cache/apache2/mod_disk_cache doesn't fill up over time, we have to clean it with the htcacheclean command. That command is part of the apache2-utils package which we install as follows:

apt-get install apache2-utils

Afterwards, we can start htcacheclean as a daemon like this:

htcacheclean -d30 -n -t -p /var/cache/apache2/mod_disk_cache -l 100M -i

This will clean our cache directory every 30 minutes and make sure that it will not get bigger than 100MB. To learn more about htcacheclean, take a look at

man htcacheclean

Of course, you don't want to start htcacheclean manually each time you reboot the server - therefore we edit /etc/rc.local...

vi /etc/rc.local

... and add the following line to it, right before the exit 0 line:

/usr/sbin/htcacheclean -d30 -n -t -p /var/cache/apache2/mod_disk_cache -l 100M -i

This will start htcacheclean automatically each time you start the server.

Falko Timme

About Falko Timme

Falko Timme is an experienced Linux administrator and founder of Timme Hosting, a leading nginx business hosting company in Germany. He is one of the most active authors on HowtoForge since 2005 and one of the core developers of ISPConfig since 2000. He has also contributed to the O'Reilly book "Linux System Administration".

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By: Falko Timme