apt-get install -y php-apc

# configure apc
echo "apc.shm_size=128" >> /etc/php5/conf.d/apc.ini

# configure kernel shm
cat <> /etc/sysctl.conf
kernel.shmall = 134217728
kernel.shmmax = 134217728
EOF
sysctl -p /etc/sysctl.conf

# restart apache
/etc/init.d/apache2 restart

# configure magento to use apc
cp /var/www/app/etc/local.xml.additional  /var/www/app/etc/local.xml.additional.org
diff ./app/etc/local.xml.additional.org ./app/etc/local.xml.additional -Naur
--- ./app/etc/local.xml.additional.org	2011-09-08 11:38:11.000000000 +0200
+++ ./app/etc/local.xml.additional	2011-09-08 11:41:33.000000000 +0200
@@ -35,7 +35,8 @@



-            
+            apc
+            MAGE_





# view APC statistics
gunzip /usr/share/doc/php-apc/apc.php.gz -c > /var/www/apc.php
https://www.example.com/apc.php

# test
/etc/php5/conf.d/apc.ini
#?# apc.ttl=0
#?# apc.mmap_file_mask=/tmp/apc.XXXXXX


# Links
http://magebase.com/magento-tutorials/speeding-up-magento-with-apc-or-memcached/
http://www.squatlabs.com/performance/apc-richtig-konfigurieren
http://www.howtoforge.com/apc-php5-apache2-fedora8