Installing the ssdeep PECL extension
After you have installed a copy of ssdeep (see below for more information) you simply run the following command:
sudo pecl install ssdeep
Installing the ssdeep libraries
I would recommend building ssdeep from source using the instructions from it's project site.
Once done you need to copy .libs/* to /usr/lib so that the php_ssdeep extension can see the ssdeep libraries.
sudo cp .libs/* /usr/lib
You can use the packages supplied with Ubuntu or Debian, but they are not yet updated to the latest version of ssdeep.
If you are having trouble building or running the php_ssdeep extension it expects to see the following directory structure:
/usr/bin/ssdeep
/usr/include/fuzzy.h
/usr/lib/libfuzzy.a
/usr/lib/libfuzzy.la
/usr/lib/libfuzzy.so
/usr/lib/libfuzzy.so.2
/usr/lib/libfuzzy.so.2.0.0
Source: Ubuntu Karmic File List
If this still does not resolve the problem then uninstall the ssdeep pecl extension:
pecl uninstall ssdeep
And re-install the extension specifying the path to the ssdeep libraries:
LD_LIBRARY_PATH=/usr/lib/:$LD_LIBRARY_PATH pecl install ssdeep
Where /usr/lib/ is the directory containing the fuzzy libraries installed earlier.