RockMongo, "Unable to load dynamic library '/.../mongo.so' - wrong ELF class: ELFCLASS64 in Unknown"

I just installed RockMongo by extracting all the files to a lampp web folder /opt/lampp/htdocs/rockMongo/. Visiting index.php shows

To make things right, you must install php_mongo module. Here for installation documents on PHP.net.

I followed the instructions there (I had to install php-pear):

• sudo pecl install mongo
• Add the following line to php.ini: extension=mongo.so

Now, when I start the web server (apache), I get the following warning, repeated hundreds of times:

Warning: PHP Startup: It is not safe to rely on the system's timezone settings. You are required to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EDT/-4.0/DST' instead in Unknown on line 0

and also this warning a single time:

Warning: PHP Startup: Unable to load dynamic library '/usr/lib/php5/20090626/mongo.so' - /usr/lib/php5/20090626/mongo.so: wrong开发者_StackOverflow社区 ELF class: ELFCLASS64 in Unknown on line 0

The index page stills shows the same message (which means that class_exists("Mongo") returns false)

I tried putting in the absolute path to mongo.so, but that didn't do anything. What's going on?

edit: I used

$ file /usr/bin/php5
/usr/bin/php5: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.15, stripped

which seems to suggest my php installation is 64 bits, yet when I print out PHP_INT_MAX I get 2147483647 which seems to indicate my installation is 32 bits. How can I know the "bitness" of my php installation?

From the second PHP warning, it looks like you've mixed 32bit code and a 64bit library.

Make sure all the stuff you've downloaded is of the same "bitness" as your PHP installation.