Manual:Oracle

Some linux distros have packages for installing this, but not all ...

Installing Oracle XE on linux (manually)
Oracle XE is an entry level database free of charge but with embeded limitations:
 * will use only CPU resources that are equivalent of 1 CPU/core on your system
 * will use only up to 1G or RAM
 * is limited to 1 server/database instance per machine
 * is limited to 11G of user-space data

Follow the installation procedure is described in the XE installation manual.

If you use a distro like Ubuntu a good manual for most cases (not only Ubuntu 11.10) can be found at oracle forum

'''If you're installing this DB for occasional use MAKE SURE you set it up so it will not start at boot. This DB goes trough resources like the CookieMonster trough Bahlsen factory'''

Some basic DBA commands can be found on XE DBA Documentation page but in most cases you can use DB control interface that can be accessed trough DB's http port (the one you selected when you ran "oracle-xe configure")

Installing Oracle Instant Client on linux (manually)
Follow the instructions found at Oracle's PHP documentation page. '''The only thing you SHOULD do differently is instead of using PECL extension, you should use oci from PHP source. PECL usually is more recent, but also more unstable. Just a suggestion.'''

After you have your PHP env set up, add TNS_ADMIN variable to your PHP startup env. This variable must contain the location (directory only) where your tnsnames.ora file is located. This file contains TNS definitions of the databases you will be accessing (local or remote). If you have previously set up XE on this machine this variable should point to '/u01/app/oracle/product/11.2.0/xe/network/admin' (default location).

Installing MediaWiki
After you have OCI8 enabled and TNS_ADMIN set in your PHP env you can now install MW normally. TNS name of default XE install is usually 'XE'.

Test drive your wiki ...