PHP 5.3.5 (cli) (built: Feb 19 2011 17:58:43)
Copyright (c) 1997-2010 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2010 Zend Technologies
    with XCache v1.3.1, Copyright (c) 2005-2010, by mOo

nginx + php-fpm работает xcache
nginx (прокси) + apache22 + libphp5.so НЕ работает xcache

в phpinfo он и там и там работает, в логах ошибок нет

nginx-0.8.54        Robust and small WWW server
xcache-1.3.1        A fast and stable php opcode cacher
apache-itk-2.2.17_1 Version 2.2.x of Apache web server with itk MPM.
php5-5.3.5          PHP Scripting Language
php5-bcmath-5.3.5   The bcmath shared extension for php
php5-bz2-5.3.5      The bz2 shared extension for php
php5-calendar-5.3.5 The calendar shared extension for php
php5-ctype-5.3.5    The ctype shared extension for php
php5-curl-5.3.5     The curl shared extension for php
php5-dom-5.3.5      The dom shared extension for php
php5-extensions-1.4 A "meta-port" to install PHP extensions
php5-filter-5.3.5   The filter shared extension for php
php5-ftp-5.3.5      The ftp shared extension for php
php5-gd-5.3.5       The gd shared extension for php
php5-gettext-5.3.5  The gettext shared extension for php
php5-gmp-5.3.5      The gmp shared extension for php
php5-hash-5.3.5     The hash shared extension for php
php5-iconv-5.3.5    The iconv shared extension for php
php5-json-5.3.5     The json shared extension for php
php5-mbstring-5.3.5 The mbstring shared extension for php
php5-mcrypt-5.3.5   The mcrypt shared extension for php
php5-mysql-5.3.5    The mysql shared extension for php
php5-mysqli-5.3.5   The mysqli shared extension for php
php5-openssl-5.3.5  The openssl shared extension for php
php5-pcntl-5.3.5    The pcntl shared extension for php
php5-pdo-5.3.5      The pdo shared extension for php
php5-pdo_sqlite-5.3.5 The pdo_sqlite shared extension for php
php5-posix-5.3.5    The posix shared extension for php
php5-pspell-5.3.5   The pspell shared extension for php
php5-recode-5.3.5   The recode shared extension for php
php5-session-5.3.5  The session shared extension for php
php5-shmop-5.3.5    The shmop shared extension for php
php5-simplexml-5.3.5 The simplexml shared extension for php
php5-snmp-5.3.5     The snmp shared extension for php
php5-sockets-5.3.5  The sockets shared extension for php
php5-sqlite-5.3.5   The sqlite shared extension for php
php5-sysvmsg-5.3.5  The sysvmsg shared extension for php
php5-sysvsem-5.3.5  The sysvsem shared extension for php
php5-sysvshm-5.3.5  The sysvshm shared extension for php
php5-tidy-5.3.5     The tidy shared extension for php
php5-tokenizer-5.3.5 The tokenizer shared extension for php
php5-wddx-5.3.5     The wddx shared extension for php
php5-xml-5.3.5      The xml shared extension for php
php5-xmlreader-5.3.5 The xmlreader shared extension for php
php5-xmlrpc-5.3.5   The xmlrpc shared extension for php
php5-xmlwriter-5.3.5 The xmlwriter shared extension for php
php5-xsl-5.3.5      The xsl shared extension for php
php5-zip-5.3.5      The zip shared extension for php
php5-zlib-5.3.5     The zlib shared extension for php