由于zend optimizer不支持php5.3，使用php5.3以上版本就要安装zend guard loader。
参考：http://amon.org/zend-optimizer
PHP 5.5：Zend Guard Loader for PHP 5.5
PHP 5.6：Zend Guard Loader for PHP 5.6
PHP 5.2 files encoded with Zend Guard 5.0 or Zend Guard 5.5 require Zend Optimizer as the runtime decoder.
【Atomic库安装】
参考：http://www.laozuo.org/1940.html
Atomic源支持Fedora，RHEL和CentOS的YUM包管理。
清单：http://www.atomicorp.com/channels/atomic/
需要先安装Atomic库，然后安装zend-guard-loader：
wget -q -O - http://www.atomicorp.com/installers/atomic | sh
yum install php-zend-guard-loader
安装完后在 /etc/yum.repos.d/ 目录会有一个 atomic.repo 文件。
【源码安装】
下载：http://www.zend.com/en/products/loader/downloads
参考：http://files.zend.com/help/Zend-Guard/content/installing_zend_guard_loader.htm
参考：http://www.cnblogs.com/qiandu/p/4201456
参考：https://serverpilot.io/community/articles/how-to-install-zend-guard-loader
参考：http://blog.chinaunix.net/uid-14735472-id-3764932
参考：http://jingyan.baidu.com/article/ceb9fb10dae0d98cad2ba005
参考：http://dedecms.com/knowledge/servers/linux-bsd/2012/0819/8491
wget http://downloads.zend.com/guard/7.0.0/zend-loader-php5.5-linux-x86_64_update1.tar.gz && tar zxvf zend-loader-php5.5-linux-x86_64_update1.tar.gz
cp -R zend-loader-php5.5-linux-x86_64/ /usr/local/zend/
编辑 php.ini ，在最后位置添加：
[Zend Guard]
zend_extension=/usr/local/zend/ZendGuardLoader.so
zend_loader.enable=1
zend_loader.disable_licensing=0
zend_loader.obfuscation_level_support=3
zend_loader.license_path=
查证：
php -i | grep "Zend Guard Loader"
报错：
Failed loading /usr/local/php/lib/php/extensions/zend-loader-php5.5-linux-x86_64/ZendGuardLoader.so: /usr/local/php/lib/php/extensions/zend-loader-php5.5-linux-x86_64/ZendGuardLoader.so: undefined symbol: executor_globals
参考：http://www.verydemo.com/demo_c101_i53243
参考：http://forums.zend.com/viewtopic.php?t=22958
参考：http://smilejay.com/2013/05/apache-mpm/
参考：http://www.aichengxu.com/view/934944
apache有两种运行模式：prefork模式；worker模式。区别请看：http://bbs.ywlm.net/thread-919-1-1
–with-mpm=worker 即worker模式，很多第三方模块不支持的
–with-mpm=prefork 重新编译apache就OK了。
如果用yum安装的，默认用的是prefork模式，这是为了兼容性。
参考：http://files.zend.com/help/Zend-Guard/content/installing_zend_guard_loader.htm
参考：http://www.phpfans.net/ask/question2/2455115949
参考：http://forums.zend.com/viewtopic.php?t=126063
Zend Guard Loader requires PHP NTS (non-thread-safe) and when loaded under Apache, use Prefork MPM.
参考：http://stackoverflow.com/questions/22201013/error-failed-loading-opcache-so-opcache-so-undefined-symbol-compiler-globals
参考：http://stackoverflow.com/questions/13883646/apache-prefork-vs-worker-mpm
You’re using Apache2 MPM. So PHP builds an ZTS (Zend Threaded System) build. See Apache Prefork vs Worker MPM for a discussion on this. With MPM PHP stores its compiler globals in a thread array. However, OPcache is looking for the non-threaded version of this structure compiler_globals.
IMO, if you are using a PHP, then using MPM is a mistake as (i) the PHP runs ~25-50% slower, (ii) many extension don’t work; (iii) OPcache isn’t properly tested with ZTS builds. Stick to a Prefork worker configuration, and rebuild.
以 –with-mpm=prefork 参数重新编译安装Apache2：
./configure --prefix=/usr/local/apache2 --enable-mods-shared=most --with-mpm=prefork --with-crypto --enable-rewrite --enable-headers --enable-deflate --enable-socache-shmcb --enable-negotiation --enable-ssl --with-ssl=/usr/lib --enable-http2 --with-nghttp2=/usr/local/lib
查看当前apache中已经编译了的模块：
service httpd -l
输出：
Compiled in modules:
core.c
mod_so.c
http_core.c
prefork.c
由于MPM只能在编译时指定其中一种，所以列出的静态模块中MPM只有1个：
查看httpd加载的所有模块（包括静态编译的和动态共享的模块）：
service httpd -t -D DUMP_MODULES
输出：
Loaded Modules:
core_module (static)
so_module (static)
http_module (static)
mpm_prefork_module (static)
authn_file_module (shared)
authn_core_module (shared)
authz_host_module (shared)
authz_groupfile_module (shared)
authz_user_module (shared)
authz_core_module (shared)
access_compat_module (shared)
auth_basic_module (shared)
reqtimeout_module (shared)
filter_module (shared)
mime_module (shared)
log_config_module (shared)
env_module (shared)
headers_module (shared)
setenvif_module (shared)
version_module (shared)
unixd_module (shared)
status_module (shared)
autoindex_module (shared)
cgi_module (shared)
dir_module (shared)
alias_module (shared)
cgid_module (shared)
php5_module (shared)
查看 httpd.conf，有关于 mpm 模式的设置：
# Server-pool management (MPM specific)
#Include conf/extra/httpd-mpm.conf
conf/extra/httpd-mpm.conf 的对应设置：
# prefork MPM
# StartServers: number of server processes to start
# MinSpareServers: minimum number of server processes which are kept spare
# MaxSpareServers: maximum number of server processes which are kept spare
# MaxRequestWorkers: maximum number of server processes allowed to start
# MaxConnectionsPerChild: maximum number of connections a server process serves
# before terminating
<IfModule mpm_prefork_module>
StartServers 5
MinSpareServers 5
MaxSpareServers 10
MaxRequestWorkers 250
MaxConnectionsPerChild 0
</IfModule>
参考：https://smyl.es/how-to-fix-ioncubezendguard-undefined-symbol-executor_globals-after-upgrading-apache-and-php/
参考：http://stackoverflow.com/questions/17272439/how-to-enable-zts-on-php
参考：https://github.com/krakjoe/pthreads/issues/436
重新编译安装PHP
重新安装ZendOptimizer
在程序都重新编译安装完后，重启Apache，就可以了
输出：
with Zend Guard Loader v3.3, Copyright (c) 1998-2014, by Zend Technologies
Zend Guard Loader
Zend Guard Loader => enabled
部署zend guard
实证未遂。
参考：http://files.zend.com/help/Zend-Guard/content/install.htm
参考：http://static.zend.com/topics/Zend-Guard-Release-Notes-v5-5.txt
下载：http://www.zend.com/en/products/guard/downloads
http://downloads.zend.com/guard/7.0.0/ZendGuard-7.0.0-linux.gtk.x86_64.tar.gz
http://downloads.zend.com/guard/6.0.0/ZendGuard-6_0_0-linux.tar.gz
http://downloads.zend.com/guard/5.5.0/ZendGuard-5_5_0.tar.gz
wget http://downloads.zend.com/guard/5.5.0/ZendGuard-5_5_0.tar.gz && tar zxvf ZendGuard-5_5_0.tar.gz && ./ZendGuard-5_5_0.bin
