1、因为php_memcached是依赖libmemcached库，所以首先安装libmemcached库，需要安装libmemcached-1.x以上版本
wget https://launchpad.net/libmemcached/1.0/1.0.16/+download/libmemcached-1.0.16.tar.gz
tar -zxvf libmemcached-1.0.16.tar.gz
cd libmemcached-1.0.16
./configure -prefix=/usr/local/libmemcached
make && make install
2.安装扩展，这里我们使用php自带的pecl命令来安装php扩展。
/usr/local/webserver/php/bin/pecl install memcached
WARNING: channel "pecl.php.net" has updated its protocols, use "pecl channel-update pecl.php.net" to update
downloading memcached-2.2.0.tgz ...
Starting to download memcached-2.2.0.tgz (70,449 bytes)
.................done: 70,449 bytes
15 source files, building
running: phpize
Configuring for:
PHP Api Version: 20121113
Zend Module Api No: 20121212
Zend Extension Api No: 220121212
libmemcached directory [no] : /usr/local/libmemcached
building in /tmp/pear/temp/pear-build-rootjTskoD/memcached-2.2.0
running: /tmp/pear/temp/memcached/configure --with-libmemcached-dir=/usr/local/libmemcached
...............................
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3、安装完成后在配置文件添加
vim /usr/local/webserver/php/etc/php.ini
extension=memcached.so
4.重启web服务器
service nginx restart
5.重启php
service php-fpm restart
6.验证
php -m|grep memcache
memcache
memcached
