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

...............................

...............................

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