PHP7.X安装memcached扩展方法,使用于7.0及以上的所有版本。（PHP7.0/PHP7.1/PHP7.2/PHP7.3）
1、安装libmemcached

   
wget https://launchpad.net/libmemcached/1.0/1.0.18/+download/libmemcached-1.0.18.tar.gz
tar zxvf libmemcached-1.0.18.tar.gz
cd libmemcached-1.0.18
./configure --prefix=/usr/local/libmemcached --with-memcached
 make && make install

2、安装php_memcached扩展
支持：php7.0,7.1,7.2,7.3（将目录变更为自己的php安装目录）

   
    wget http://pecl.php.net/get/memcached-3.1.5.tgz
    tar zxvf memcached-3.1.5.tgz
    cd memcached-3.1.5
    ./configure --with-php-config=/usr/php7.2/bin/php-config --enable-memcached --enable-memcached-json  --with-libmemcached-dir=/usr/local/libmemcached/
    make
    cp modules/memcached.so /usr/php7.2/modules/
    echo 'extension=memcached.so' >>/etc/php7.2/php.ini