这个问题之前就遇到过，记得最后是通过下载源码包来指定路径的，今天又从新安装环境结果一定要试试，因为我知道只要安装这种libmemcached-devdev包就一定有头文件，结果最后通过查询资料真的让我找到了，以下记录这个过程

首先安装依赖以编译安装

sudo apt-get install libmemcached libmemcached-devpecl download memcached
tar zxvf memcached.tar.gz
cd memcached
phpize./configure --with-libmemcached-dir=这个目录可使用如下命令查找123456

dpkg -L libmemcached-dev | grep memcached.h

/usr/include/libmemcached-1.0/memcached.hpp
/usr/include/libmemcached-1.0/struct/memcached.h
/usr/include/libmemcached-1.0/memcached.h
/usr/include/libmemcached/memcached.hpp
/usr/include/libmemcached/memcached.h12345

这样明明看到了memcached.h文件了，那么路径就写成/usr/include/libmemcached可是不行，保错

./configure --with-libmemcached-dir=/usr/include/libmemcached

checking for libmemcached location... configure: error: Unable to find memcached.h under /u/weiz/libmemcached-1.0.16123

通过查看 
https://github.com/php-memcached-dev/php-memcached/blob/master/config.m4#L277 
可以看到 
if test ! -f "$PHP_LIBMEMCACHED_DIR/include/libmemcached/memcached.h"; 
原来他要去这个路径include/libmemcached/下寻找，难怪出错

接下来执行

sudo mkdir -p /usr/lib/x86_64-linux-gnu/include/libmemcached
sudo ln -s /usr/include/libmemcached/memcached.h /usr/lib/x86_64-linux-gnu/include/libmemcached/memcached.h12

接下来在执行就好了

sudo ./configure --with-php-config=/usr/local/php/bin/php-config --enable-memcached --with-libmemcached-dir=/usr/lib/x86_64-linux-gnu --disable-memcached-saslsudo make
sudo make install