title: How to install extension for php via docker-php-ext-install?
body: <p>In order to <a href="https://stackoverflow.com/questions/37526509/how-to-install-pdo-driver-in-php-docker-image">resolve an issue</a>, I am now trying install the mysql pdo via</p>
  
  <pre><code>docker-php-ext-install
  </code></pre>
  
  <p>as pointed out in the <a href="https://github.com/docker-library/docs/tree/master/php" rel="noreferrer">README of the php image</a>.</p>
  
  <p>Yet my call fails stating:</p>
  
  <pre><code>Libraries have been installed in:
     /usr/src/php/ext/mysqli/modules
  
  If you ever happen to want to link against installed libraries
  in a given directory, LIBDIR, you must either use libtool, and
  specify the full pathname of the library, or use the `-LLIBDIR'
  flag during linking and do at least one of the following:
     - add LIBDIR to the `LD_LIBRARY_PATH' environment variable
       during execution
     - add LIBDIR to the `LD_RUN_PATH' environment variable
       during linking
     - use the `-Wl,--rpath -Wl,LIBDIR' linker flag
     - have your system administrator add LIBDIR to `/etc/ld.so.conf'
  
  See any operating system documentation about shared libraries for
  more information, such as the ld(1) and ld.so(8) manual pages.
  ----------------------------------------------------------------------
  
  Build complete.
  Don't forget to run 'make test'.
  
  Installing shared extensions:     /usr/local/lib/php/extensions/no-debug-non-zts-20131226/
  Installing header files:           /usr/local/include/php/
  find . -name \*.gcno -o -name \*.gcda | xargs rm -f
  find . -name \*.lo -o -name \*.o | xargs rm -f
  find . -name \*.la -o -name \*.a | xargs rm -f 
  find . -name \*.so | xargs rm -f
  find . -name .libs -a -type d|xargs rm -rf
  rm -f libphp.la       modules/* libs/*
  + cd /usr/src/php/ext/mysqlnd
  + phpize
  Cannot find config.m4. 
  Make sure that you run '/usr/local/bin/phpize' in the top level source directory of the module
  
  ERROR: Service 'phlaconapp' failed to build: The command '/bin/sh -c docker-php-ext-install mysqli mysqlnd pdo pdo_mysql zip' returned a non-zero code: 1
  </code></pre>
  
  <p>This is my <code>docker-compose.yml</code>:</p>
  
  <pre><code>phlaconapp:
      hostname: phaclonapp
      dockerfile: Dockerfile
      build: ./
      ports:
          - "1080:80"
          - "1043:433"
      environment:
          TERM: xterm-color
          ENVIRONMENT: dev
      volumes:
          - ./:/var/www/html/
      links:
          - mysql
  mysql:
      image: mysql:5.6
      volumes:
          - ./docker/mysql.d:/etc/mysql/conf.d
      ports: ["3306:3306"]
      environment:
          MYSQL_ROOT_PASSWORD: 'root'
  </code></pre>
  
  <p>This is my <code>Dockerfile</code>:</p>
  
  <pre><code>FROM php:5.6-apache
  
  RUN php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');" &amp;&amp; \
      php -r "if (hash_file('SHA384', 'composer-setup.php') === '070854512ef404f16bac87071a6db9fd9721da1684cd4589b1196c3faf71b9a2682e2311b36a5079825e155ac7ce150d') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;" &amp;&amp; \
      php composer-setup.php &amp;&amp; \
      php -r "unlink('composer-setup.php');"
  
  
  RUN apt-get update &amp;&amp; \
      apt-get install vim git -y
  RUN docker-php-ext-install mysqli mysqlnd pdo pdo_mysql zip 
  
  RUN  cd /  &amp;&amp; \
      git clone --depth=1 git://github.com/phalcon/cphalcon.git &amp;&amp; \
      cd cphalcon/build &amp;&amp; \
      ./install
  
  RUN echo "extension=phalcon.so" &gt; /usr/local/etc/php/conf.d/phalcon.ini
  RUN a2enmod rewrite
  </code></pre>
  
  <p>and running <code>docker-compose build</code> won't finish.</p>