title: Docker-php-ext-install mcrypt missing folder
body: <p>I try to install mcrypt in my docker image based on <code>php:7.2-apache</code>. Therefore I use the RUN-Command from the documentation and also answerd <a href="https://stackoverflow.com/questions/47181369/how-to-install-mcrypt-on-docker">here</a> but I receive this error:</p>
  
  <pre><code>error: /usr/src/php/ext/mcrypt does not exist
  
  
  usage: /usr/local/bin/docker-php-ext-install [-jN] ext-name [ext-name ...]
  
     ie: /usr/local/bin/docker-php-ext-install gd mysqli
     /usr/local/bin/docker-php-ext-install pdo pdo_mysql
     /usr/local/bin/docker-php-ext-install -j5 gd mbstring mysqli pdo pdo_mysql shmop
  
  if custom ./configure arguments are necessary, see docker-php-ext-configure
  
  Possible values for ext-name:
  bcmath bz2 calendar ctype curl dba dom enchant exif fileinfo filter ftp  gd gettext gmp hash iconv imap interbase intl json ldap mbstring mysqli oci8  odbc opcache pcntl pdo pdo_dblib pdo_firebird pdo_mysql pdo_oci pdo_odbc pdo_pgsql pdo_sqlite pgsql phar posix pspell readline recode reflection session shmop simplexml snmp soap sockets sodium spl standard sysvmsg sysvsem sysvshm tidy tokenizer wddx xml xmlreader xmlrpc xmlwriter xsl zend_test zip
  
  Some of the above modules are already compiled into PHP; please check
  the output of "php -i" to see which modules are already loaded.
  ERROR: Service 'web' failed to build: The command '/bin/sh -c apt-get update &amp;&amp; apt-get install -y          libfreetype6-dev          libjpeg62-turbo-dev          libmcrypt-dev          libpng-dev     &amp;&amp; docker-php-ext-install -j$(nproc) iconv mcrypt gd mbstring zip' returned a non-zero code: 1
  </code></pre>
  
  <p>My Dockerfile:</p>
  
  <pre><code>FROM php:7.2-apache
  
  RUN apt-get update &amp;&amp; apt-get install -y \
       libfreetype6-dev \
       libjpeg62-turbo-dev \
       libmcrypt-dev \
       libpng-dev \
  &amp;&amp; docker-php-ext-install -j$(nproc) iconv mcrypt gd mbstring zip
  #    &amp;&amp; docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/ \
  #    &amp;&amp; docker-php-ext-install -j$(nproc) gd
  
  
  COPY ./etc/000-default.conf /etc/apache2/sites-available/
  
  EXPOSE 80
  </code></pre>
  
  <p>Has anybody an idea how to solve or how to get the needed files in the requested folder?</p>
  
  <p>Thanks!</p>