I try to install mcrypt in my docker image based on php:7.2-apache. Therefore I use the RUN-Command from the documentation and also answerd here but I receive this error:
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 && apt-get install -y          libfreetype6-dev          libjpeg62-turbo-dev          libmcrypt-dev          libpng-dev     && docker-php-ext-install -j$(nproc) iconv mcrypt gd mbstring zip' returned a non-zero code: 1   My Dockerfile:
FROM php:7.2-apache  RUN apt-get update && apt-get install -y \      libfreetype6-dev \      libjpeg62-turbo-dev \      libmcrypt-dev \      libpng-dev \ && docker-php-ext-install -j$(nproc) iconv mcrypt gd mbstring zip #    && docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/ \ #    && docker-php-ext-install -j$(nproc) gd   COPY ./etc/000-default.conf /etc/apache2/sites-available/  EXPOSE 80   Has anybody an idea how to solve or how to get the needed files in the requested folder?
Thanks!
docker-php-source We just take it as a storage directory of PHP extension source code downloaded from the Internet. In fact, all PHP extension source code extensions are stored in the path: / usr/src/php/ext.
The mcrypt extension is an interface to the mcrypt cryptography library. This extension is useful for allowing PHP code using mcrypt to run on PHP 7.2+. The mcrypt extension is included in PHP 5.4 through PHP 7.1.
docker-php-ext-install - build extension from source, usually executes docker-php-ext-configure for build configuration, enables the extension (php.ini entry) by executing docker-php-ext-enable after all. docker-php-ext-enable - enables an already extension by adding a specific entry to php. ini.
mcrypt extension is not provided with the PHP source since 7.2 , but are instead available through PECL. To install a PECL extension in docker, use pecl install to download and compile it, then use docker-php-ext-enable to enable it:
pecl install mcrypt-1.0.4 docker-php-ext-enable mcrypt  Before the pecl install you may need to install/update the package libmcrypt-dev
apt-get update && apt-get install -y libmcrypt-dev 
                        Building on MoiioM's answer, this worked for me using the 7.2-stretch Docker image from PHP
RUN apt-get update && apt-get install -y libmcrypt-dev \     && pecl install mcrypt-1.0.4 \     && docker-php-ext-enable mcrypt 
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