How to install mcrypt PHP module on Ubuntu 18.04 Linux

How to install mcrypt PHP module on Ubuntu 18.04 Linux
Lubos RendekSystem Administration14 November 2018
# Objective
The objective is to install mcrypt PHP module on Ubuntu 18.04 Linux
# Operating System and Software Versions
Operating System: - Ubuntu 18.04 Linux
Software: - PHP 7.2 or higher
# Requirements
Privileged access to your Ubuntu System as root or via sudo command is required.
# Difficulty
EASY
# Conventions
 - requires given linux commands to be executed with root privileges either directly as a root user or by use of sudo command
$ - given linux commands to be executed as a regular non-privileged user
# Instructions
## PHP installation
Most likely you PHP is already installed but any attempt to install the mcrypt PHP module fails with an error message:
E: Package 'php-mcrypt' has no installation candidate
If this is so, simply skip this step. Alternatively, perform a basic PHP installation:
$ sudo apt install php
Next, check whether the mcrypt PHP module is present:
$ php -m | grep mcrypt
## Install Prerequisites
To install the mcrypt PHP module we first need to satisfy the following prerequisites:
$ sudo apt install php-dev libmcrypt-dev php-pear
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## Install mcrypt PHP module
Now we are ready to install mcrypt PHP module on our Ubuntu 18.04 system:
$ sudo pecl channel-update pecl.php.net
$ sudo pecl install mcrypt-1.0.1
...
Build process completed successfully
Installing '/usr/lib/php/20170718/mcrypt.so'
install ok: channel://pecl.php.net/mcrypt-1.0.1
configuration option "php_ini" is not set to php.ini location
You should add "extension=mcrypt.so" to php.ini
Lastly, as suggested by the compilation output we need to enable the mcrypt PHP module within appropriate php.ini file. Your configuration may be different, the below serves only as a solution to the default PHP CLI configuration. Open the /etc/php/7.2/cli/php.ini file and insert:
extension=mcrypt.so
Please note that if you are using Apache or Nginx web-server or another PHP version the location of the loaded php.ini file may be different.

All done. When successful, checking for the presence of the mcrypt PHP module should produce the following output:
$ php -m | grep mcrypt
mcrypt