How to install Composer on Debian / Ubuntu Linux

Posted on in Categories , , , , last updated August 2, 2016

I‘m trying to upgrade my Mediawiki installation and I’m getting an error that read as follows:
    Error: your composer.lock file is not up to date, run “composer update” to install newer dependencies
How do I install composer command for my PHP installation on Debian or Ubuntu Linux running LAMP or LEMP stack? How do I Install and use Composer on running Ubuntu Linux server and fix this problem for mediawiki installation and/or manage and install PHP packages and dependencies for my project?