laravel composer update : the requested PHP extension dom is missing from your system

Question

I am using ubuntu 16.04, laravel 5.2 when i run update composer in my project directory its showing "the requested PHP extension dom is missing from your system" i checked installed packages of PHP, its available there

Answer 1

Installing xml-extension (php7.0-xml in my case) solved the problem

sudo apt-get install php-xml

Answer 2

If PHP version is 7.2, execute the following command

sudo apt-get install php7.2-xml

Answer 3

Managed to fix it with a php version 5.6* :

$ sudo apt-get update
$ sudo apt-get install php5.6-xml