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 checke
If PHP version is 7.2, execute the following command
sudo apt-get install php7.2-xml
Installing xml-extension (php7.0-xml in my case) solved the problem
sudo apt-get install php-xml
DOM is a PHP extension and not a PHP package. This means that your version of PHP needs to be recompiled with the extension. It is possible however that your PHP was already compiled with DOM but that DOM is not enabled.
You can check this in your php.ini (search for extension=dom.so
and make sure it's uncommented).
You might have some missing dependencies, so first run
sudo apt-get -f install
Then install php-xml
sudo apt-get install php-xml
This worked for me.
$ sudo apt-get update
$ sudo apt-get install php5.6-xml
In my case I use
sudo apt-get update
and
sudo apt-get install php7.3-xml