Unable to upgrade from version 5.10.0 to version 8 I tried upgrading from Drush 5.10.0 to Drush 8 using sudo composer global require drush/drush:~8, but it doesn't update anything.


  Changed current directory to /home/lupiyardo/.composer
  Running composer as root/super user is highly discouraged as packages, plugins and scripts cannot always be trusted
  ./composer.json has been updated
  Loading composer repositories with package information
  Updating dependencies (including require-dev)
  Nothing to install or update
  Generating autoload files


As confirmation Drush wasn't updated, the output of drush --version is Drush 5.10.0.

I looked at the composer.json file and it contains 'require': { }. 

How can I upgrade Drush?
The following code works for me in Linux Machine:
    cd /usr/local/bin
    mkdir drush-8
    cd drush-8
    composer require drush/drush:8.x
    ln -s /usr/local/bin/drush-8/vendor/bin/drush /usr/local/bin/drush8

Let me explain a little bit:


Go to folder /usr/local/bin   
Create a new folder drush-8  * go
to the folder above  
Install drush (here more info:
https://docs.drush.org/en/master/install/ )  
Finally, create a Symbolic Links that point to new drush version