ERROR: The directory [/storage/...] must be writable

If you get the error below:

ERROR: The directory [/bootstrap/cache] must be writable by the web server.
ERROR: The directory [/storage/app] must be writable by the web server.
ERROR: The directory [/storage/framework] must be writable by the web server.
ERROR: The directory [/storage/logs] must be writable by the web server.

This is mind that you have not give the right permissions to the "storage/" folder and to its subfolders. So, you need to give a read & write permission recursively for all the system users (755 or 777 recursively).