There are no commands defined in the "setup" namespace : Magento 2

Please mention setup_version in your module.xml file. Your module.xml file looks like:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../../../../lib/internal/Magento/Framework/Module/etc/module.xsd">
  <module name="Vendor_Module" setup_version="1.0.0"/> 
</config>

You need to give full permission to both var and pub folders recursively.

sudo chmod -R 777 var pub

I wanted to add an answer because the others doens't cover all the problems that could generate this error :

There are no commands defined in the "setup" namespace.

in general.

This error could be caused by permission as said in others answer but we could have other scenario.

• The absense of : etc/module.xml
• An error in /etc/module.xml or in /etc/di.xml or others xml extensions under /etc
  

If you know other scenario please comment this answer.
Hope this help.

Giving full control (read/write/execute) to var and pub directory should solve this issue.

sudo chmod -R 777 var pub

You may also try running the command using sudo.

sudo php bin/magento setup:upgrade