Vagrant + Ubuntu - what is the default username and password to login for the first time?

When we login to Ubuntu for the first time after installation from Vagrant box we need to use:

For Ubuntu 14, CentOS 7:

Default username: root
Default password: vagrant

For Ubunut 16:

Default username: vagrant
Default password: vagrant

Here is wiki post which solve this problem:

Vagrant - default Linux user and password