Via libguestfs-tools ( view http://bderzhavets.blogspot.com/2014/... )
You can cat /etc/cloud/cloud.cfg and see default user-name (ubuntu,fedora,centos,cloud-user,....). If instance was launched with ssh key pair oskey.pem ( for instance), then login (with no password) :

$ ssh -i oskey.pem default-user-name@floating-ip

Users can only ssh to the instance by using the admin password if:

The virtual machine image is a Linux distribution

The virtual machine has been configured to allow users to ssh as the root user. This is not the case for Ubuntu cloud images, which disallow ssh to the root account by default.

Ref:- http://docs.openstack.org/admin-guide...