By default it’s not possible to establish a direct SSH connection to a Proxmox’s default Ubuntu 14.x or 16.x LXC VPS.
In order to SSH into a Ubuntu 14.x and 16.x LXC VPS you need to use NoVNC Console to apply following commands:
Modify /etc/ssh/sshd_config
nano /etc/ssh/sshd_config
Change Config
PermitRootLogin without-password to PermitRootLogin yes
Restart SSH Service
service ssh restart