Na maior parte do tempo, você usará ssh . vncviewer pode estar disponível, mas geralmente não é (a maioria dos servidores não terá X11 ou qualquer coisa relacionada a gráficos).
Por que usar o SSH? A partir da documentação do CentOS :
After an initial connection, the client can verify that it is connecting to the same server it had connected to previously.
The client transmits its authentication information to the server using strong, 128-bit encryption.
All data sent and received during a session is transferred using 128-bit encryption, making intercepted transmissions extremely difficult to decrypt and read.
The client can forward X11 applications from the server. This technique, called X11 forwarding, provides a secure means to use graphical applications over a network.