Is the host localhost always available for the own system?

localhost, ping

Solution

Any correct implementation of TCP/IP will reserve the address 127.0.0.1 to refer to the local machine. However, the mapping of the name "localhost" to that address is generally dependent on the system `hosts` file. If you were to remove the localhost entry from `hosts`, then the localhost name may no longer resolve properly at all.

Problem

Is it always possible to ping localhost and it resolves to 127.0.0.1? I know Windows Vista, XP, Ubuntu and Debian do it but does everyone do it?

Original source