When host name is omitted, Tramp substitutes the value from the tramp-default-host user option. It is initially populated with the local host name where Emacs is running. The default method, default user and default host can be overridden as follows:(custom-set-variables '(tramp-default-method "ssh") '(tramp-default-user "john") '(tramp-default-host "target"))
With all defaults set, ‘/-::’ will connect Tramp to John's home directory on
Instead of a single default host, tramp-default-host-alist allows multiple default host values based on access method or user name combinations. The alist can hold multiple values. While tramp-default-host is sufficient in most cases, some methods, like adb, require defaults overwritten.