When host name is omitted, tramp substitutes the value from
tramp-default-host variable. It is initially populated with
the local hostname where Emacs is running. Both the
default user and default host can be overridden as follows:
(setq tramp-default-user "john" tramp-default-host "target")
With both defaults set, ‘/ssh::’ will connect tramp to John's home directory on target.
Note ‘/::’ won't work, because ‘/:’ is the prefix for quoted file names.
Instead of a single default host,
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.
See the documentation for the variable
for more details.