rlogin-process-connection-type

rlogin-process-connection-type is a variable defined in `rlogin.el'.
Its value is

nil

Documentation:
If non-nil, use a pty for the local rlogin process.
If nil, use a pipe (if pipes are supported on the local system).

Generally it is better not to waste ptys on systems which have a static
number of them. On the other hand, some implementations of `rlogin' assume
a pty is being used, and errors will result from using a pipe instead.

You can customize this variable.