specify trusted hosts and users
/etc/host.equiv
The host.equiv file is used to specify to the “r” utilities that users need to authenticate themselves with a password. By default, all users are not trusted, which means a password is required.
The format of the host.equiv file is a list of entries, one per line. Each entry is formatted as follows:
[+|-][hostname] [[+|-]user [[+|-]user ...]]
where hostname is the name of a host, followed by an optional list of user. The + and - signs are used to explicitly specify if password-free access should be permitted:
For example configurations and a detailed discussion of the security issues involved, refer to Hunt's TCP/IP Network Administration, pp. 193-195.