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HOSTS.EQUIV(5)                             BSD File Formats Manual                            HOSTS.EQUIV(5)

NAME
     hosts.equiv, .rhosts -- trusted remote hosts and host-user pairs

DESCRIPTION
     The hosts.equiv and .rhosts files list hosts and users which are ``trusted'' by the local host when a
     connection is made via rlogind(8), rshd(8), or any other server that uses ruserok(3).  This mechanism
     bypasses password checks, and is required for access via rsh(1).

     Each line of these files has the format:

           hostname [username]

     The hostname may be specified as a host name (typically a fully qualified host name in a DNS environ-ment) environment)
     ment) or address, +@netgroup (from which only the host names are checked), or a ``+'' wildcard (allow
     all hosts).

     The username, if specified, may be given as a user name on the remote host, +@netgroup (from which only
     the user names are checked), or a ``+'' wildcard (allow all remote users).

     If a username is specified, only that user from the specified host may login to the local machine.  If
     a username is not specified, any user may login with the same user name.

EXAMPLES
     somehost
           A common usage:  users on somehost may login to the local host as the same user name.
     somehost username
           The user username on somehost may login to the local host.  If specified in /etc/hosts.equiv, the
           user may login with only the same user name.
     +@anetgroup username
           The user username may login to the local host from any machine listed in the netgroup  anetgroup.
     +
     + +
           Two  severe  security  hazards.   In the first case, allows a user on any machine to login to the
           local host as the same user name.  In the second case, allows any user on any machine to login to
           the local host (as any user, if in /etc/hosts.equiv).

WARNINGS
     The username checks provided by this mechanism are not secure, as the remote user name is received by
     the server unchecked for validity.  Therefore this mechanism should only be used in an environment
     where all hosts are completely trusted.

     A numeric host address instead of a host name can help security considerations somewhat; the address is
     then used directly by iruserok(3).

     When a username (or netgroup, or +) is specified in /etc/hosts.equiv, that user (or group of users, or
     all users, respectively) may login to the local host as any local user.  Usernames in /etc/hosts.equiv
     should therefore be used with extreme caution, or not at all.

     A .rhosts file must be owned by the user whose home directory it resides in, and must be writable only
     by that user.

     Logins as root only check root's .rhosts file; the /etc/hosts.equiv file is not checked for security.
     Access permitted through root's .rhosts file is typically only for rsh(1), as root must still login on
     the console for an interactive login such as rlogin(1).

FILES
     /etc/hosts.equiv  Global trusted host-user pairs list
     ~/.rhosts         Per-user trusted host-user pairs list

SEE ALSO
     rcp(1), rlogin(1), rsh(1), rcmd(3), ruserok(3), netgroup(5)

HISTORY
     The .rhosts file format appeared in 4.2BSD.

BUGS
     The ruserok(3) implementation currently skips negative entries (preceded with a ``-'' sign) and does
     not treat them as ``short-circuit'' negative entries.

BSD                                           November 26, 1997                                          BSD