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.Dd November 26, 1997
.Dt HOSTS.EQUIV 5
.Os
.Sh NAME
.Nm hosts.equiv ,
.Nm .rhosts
.Nd trusted remote hosts and host-user pairs
.Sh DESCRIPTION
The
.Nm hosts.equiv
and
.Nm .rhosts
files list hosts and users which are
.Dq trusted
by the local host when a connection is made via
.Xr rlogind 8 ,
.Xr rshd 8 ,
or any other server that uses
.Xr ruserok 3 .
This mechanism bypasses password checks, and is required for access via
.Xr rsh 1 .
.Pp
Each line of these files has the format:
.Pp
.Bd -unfilled -offset indent -compact
hostname [username]
.Ed
.Pp
The
.Em hostname
may be specified as a host name (typically a fully qualified host
name in a DNS environment) or address,
.Dq Li +@netgroup
(from which only the host names are checked),
or a
.Dq Li \&+
wildcard (allow all hosts).
.Pp
The
.Em username ,
if specified, may be given as a user name on the remote host,
.Dq Li +@netgroup
(from which only the user names are checked),
or a
.Dq Li \&+
wildcard (allow all remote users).
.Pp
If a
.Em username
is specified, only that user from the specified host may login to the
local machine.
If a
.Em username
is not specified, any user may login with the same user name.
.Sh EXAMPLES
.Li somehost
.Bd -filled -offset indent -compact
A common usage:  users on
.Em somehost
may login to the local host as the same user name.
.Ed
.Li somehost username
.Bd -filled -offset indent -compact
The user
.Em username
on
.Em somehost
may login to the local host.
If specified in
.Pa /etc/hosts.equiv ,
the user may login with only the same user name.
.Ed
.Li +@anetgroup username
.Bd -filled -offset indent -compact
The user
.Em username
may login to the local host from any machine listed in the netgroup
.Em anetgroup .
.Ed
.Bd -literal -compact
+
+ +
.Ed
.Bd -filled -offset indent -compact
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
.Pa /etc/hosts.equiv ) .
.Ed
.Sh WARNINGS
The username checks provided by this mechanism are
.Em 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.
.Pp
A numeric host address instead of a host name can help security
considerations somewhat; the address is then used directly by
.Xr iruserok 3 .
.Pp
When a username (or netgroup, or +) is specified in
.Pa /etc/hosts.equiv ,
that user (or group of users, or all users, respectively) may login to
the local host as
.Em any local user .
Usernames in
.Pa /etc/hosts.equiv
should therefore be used with extreme caution, or not at all.
.Pp
A
.Pa .rhosts
file must be owned by the user whose home directory it resides in, and
must be writable only by that user.
.Pp
Logins as root only check root's
.Pa .rhosts
file; the
.Pa /etc/hosts.equiv
file is not checked for security.
Access permitted through root's
.Pa .rhosts
file is typically only for
.Xr rsh 1 ,
as root must still login on the console for an interactive login such as
.Xr rlogin 1 .
.Sh FILES
.Bl -tag -width /etc/hosts.equiv -compact
.It Pa /etc/hosts.equiv
Global trusted host-user pairs list
.It Pa ~/.rhosts
Per-user trusted host-user pairs list
.El
.Sh SEE ALSO
.Xr rcp 1 ,
.Xr rlogin 1 ,
.Xr rsh 1 ,
.Xr rcmd 3 ,
.Xr ruserok 3 ,
.Xr netgroup 5
.Sh HISTORY
The
.Nm .rhosts
file format appeared in
.Bx 4.2 .
.Sh BUGS
The
.Xr ruserok 3
implementation currently skips negative entries (preceded with a
.Dq Li \&-
sign) and does not treat them as ``short-circuit'' negative entries.