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 environment) 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 consider‐
ations 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 con‐
sole 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 ALSOrcp(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
