HOSTS.EQUIV(5)

NAME
hosts.equiv, .rhosts - trusted remote hosts and users

DESCRIPTION

The /etc/hosts.equiv and .rhosts files provide the ``remote authentication'' database for rlogin(1C), rsh(1C), rcp(1C), and rcmd(3N). The files specify remote hosts and users that are considered trusted. Trusted users are allowed to access the local system without supplying a password. The library routine ruserok() (see rcmd(3N)) performs the authentication procedure for programs by using the /etc/hosts.equiv and .rhosts files. The /etc/hosts.equiv file applies to the entire system, while individual users can maintain their own .rhosts files in their home directories.

These files bypass the standard password-based user authentication mechanism. To maintain system security, care must be taken in creating and maintaining these files.

The remote authentication procedure determines whether a particular remote user from a particular remote host should be allowed to access the local system as a (possibly different) particular local user. This procedure first checks the /etc/hosts.equiv file and then checks the .rhosts file in the home directory of the local user as whom access is being attempted. Entries in these files can be of two forms. Positive entries explicitly allow access, while negative entries explicitly deny access. The authentication succeeds as soon as a matching positive entry is found. The procedure fails when a matching negative entry is found, or if no matching entries are found in either file. The order of entries, therefore, can be important: If the files contain both matching positive and negative entries, the entry that appears first will prevail. The rsh(1C) and rcp(1C) programs fail if the remote authentication procedure fails. The rlogin program will fall back to the standard password-based login procedure if the remote authentication fails.

Both files are formatted as a list of one-line entries. Each entry has the form:

    hostname [username]

Negative entries are differentiated from positive entries by a `-' character preceding either the hostname or username field.

  Positive Entries

If the form:

    hostname

is used, then users from the named host are trusted. That is, they may access the system with the same user name as they have on the remote system. This form may be used in both the /etc/hosts.equiv and .rhosts files.

If the line is in the form:

    hostname username

then the named user from the named host can access the system. This form may be used in individual .rhosts files to allow remote users to access the system as a different local user. If this form is used in the /etc/hosts.equiv file, the named remote user will be allowed to access the system as any local user.

Netgroups(5) can be used in either the hostname or username fields to match a number of hosts or users in one entry. The form:

    +@netgroup

allows access from all hosts in the named netgroup. When used in the username field, netgroups allow a group of remote users to access the system as a particular local user. The form:

    hostname +@netgroup

allows all of the users in the named netgroup from the named host to access the system as the local user. The form:

    +@netgroup1 +@netgroup2

allows the users in netgroup2 from the hosts in netgroup1 to access the system as the local user.

The special character `+' can be used in place of either hostname or username to match any host or user. For example, the entry

    +

will allow a user from any remote host to access the system with the same username. The entry

    + username

will allow the named user from any remote host to access the system. The entry

    hostname +

will allow any user from the named host to access the system as the local user.

  Negative Entries

Negative entries are preceded by a `-' sign. The form:

    -hostname

will disallow all access from the named host. The form:

    -@netgroup

means that access is explicitly disallowed from all hosts in the named netgroup. The form:

    hostname -username

disallows access by the named user only from the named host, while the form:

    + -@netgroup

will disallow access by all of the users in the named netgroup from all hosts.

FILES
/etc/hosts.equiv
~/.rhosts

NOTES

Hostnames in /etc/hosts.equiv and .rhosts files must be the ``official'' name of the host, not one of its nicnames.

Root access is handled as a special case. Only the /.rhosts file is checked when the access is being attempted for root. To help maintain system security, the /etc/hosts.equiv file is not checked.

As a security feature, the .rhosts file must be owned by the user as whom access is being attempted.

Positive entries in /etc/hosts.equiv that include a username field (either an individual named user, a netgroup, or `+' sign) should be used only with extreme caution. Because /etc/hosts.equiv applies system-wide, these entries allow one or a group of remote users to access the system as any local user. This can be the source of a security hole.

SEE ALSO
rlogin(1C), rsh(1C), rcp(1C), rcmd(3N), hosts(5), netgroup(5), passwd(5)