hosts.equiv(5) [osx man page]
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 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'' neg- ative entries. BSD
November 26, 1997 BSD
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hosts.equiv(4) File Formats hosts.equiv(4) NAME
hosts.equiv, rhosts - trusted remote hosts and users DESCRIPTION
The /etc/hosts.equiv and .rhosts files provide the "remote authentication" database for rlogin(1), rsh(1), rcp(1), and rcmd(3SOCKET). The files specify remote hosts and users that are considered "trusted". Trusted users are allowed to access the local system without supply- ing a password. The library routine ruserok() (see rcmd(3SOCKET)) 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 user from a remote host should be allowed to access the local system with the identity of a 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 who is requesting access. Entries in these files can be of two forms. Positive entries allow access, while negative entries deny access. The authentication succeeds when a matching positive entry is found. The procedure fails when the first matching nega- tive entry is found, or if no matching entries are found in either file. The order of entries is important. If the files contain both posi- tive and negative entries, the entry that appears first will prevail. The rsh(1) and rcp(1) programs fail if the remote authentication pro- cedure fails. The rlogin program falls 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] Hostnames must be the official name of the host, not one of its nicknames. 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. netgroup(4) 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. Search Sequence To help maintain system security, the /etc/hosts.equiv file is not checked when access is being attempted for super-user. If the user attempting access is not the super-user, /etc/hosts.equiv is searched for lines of the form described above. Checks are made for lines in this file in the following order: 1. + 2. +@netgroup 3. -@netgroup 4. -hostname 5. hostname The user is granted access if a positive match occurrs. Negative entries apply only to /etc/hosts.equiv and may be overridden by subse- quent .rhosts entries. If no positive match occurred, the .rhosts file is then searched if the user attempting access maintains such a file. This file is searched whether or not the user attempting access is the super-user. As a security feature, the .rhosts file must be owned by the user who is attempting access. Checks are made for lines in .rhosts in the following order: 1. + 2. +@netgroup 3. -@netgroup 4. -hostname 5. hostname FILES
/etc/hosts.equiv system trusted hosts and users ~/.rhosts user's trusted hosts and users SEE ALSO
rcp(1), rlogin(1), rsh(1), rcmd(3SOCKET), hosts(4), netgroup(4), passwd(4) WARNINGS
Positive entries in /etc/hosts.equiv that include a username field (either an individual named user, a netgroup, or `+' sign) should be used 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 a security hole. For example, because of the search sequence, an /etc/hosts.equiv file consist- ing of the entries + -hostxxx will not deny access to "hostxxx". SunOS 5.10 23 Jun 1997 hosts.equiv(4)