RHOSTS(5) File Formats Manual RHOSTS(5)NAME
rhosts, hosts.equiv - trusted remote users or hosts
SYNOPSIS
~user/.rhosts
/etc/hosts.equiv
DESCRIPTION
The per user .rhosts and the per system hosts.equiv files can be used to allow users to use rlogin or rsh without a password. The remote
login services first check the system wide /etc/hosts.equiv file and then the ~user/.rhosts of the intended user. Both files contain lines
of one of two forms:
host
host ruser
The first form tells that any user from host is allowed to login to this system under the same name. The second form allows ruser from
host to login.
The .rhosts file is checked to be owned by user or root, and only its owner may be able to write it.
SEE ALSO rlogin(1), rsh(1).
NOTES
Minix has no restrictions on becoming super-user remotely. Other systems usually do.
AUTHOR
Kees J. Bot (kjb@cs.vu.nl)
RHOSTS(5)
Check Out this Related Man Page
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 supplying
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 consisting
of the entries
+
-hostxxx
will not deny access to "hostxxx".
SunOS 5.11 23 Jun 1997 hosts.equiv(4)