.\" Copyright (c) 1983, 1989, 1991 The Regents of the University of California.
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" @(#)rshd.8 6.11 (Berkeley) 4/20/91
routine and, consequently, for the
program. The server provides remote execution facilities
with authentication based on privileged port numbers from trusted hosts.
listens for service requests at the port indicated in
the ``cmd'' service specification; see
When a service request is received the following protocol
The server checks the client's source port.
If the port is not in the range 512-1023, the server
The server reads characters from the socket up
to a null (`\e0') byte. The resultant string is
If the number received in step 2 is non-zero,
it is interpreted as the port number of a secondary
stream to be used for the
A second connection is then created to the specified
port on the client's machine. The source port of this
second connection is also in the range 512-1023.
The server checks the client's source address
and requests the corresponding host name (see
If the hostname cannot be determined,
the dot-notation representation of the host address is used.
If the hostname is in the same domain as the server (according to
the last two components of the domain name),
the addresses for the hostname are requested,
verifying that the name and address correspond.
If address verification fails, the connection is aborted
with the message, ``Host address mismatch.''
A null terminated user name of at most 16 characters
is retrieved on the initial socket. This user name
is interpreted as the user identity on the
A null terminated user name of at most 16 characters
is retrieved on the initial socket. This user name
is interpreted as a user identity to use on the
A null terminated command to be passed to a
shell is retrieved on the initial socket. The length of
the command is limited by the upper bound on the size of
the system's argument list.
then validates the user using
file found in the user's home directory. The
from doing any validation based on the user's ``.rhosts'' file,
unless the user is the superuser.
A null byte is returned on the initial socket
and the command line is passed to the normal login
shell inherits the network connections established
Transport-level keepalive messages are enabled unless the
The use of keepalive messages allows sessions to be timed out
if the client crashes or becomes unreachable.
Except for the last one listed below,
are returned on the initial socket,
after which any network connections are closed.
An error is indicated by a leading byte with a value of
1 (0 is returned in step 9 above upon successful completion
of all the steps prior to the execution of the login shell).
The name of the user on the client's machine is
longer than 16 characters.
The name of the user on the remote machine is
longer than 16 characters.
.It Sy Command too long .
The command line passed exceeds the size of the argument
list (as configured into the system).
No password file entry for the user name existed.
command to the home directory failed.
.It Sy Permission denied.
The authentication procedure described above failed.
.It Sy Can't fork; try again.
The user's login shell could not be started. This message is returned
on the connection associated with the
and is not preceded by a flag byte.
The authentication procedure used here assumes the integrity
of each client machine and the connecting medium. This is
insecure, but is useful in an ``open'' environment.
A facility to allow all data exchanges to be encrypted should be
A more extensible protocol (such as Telnet) should be used.