.\" Copyright (c) 1983, 1989, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 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 .\" SUCH DAMAGE. .\" .\" @(#)rshd.8 8.1 (Berkeley) 6/4/93 .\" .Dd June 4, 1993 .Dt RSHD 8 .Os BSD 4.2 .Sh NAME .Nm rshd .Nd remote shell server .Sh SYNOPSIS .Nm rshd .Op Fl alnL .Sh DESCRIPTION The .Nm rshd server is the server for the .Xr rcmd 3 routine and, consequently, for the .Xr rsh 1 program. The server provides remote execution facilities with authentication based on privileged port numbers from trusted hosts. .Pp The .Nm rshd server listens for service requests at the port indicated in the ``cmd'' service specification; see .Xr services 5 . When a service request is received the following protocol is initiated: .Bl -enum .It The server checks the client's source port. If the port is not in the range 512-1023, the server aborts the connection. .It The server reads characters from the socket up to a null (`\e0') byte. The resultant string is interpreted as an .Tn ASCII number, base 10. .It 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 .Em stderr . 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. .It The server checks the client's source address and requests the corresponding host name (see .Xr gethostbyaddr 3 , .Xr hosts 5 and .Xr named 8 ) . 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), or if the .Fl a option is given, 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.'' .It 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 .Em client Ns 's machine. .It 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 .Sy server Ns 's machine. .It 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. .It .Nm Rshd then validates the user using .Xr ruserok 3 , which uses the file .Pa /etc/hosts.equiv and the .Pa .rhosts file found in the user's home directory. The .Fl l option prevents .Xr ruserok 3 from doing any validation based on the user's ``.rhosts'' file, unless the user is the superuser. .It If the file .Pa /etc/nologin exists and the user is not the superuser, the connection is closed. .It A null byte is returned on the initial socket and the command line is passed to the normal login shell of the user. The shell inherits the network connections established by .Nm rshd . .El .Pp Transport-level keepalive messages are enabled unless the .Fl n option is present. The use of keepalive messages allows sessions to be timed out if the client crashes or becomes unreachable. .Pp The .Fl L option causes all successful accesses to be logged to .Xr syslogd 8 as .Li auth.info messages. .Sh DIAGNOSTICS Except for the last one listed below, all diagnostic messages 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 10 above upon successful completion of all the steps prior to the execution of the login shell). .Bl -tag -width indent .It Sy Locuser too long. The name of the user on the client's machine is longer than 16 characters. .It Sy Ruser too long. 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). .It Sy Login incorrect. No password file entry for the user name existed. .It Sy Remote directory. The .Xr chdir command to the home directory failed. .It Sy Permission denied. The authentication procedure described above failed. .It Sy Can't make pipe. The pipe needed for the .Em stderr , wasn't created. .It Sy Can't fork; try again. A .Xr fork by the server failed. .It Sy <shellname>: ... The user's login shell could not be started. This message is returned on the connection associated with the .Em stderr , and is not preceded by a flag byte. .El .Sh SEE ALSO .Xr rsh 1 , .Xr rcmd 3 , .Xr ruserok 3 .Sh BUGS 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. .Pp A facility to allow all data exchanges to be encrypted should be present. .Pp A more extensible protocol (such as Telnet) should be used.