1.\" Copyright (c) 1983, 1989, 1991 The Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)rshd.8 6.11 (Berkeley) 4/20/91 33.\" 34.Dd April 20, 1991 35.Dt RSHD 8 36.Os BSD 4.2 37.Sh NAME 38.Nm rshd 39.Nd remote shell server 40.Sh SYNOPSIS 41.Nm rshd 42.Op Fl aln 43.Sh DESCRIPTION 44The 45.Nm rshd 46server 47is the server for the 48.Xr rcmd 3 49routine and, consequently, for the 50.Xr rsh 1 51program. The server provides remote execution facilities 52with authentication based on privileged port numbers from trusted hosts. 53.Pp 54The 55.Nm rshd 56server 57listens for service requests at the port indicated in 58the ``cmd'' service specification; see 59.Xr services 5 . 60When a service request is received the following protocol 61is initiated: 62.Bl -enum 63.It 64The server checks the client's source port. 65If the port is not in the range 512-1023, the server 66aborts the connection. 67.It 68The server reads characters from the socket up 69to a null (`\e0') byte. The resultant string is 70interpreted as an 71.Tn ASCII 72number, base 10. 73.It 74If the number received in step 2 is non-zero, 75it is interpreted as the port number of a secondary 76stream to be used for the 77.Em stderr . 78A second connection is then created to the specified 79port on the client's machine. The source port of this 80second connection is also in the range 512-1023. 81.It 82The server checks the client's source address 83and requests the corresponding host name (see 84.Xr gethostbyaddr 3 , 85.Xr hosts 5 86and 87.Xr named 8 ) . 88If the hostname cannot be determined, 89the dot-notation representation of the host address is used. 90If the hostname is in the same domain as the server (according to 91the last two components of the domain name), 92or if the 93.Fl a 94option is given, 95the addresses for the hostname are requested, 96verifying that the name and address correspond. 97If address verification fails, the connection is aborted 98with the message, ``Host address mismatch.'' 99.It 100A null terminated user name of at most 16 characters 101is retrieved on the initial socket. This user name 102is interpreted as the user identity on the 103.Em client Ns 's 104machine. 105.It 106A null terminated user name of at most 16 characters 107is retrieved on the initial socket. This user name 108is interpreted as a user identity to use on the 109.Sy server Ns 's 110machine. 111.It 112A null terminated command to be passed to a 113shell is retrieved on the initial socket. The length of 114the command is limited by the upper bound on the size of 115the system's argument list. 116.It 117.Nm Rshd 118then validates the user using 119.Xr ruserok 3 , 120which uses the file 121.Pa /etc/hosts.equiv 122and the 123.Pa .rhosts 124file found in the user's home directory. The 125.Fl l 126option prevents 127.Xr ruserok 3 128from doing any validation based on the user's ``.rhosts'' file, 129unless the user is the superuser. 130.It 131A null byte is returned on the initial socket 132and the command line is passed to the normal login 133shell of the user. The 134shell inherits the network connections established 135by 136.Nm rshd . 137.Pp 138Transport-level keepalive messages are enabled unless the 139.Fl n 140option is present. 141The use of keepalive messages allows sessions to be timed out 142if the client crashes or becomes unreachable. 143.El 144.Sh DIAGNOSTICS 145Except for the last one listed below, 146all diagnostic messages 147are returned on the initial socket, 148after which any network connections are closed. 149An error is indicated by a leading byte with a value of 1501 (0 is returned in step 9 above upon successful completion 151of all the steps prior to the execution of the login shell). 152.Bl -tag -width indent 153.It Sy Locuser too long. 154The name of the user on the client's machine is 155longer than 16 characters. 156.It Sy Ruser too long. 157The name of the user on the remote machine is 158longer than 16 characters. 159.It Sy Command too long . 160The command line passed exceeds the size of the argument 161list (as configured into the system). 162.It Sy Login incorrect. 163No password file entry for the user name existed. 164.It Sy Remote directory. 165The 166.Xr chdir 167command to the home directory failed. 168.It Sy Permission denied. 169The authentication procedure described above failed. 170.It Sy Can't make pipe. 171The pipe needed for the 172.Em stderr , 173wasn't created. 174.It Sy Can't fork; try again. 175A 176.Xr fork 177by the server failed. 178.It Sy <shellname>: ... 179The user's login shell could not be started. This message is returned 180on the connection associated with the 181.Em stderr , 182and is not preceded by a flag byte. 183.El 184.Sh SEE ALSO 185.Xr rsh 1 , 186.Xr rcmd 3 , 187.Xr ruserok 3 188.Sh BUGS 189The authentication procedure used here assumes the integrity 190of each client machine and the connecting medium. This is 191insecure, but is useful in an ``open'' environment. 192.Pp 193A facility to allow all data exchanges to be encrypted should be 194present. 195.Pp 196A more extensible protocol (such as Telnet) should be used. 197