1.\" $NetBSD: rshd.8,v 1.13 2002/09/29 14:05:55 wiz Exp $ 2.\" 3.\" Copyright (c) 1983, 1989, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" from: @(#)rshd.8 8.1 (Berkeley) 6/4/93 35.\" 36.Dd January 22, 2000 37.Dt RSHD 8 38.Os 39.Sh NAME 40.Nm rshd 41.Nd remote shell server 42.Sh SYNOPSIS 43.Nm 44.Op Fl alnL 45.Sh DESCRIPTION 46The 47.Nm 48server is the server for the 49.Xr rcmd 3 50routine and, consequently, for the 51.Xr rsh 1 52program. 53The server provides remote execution facilities 54with authentication based on privileged port numbers from trusted hosts. 55.Pp 56The 57.Nm 58server listens for service requests at the port indicated in 59the ``cmd'' service specification; see 60.Xr services 5 . 61When a service request is received the following protocol 62is initiated: 63.Bl -enum 64.It 65The server checks the client's source port. 66If the port is not in the range 512-1023, the server 67aborts the connection. 68.It 69The server reads characters from the socket up 70to a null (`\e0') byte. 71The resultant string is interpreted as an 72.Tn ASCII 73number, base 10. 74.It 75If the number received in step 2 is non-zero, 76it is interpreted as the port number of a secondary 77stream to be used for the 78.Em stderr . 79A second connection is then created to the specified 80port on the client's machine. 81The source port of this 82second connection is also in the range 512-1023. 83.It 84The server checks the client's source address 85and requests the corresponding host name (see 86.Xr gethostbyaddr 3 , 87.Xr hosts 5 88and 89.Xr named 8 ) . 90If the hostname cannot be determined, 91the dot-notation representation of the host address is used. 92If the hostname is in the same domain as the server (according to 93the last two components of the domain name), or if the 94.Fl a 95option is given, 96the addresses for the hostname are requested, 97verifying that the name and address correspond. 98If address verification fails, the connection is aborted 99with the message, ``Host address mismatch.'' 100.It 101A null terminated user name of at most 16 characters 102is retrieved on the initial socket. 103This user name is interpreted as the user identity on the 104.Em client Ns 's 105machine. 106.It 107A null terminated user name of at most 16 characters 108is retrieved on the initial socket. 109This user name is interpreted as a user identity to use on the 110.Sy server Ns 's 111machine. 112.It 113A null terminated command to be passed to a 114shell is retrieved on the initial socket. 115The length of the command is limited by the upper 116bound on the size of the system's argument list. 117.It 118.Nm 119then validates the user using 120.Xr ruserok 3 , 121which uses the file 122.Pa /etc/hosts.equiv 123and the 124.Pa .rhosts 125file found in the user's home directory. 126The 127.Fl l 128option prevents 129.Xr ruserok 3 130from doing any validation based on the user's ``.rhosts'' file, 131unless the user is the superuser. 132.It 133If the file 134.Pa /etc/nologin 135exists and the user is not the superuser, 136the connection is closed. 137.It 138A null byte is returned on the initial socket 139and the command line is passed to the normal login 140shell of the user. 141The shell inherits the network connections established by 142.Nm "" . 143.El 144.Pp 145Transport-level keepalive messages are enabled unless the 146.Fl n 147option is present. 148The use of keepalive messages allows sessions to be timed out 149if the client crashes or becomes unreachable. 150.Pp 151The 152.Fl L 153option causes all successful accesses to be logged to 154.Xr syslogd 8 155as 156.Li auth.info 157messages. 158.Sh DIAGNOSTICS 159Except for the last one listed below, 160all diagnostic messages 161are returned on the initial socket, 162after which any network connections are closed. 163An error is indicated by a leading byte with a value of 1641 (0 is returned in step 10 above upon successful completion 165of all the steps prior to the execution of the login shell). 166.Bl -tag -width indent 167.It Sy Locuser too long. 168The name of the user on the client's machine is 169longer than 16 characters. 170.It Sy Ruser too long. 171The name of the user on the remote machine is 172longer than 16 characters. 173.It Sy Command too long . 174The command line passed exceeds the size of the argument 175list (as configured into the system). 176.It Sy Login incorrect. 177No password file entry for the user name existed. 178.It Sy Remote directory. 179The 180.Xr chdir 2 181to the home directory failed. 182.It Sy Permission denied. 183The authentication procedure described above failed. 184.It Sy Can't make pipe. 185The pipe needed for the 186.Em stderr , 187wasn't created. 188.It Sy Can't fork; try again. 189A 190.Xr fork 2 191by the server failed. 192.It Sy \*[Lt]shellname\*[Gt]: ... 193The user's login shell could not be started. 194This message is returned on the connection associated with the 195.Em stderr , 196and is not preceded by a flag byte. 197.El 198.Sh SEE ALSO 199.Xr rsh 1 , 200.Xr rcmd 3 , 201.Xr ruserok 3 , 202.Xr login.conf 5 203.Sh BUGS 204The authentication procedure used here assumes the integrity 205of each client machine and the connecting medium. 206This is insecure, but is useful in an ``open'' environment. 207.Pp 208A facility to allow all data exchanges to be encrypted should be 209present. 210.Pp 211A more extensible protocol (such as Telnet) should be used. 212.Pp 213.Nm 214intentionally rejects accesses from IPv4 mapped address on top of 215.Dv AF_INET6 216socket, since IPv4 mapped address complicates 217host-address based authentication. 218If you would like to accept connections from IPv4 peers, you will need to run 219.Nm 220on top of 221.Dv AF_INET 222socket, not 223.Dv AF_INET6 224socket. 225