235 lines
6.8 KiB
Groff
235 lines
6.8 KiB
Groff
.\" $NetBSD: rshd.8,v 1.18 2005/03/09 16:42:49 wiz Exp $
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.\"
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.\" Copyright (c) 1983, 1989, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" from: @(#)rshd.8 8.1 (Berkeley) 6/4/93
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.\"
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.Dd March 9, 2005
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.Dt RSHD 8
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.Os
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.Sh NAME
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.Nm rshd
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.Nd remote shell server
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.Sh SYNOPSIS
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.Nm
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.Op Fl aLln
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.Sh DESCRIPTION
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The
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.Nm
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server is the server for the
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.Xr rcmd 3
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routine and, consequently, for the
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.Xr rsh 1
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program.
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The server provides remote execution facilities
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with authentication based on privileged port numbers from trusted hosts.
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.Pp
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The
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.Nm
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server listens for service requests at the port indicated in
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the
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.Dq cmd
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service specification; see
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.Xr services 5 .
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When a service request is received the following protocol
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is initiated:
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.Bl -enum
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.It
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The server checks the client's source port.
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If the port is not in the range 512-1023, the server
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aborts the connection.
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.It
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The server reads characters from the socket up
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to a null
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.Pq Sq \e0
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byte.
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The resultant string is interpreted as an
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.Tn ASCII
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number, base 10.
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.It
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If the number received in step 2 is non-zero,
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it is interpreted as the port number of a secondary
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stream to be used for the
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.Em stderr .
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A second connection is then created to the specified
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port on the client's machine.
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The source port of this
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second connection is also in the range 512-1023.
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.It
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The server checks the client's source address
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and requests the corresponding host name (see
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.Xr getnameinfo 3 ,
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.Xr hosts 5 ,
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and
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.Xr named 8 ) .
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If the hostname cannot be determined,
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the dot-notation representation of the host address is used.
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If the hostname is in the same domain as the server (according to
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the last two components of the domain name), or if the
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.Fl a
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option is given,
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the addresses for the hostname are requested,
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verifying that the name and address correspond.
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If address verification fails, the connection is aborted
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with the message
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.Dq Host address mismatch.
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.It
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A null terminated user name of at most 16 characters
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is retrieved on the initial socket.
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This user name is interpreted as the user identity on the
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.Em client Ns 's
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machine.
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.It
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A null terminated user name of at most 16 characters
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is retrieved on the initial socket.
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This user name is interpreted as a user identity to use on the
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.Sy server Ns 's
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machine.
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.It
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A null terminated command to be passed to a
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shell is retrieved on the initial socket.
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The length of the command is limited by the upper
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bound on the size of the system's argument list.
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.It
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.Nm
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then validates the user using
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.Xr ruserok 3 ,
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which uses the file
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.Pa /etc/hosts.equiv
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and the
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.Pa .rhosts
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file found in the user's home directory.
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The
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.Fl l
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option prevents
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.Xr ruserok 3
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from doing any validation based on the user's
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.Dq Pa .rhosts
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file, unless the user is the superuser.
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.It
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If the file
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.Pa /etc/nologin
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exists and the user is not the superuser,
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the connection is closed.
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.It
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A null byte is returned on the initial socket
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and the command line is passed to the normal login
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shell of the user.
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The shell inherits the network connections established by
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.Nm .
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.El
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.Pp
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Transport-level keepalive messages are enabled unless the
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.Fl n
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option is present.
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The use of keepalive messages allows sessions to be timed out
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if the client crashes or becomes unreachable.
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.Pp
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The
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.Fl L
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option causes all successful accesses to be logged to
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.Xr syslogd 8
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as
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.Li auth.info
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messages.
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.Sh DIAGNOSTICS
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Except for the last one listed below,
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all diagnostic messages
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are returned on the initial socket,
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after which any network connections are closed.
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An error is indicated by a leading byte with a value of
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1 (0 is returned in step 10 above upon successful completion
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of all the steps prior to the execution of the login shell).
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.Bl -tag -width indent
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.It Sy Locuser too long.
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The name of the user on the client's machine is
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longer than 16 characters.
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.It Sy Ruser too long.
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The name of the user on the remote machine is
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longer than 16 characters.
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.It Sy Command too long .
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The command line passed exceeds the size of the argument
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list (as configured into the system).
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.It Sy Login incorrect.
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No password file entry for the user name existed.
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.It Sy Remote directory.
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The
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.Xr chdir 2
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to the home directory failed.
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.It Sy Permission denied.
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The authentication procedure described above failed.
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.It Sy Can't make pipe.
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The pipe needed for the
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.Em stderr ,
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wasn't created.
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.It Sy Can't fork; try again.
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A
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.Xr fork 2
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by the server failed.
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.It Sy \*[Lt]shellname\*[Gt]: ...
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The user's login shell could not be started.
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This message is returned on the connection associated with the
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.Em stderr ,
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and is not preceded by a flag byte.
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.El
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.Sh SEE ALSO
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.Xr rsh 1 ,
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.Xr ssh 1 ,
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.Xr rcmd 3 ,
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.Xr ruserok 3 ,
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.Xr hosts_access 5 ,
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.Xr login.conf 5 ,
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.Xr sshd 8
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.Sh BUGS
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The authentication procedure used here assumes the integrity
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of every machine and every network that can reach the rshd/rlogind
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ports on the server.
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This is insecure, but is useful in an
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.Dq open
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environment.
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.Xr sshd 8
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or a Kerberized version of this server are much more secure.
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.Pp
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A facility to allow all data exchanges to be encrypted should be
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present.
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.Pp
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A more extensible protocol (such as Telnet) should be used.
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.Pp
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.Nm
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intentionally rejects accesses from IPv4 mapped address on top of
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.Dv AF_INET6
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socket, since IPv4 mapped address complicates
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host-address based authentication.
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If you would like to accept connections from IPv4 peers, you will
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need to run
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.Nm
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on top of an
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.Dv AF_INET
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socket, not an
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.Dv AF_INET6
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socket.
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