253 lines
6.5 KiB
Groff
253 lines
6.5 KiB
Groff
.\" $NetBSD: tftpd.8,v 1.31 2019/01/09 17:19:08 uwe Exp $
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.\"
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.\" Copyright (c) 1983, 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: @(#)tftpd.8 8.1 (Berkeley) 6/4/93
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.\"
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.Dd May 5, 2015
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.Dt TFTPD 8
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.Os
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.Sh NAME
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.Nm tftpd
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.Nd
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.Tn DARPA
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Internet Trivial File Transfer Protocol server
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.Sh SYNOPSIS
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.Nm
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.Op Fl bcdln
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.Op Fl g Ar group
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.Op Fl p Ar pathsep
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.Op Fl s Ar directory
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.Op Fl u Ar user
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.Op Ar directory ...
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.Sh DESCRIPTION
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.Nm
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is a server which supports the
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.Tn DARPA
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Trivial File Transfer Protocol.
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The
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.Tn TFTP
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server operates at the port indicated in the
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.Ql tftp
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service description; see
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.Xr services 5 .
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The server is normally started by
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.Xr inetd 8 .
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.Pp
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The use of
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.Xr tftp 1
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does not require an account or password on the remote system.
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Due to the lack of authentication information,
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.Nm
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will allow only publicly readable files to be accessed.
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Filenames beginning in
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.Dq Pa ../
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or containing
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.Dq Pa /../
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are not allowed.
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Unless
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.Fl c
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is used,
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files may be written to only if they already exist and are publicly writable.
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.Pp
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Note that this extends the concept of
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.Qq public
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to include
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all users on all hosts that can be reached through the network;
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this may not be appropriate on all systems, and its implications
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should be considered before enabling tftp service.
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The server should have the user ID with the lowest possible privilege.
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.Pp
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Access to files may be restricted by invoking
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.Nm
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with a list of directories by including up to 20 pathnames
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as server program arguments in
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.Pa /etc/inetd.conf .
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In this case access is restricted to files whose
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names are prefixed by the one of the given directories.
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The given directories are also treated as a search path for
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relative filename requests.
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.Pp
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The options are:
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.Bl -tag -width "XsXdirectoryX"
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.It Fl b
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Allow clients which return acknowledgements to the broadcast address to
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communicate with the tftp server.
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Some tftp clients, notably ones resident in the ROMs of older Cisco
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equipment, return their acknowledgements to the broadcast address rather
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than the server's unicast address.
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.It Fl c
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Allow unrestricted creation of new files.
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Without this flag, only existing publicly writable files can be overwritten.
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.It Fl d
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Enable verbose debugging messages to
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.Xr syslogd 8 .
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.It Fl g Ar group
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Change gid to that of
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.Ar group
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on startup.
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If this isn't specified, the gid is set to that of the
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.Ar user
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specified with
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.Fl u .
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.It Fl l
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Logs all requests using
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.Xr syslog 3 .
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.It Fl n
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Suppresses negative acknowledgement of requests for nonexistent
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relative filenames.
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.It Fl p Ar pathsep
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All occurrences of the single character
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.Ar pathsep
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(path separator) in the requested filename are replaced with
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.Sq / .
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.It Fl s Ar directory
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.Nm
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will
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.Xr chroot 2
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to
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.Ar directory
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on startup.
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This is recommended for security reasons (so that files other than
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those in the
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.Pa /tftpboot
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directory aren't accessible).
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If the remote host passes the directory name as part of the
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file name to transfer, you may have to create a symbolic link
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from
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.Sq tftpboot
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to
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.Sq \&.
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under
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.Pa /tftpboot .
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.It Fl u Ar user
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Change uid to that of
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.Ar user
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on startup.
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If
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.Fl u
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isn't given,
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.Ar user
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defaults to
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.Dq nobody .
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If
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.Fl g
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isn't also given, change the gid to that of
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.Ar user
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as well.
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.El
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.Sh SEE ALSO
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.Xr tftp 1 ,
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.Xr inetd 8
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.Rs
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.%R RFC
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.%N 1350
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.%D July 1992
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.%T "The TFTP Protocol (Revision 2)"
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.Re
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.Rs
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.%R RFC
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.%N 2347
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.%D May 1998
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.%T "TFTP Option Extension"
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.Re
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.Rs
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.%R RFC
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.%N 2348
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.%D May 1998
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.%T "TFTP Blocksize Option"
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.Re
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.Rs
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.%R RFC
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.%N 2349
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.%D May 1998
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.%T "TFTP Timeout Interval and Transfer Size Options"
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.Re
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.Sh HISTORY
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The
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.Nm
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command appeared in
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.Bx 4.2 .
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.Pp
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The
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.Fl s
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flag appeared in
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.Nx 1.0 .
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.Pp
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The
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.Fl g
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and
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.Fl u
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flags appeared in
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.Nx 1.4 .
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.Pp
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IPv6 support was implemented by WIDE/KAME project in 1999.
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.Pp
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TFTP options were implemented by Wasabi Systems, Inc., in 2003,
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and first appeared in
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.Nx 2.0 .
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.Sh BUGS
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Files larger than 33,553,919 octets (65535 blocks, last one less than 512
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octets) cannot be correctly transferred without client and server
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supporting blocksize negotiation (RFCs 2347 and 2348).
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As a kludge,
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.Nm
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accepts a sequence of block numbers which wrap to zero after 65535.
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.Pp
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Many tftp clients will not transfer files over 16,776,703 octets
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(32767 blocks), as they incorrectly count the block number using
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a signed rather than unsigned 16-bit integer.
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.Sh SECURITY CONSIDERATIONS
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You are
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.Em strongly
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advised to set up
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.Nm
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using the
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.Fl s
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flag in conjunction with the name of the directory that
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contains the files that
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.Nm
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will serve to remote hosts (e.g.,
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.Pa /tftpboot ) .
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This ensures that only the files that should be served
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to remote hosts can be accessed by them.
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.Pp
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Because there is no user-login or validation within
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the
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.Tn TFTP
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protocol, the remote site will probably have some
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sort of file-access restrictions in place.
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The exact methods are specific to each site and therefore
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difficult to document here.
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.Pp
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If unrestricted file upload is enabled via the
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.Fl c
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option, care should be taken that this can be used
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to fill up disk space in an uncontrolled manner
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if this is used in an insecure environment.
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