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34 .TH TFTPD 8 "23 October 2002" "tftp-hpa @@VERSION@@" "System Manager's Manual"
35 .SH NAME
36 .B tftpd
37 \- IPv4 Trivial File Transfer Protocol server
38 .SH SYNOPSIS
39 .B in.tftpd
40 .RI [ options... ]
41 .I directory...
42 .SH DESCRIPTION
43 .B tftpd
44 is a server for the IPv4 Trivial File Transfer Protocol. The TFTP
45 protocol is extensively used to support remote booting of diskless
46 devices. The server is normally started by
47 .BR inetd ,
48 but can also run standalone.
49 .PP
50 .SH OPTIONS
51 .TP
52 .B \-l
53 Run the server in standalone (listen) mode, rather than run from
54 .BR inetd .
55 In listen mode, the
56 .B \-t
57 option is ignored, and the
58 .B \-a
59 option can be used to specify a specific local address or port to
60 listen to.
61 .TP
62 \fB\-a\fP \fI[address][:port]\fP
63 Specify a specific
64 .I address
65 and
66 .I port
67 to listen to when called with the
68 .B \-l
69 option. The default is to listen to the
70 .I tftp
71 port specified in
72 .I /etc/services
73 on all local addresses.
74 .TP
75 .B \-c
76 Allow new files to be created. By default,
77 .B tftpd
78 will only allow upload of files that already exist. Files are created
79 with default permissions allowing anyone to read or write them, unless
80 the
81 .B \-p
82 or
83 .B \-U
84 options are specified.
85 .TP
86 .B \-s
87 Change root directory on startup. This means the remote host does not
88 need to pass along the directory as part of the transfer, and may add
89 security. When
90 .B \-s
91 is specified, exactly one
92 .I directory
93 should be specified on the command line. The use of this option is
94 recommended for security as well as compatibility with some boot ROMs
95 which cannot be easily made to include a directory name in its request.
96 .TP
97 \fB\-u\fP \fIusername\fP
98 Specify the username which
99 .B tftpd
100 will run as; the default is "nobody". The user ID, group ID, and (if
101 possible on the platform) the supplementary group IDs will be set to
102 the ones specified in the system permission database for this
103 username.
104 .TP
105 \fB\-U\fP \fIumask\fP
106 Sets the \fIumask\fP for newly created files to the specified value.
107 The default is zero (anyone can read or write) if the
108 .B \-p
109 option is not specified, or inherited from the invoking process if
110 .B \-p
111 is specified.
112 .TP
113 .B \-p
114 Perform no additional permissions checks above the normal
115 system-provided access controls for the user specified via the
116 .B \-u
117 option.
118 .TP
119 \fB\-t\fP \fItimeout\fP
120 When run from
121 .B inetd
122 this specifies how long, in seconds, to wait for a second connection
123 before terminating the server.
124 .B inetd
125 will then respawn the server when another request comes in. The
126 default is 900 (15 minutes.)
127 .TP
128 \fB\-T\fP \fItimeout\fP
129 Determine the default timeout, in microseconds, before the first
130 packet is retransmitted. This can be modified by the client if the
131 .B timeout
132 or
133 .B utimeout
134 option is negotiated. The default is 1000000 (1 second.)
135 .TP
136 \fB\-m\fP \fIremap-file\fP
137 Specify the use of filename remapping. The
138 .I remap-file
139 is a file containing the remapping rules. See the section on filename
140 remapping below. This option may not be compiled in, see the output of
141 .B "in.tftpd \-V"
142 to verify whether or not it is available.
143 .TP
144 .B \-v
145 Increase the logging verbosity of
146 .BR tftpd .
147 This flag can be specified multiple times for even higher verbosity.
148 .TP
149 \fB\-r\fP \fItftp-option\fP
150 Indicate that a specific RFC 2347 TFTP option should never be
151 accepted.
152 .TP
153 .B \-V
154 Print the version number and configuration to standard output, then
155 exit gracefully.
156 .SH "RFC 2347 OPTION NEGOTIATION"
157 This version of
158 .B tftpd
159 supports RFC 2347 option negotation. Currently implemented options
160 are:
161 .TP
162 \fBblksize\fP (RFC 2348)
163 Set the transfer block size to anything less than or equal to the
164 specified option. This version of
165 .B tftpd
166 can support any block size up to the theoretical maximum of 65464
167 bytes.
168 .TP
169 \fBblksize2\fP (nonstandard)
170 Set the transfer block size to anything less than or equal to the
171 specified option, but restrict the possible responses to powers of 2.
172 The maximum is 32768 bytes (the largest power of 2 less than or equal
173 to 65464.)
174 .TP
175 \fBtsize\fP (RFC 2349)
176 Report the size of the file that is about to be transferred. This
177 version of
178 .B tftpd
179 only supports the
180 .B tsize
181 option for binary (octet) mode transfers.
182 .TP
183 \fBtimeout\fP (RFC 2349)
184 Set the time before the server retransmits a packet, in seconds.
185 .TP
186 \fButimeout\fP (nonstandard)
187 Set the time before the server retransmits a packet, in microseconds.
188 and
189 .PP
190 The
191 .B \-r
192 option can be used to disable specific options; this may be necessary
193 to work around bugs in specific TFTP client implementations. For
194 example, some TFTP clients have been found to request the
195 .B blksize
196 option, but crash with an error if they actually get the option
197 accepted by the server.
198 .SH "FILENAME REMAPPING"
199 The
200 .B \-m
201 option specifies a file which contains filename remapping rules. Each
202 non-comment line (comments begin with hash marks,
203 .BR # )
204 contains an
205 .IR operation ,
206 specified below; a
207 .IR regex ,
208 a regular expression in the style of
209 .BR egrep ;
210 and optionally a
211 .IR "replacement pattern" .
212 The operation indicated by
213 .I operation
214 is performed if the
215 .I regex
216 matches all or part of the filename. Rules are processed from the top
217 down, and by default, all rules are processed even if there is a
218 match.
219 .PP
220 The
221 .I operation
222 can be any combination of the following letters:
223 .TP
224 .B r
225 Replace the substring matched by
226 .I regex
227 by the
228 .IR "replacement pattern" .
229 The replacement pattern may contain escape sequences; see below.
230 .TP
231 .B g
232 Repeat this rule until it no longer matches. This is always used with
233 .BR r .
234 .TP
235 .B i
236 Match the
237 .I regex
238 case-insensitively. By default it is case sensitive.
239 .TP
240 .B e
241 If this rule matches, end rule processing after executing the rule.
242 .TP
243 .B s
244 If this rule matches, start rule processing over from the very first
245 rule after executing this rule.
246 .TP
247 .B a
248 If this rule matches, refuse the request and send an access denied
249 error to the client.
250 .TP
251 .B G
252 This rule applies to GET (RRQ) requests only.
253 .TP
254 .B P
255 This rule applies to PUT (WRQ) requests only.
256 .PP
257 The following escape sequences are recognized as part of the
258 .IR "replacement pattern" :
259 .TP
260 \fB\\0\fP
261 The entire string matched by the
262 .IR regex .
263 .TP
264 \fB\\1\fP to \fB\\9\fP
265 The strings matched by each of the first nine parenthesized
266 subexpressions, \\( ... \\), of the
267 .I regex
268 pattern.
269 .TP
270 \fB\\i\fP
271 The IP address of the requesting host, in dotted-quad notation
272 (e.g. 192.0.2.169).
273 .TP
274 \fB\\x\fP
275 The IP address of the requesting host, in hexadecimal notation
276 (e.g. C00002A9).
277 .TP
278 \fB\\\\\fP
279 Literal backslash.
280 .TP
281 \fB\\\fP\fIwhitespace\fP
282 Literal whitespace.
283 .TP
284 \fB\\#\fI
285 Literal hash mark.
286 .PP
287 If the mapping file is changed, you need to send
288 .B SIGHUP
289 to any outstanding
290 .B tftpd
291 process.
292 .SH "SECURITY"
293 The use of TFTP services does not require an account or password on
294 the server system. Due to the lack of authentication information,
295 .B tftpd
296 will allow only publicly readable files (o+r) to be accessed, unless the
297 .B \-p
298 option is specified. Files may be written only if they already exist
299 and are publicly writable, unless the
300 .B \-c
301 option is specified. Note that this extends the concept of ``public''
302 to include all users on all hosts that can be reached through the
303 network; this may not be appropriate on all systems, and its
304 implications should be considered before enabling TFTP service.
305 Typically, some kind of firewall or packet-filter solution should be
306 employed. If appropriately compiled (see the output of
307 .BR "in.tftpd \-V" )
308 .B tftpd
309 will query the
310 .BR hosts_access (5)
311 database for access control information. This may be slow; sites
312 requiring maximum performance may want to compile without this option
313 and rely on firewalling or kernel-based packet filters instead.
314 .PP
315 The server should be set to run as the user with the lowest possible
316 privilege; please see the
317 .B \-u
318 flag. It is probably a good idea to set up a specific user account for
319 .BR tftpd ,
320 rather than letting it run as "nobody", to guard against privilege
321 leaks between applications.
322 .PP
323 Access to files can, and should, be restricted by invoking
324 .B tftpd
325 with a list of directories by including pathnames as server program
326 arguments on the command line. In this case access is restricted to
327 files whole names are prefixed by one of the given directories. If
328 possible, it is recommended that the
329 .B \-s
330 flag is used to set up a chroot() environment for the server to run in
331 once a connection has been set up.
332 .PP
333 Finally, the filename remapping
334 .RB ( \-m
335 flag) support can be used to provide a limited amount of additional
336 access control.
337 .SH "CONFORMING TO"
338 RFC 1123,
339 .IR "Requirements for Internet Hosts \- Application and Support" .
340 .br
341 RFC 1350,
342 .IR "The TFTP Protocol (revision 2)" .
343 .br
344 RFC 2347,
345 .IR "TFTP Option Extension" .
346 .br
347 RFC 2348,
348 .IR "TFTP Blocksize Option" .
349 .br
350 RFC 2349,
351 .IR "TFTP Timeout Interval and Transfer Size Options" .
352 .SH "AUTHOR"
353 This version of
354 .B tftpd
355 is maintained by H. Peter Anvin <hpa@zytor.com>. It was derived from,
356 but has substantially diverged from, an OpenBSD source base, with
357 added patches by Markus Gutschke and Gero Kulhman.
358 .SH "SEE ALSO"
359 .BR tftp (1),
360 .BR egrep (1),
361 .BR umask (2),
362 .BR hosts_access (5),
363 .BR regex (7),
364 .BR inetd (8).