postfix-master/DEBUG_README.html

   1 <!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN"
   2         "http://www.w3.org/TR/html4/loose.dtd">
   3
   4 <html>
   5
   6 <head>
   7
   8 <title> Postfix Debugging Howto </title>
   9
  10 <meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
  11
  12 </head>
  13
  14 <body>
  15
  16 <h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix Debugging Howto</h1>
  17
  18 <hr>
  19
  20 <h2>Purpose of this document</h2>
  21
  22 <p> This document describes how to debug parts of the Postfix mail
  23 system when things do not work according to expectation. The methods
  24 vary from making Postfix log a lot of detail, to running some daemon
  25 processes under control of a call tracer or debugger. </p>
  26
  27 <p> The text assumes that the Postfix <a href="postconf.5.html">main.cf</a> and <a href="master.5.html">master.cf</a>
  28 configuration files are stored in directory /etc/postfix. You can
  29 use the command "<b>postconf <a href="postconf.5.html#config_directory">config_directory</a></b>" to find out the
  30 actual location of this directory on your machine. </p>
  31
  32 <p> Listed in order of increasing invasiveness, the debugging
  33 techniques are as follows: </p>
  34
  35 <ul>
  36
  37 <li><a href="#logging">Look for obvious signs of trouble</a>
  38
  39 <li><a href="#trace_mail">Debugging Postfix from inside</a>
  40
  41 <li><a href="#no_chroot">Try turning off chroot operation in
  42 master.cf</a>
  43
  44 <li><a href="#debug_peer">Verbose logging for specific SMTP
  45 connections</a>
  46
  47 <li><a href="#sniffer">Record the SMTP session with a network
  48 sniffer</a>
  49
  50 <li><a href="#verbose">Making Postfix daemon programs more verbose</a>
  51
  52 <li><a href="#man_trace">Manually tracing a Postfix daemon process</a>
  53
  54 <li><a href="#auto_trace">Automatically tracing a Postfix daemon
  55 process</a>
  56
  57 <li><a href="#ddd">Running daemon programs with the interactive
  58 ddd debugger</a>
  59
  60 <li><a href="#screen">Running daemon programs with the interactive
  61 gdb debugger</a>
  62
  63 <li><a href="#gdb">Running daemon programs under a non-interactive
  64 debugger</a>
  65
  66 <li><a href="#unreasonable">Unreasonable behavior</a>
  67
  68 <li><a href="#mail">Reporting problems to postfix-users@postfix.org</a>
  69
  70 </ul>
  71
  72 <h2><a name="logging">Look for obvious signs of trouble</a></h2>
  73
  74 <p> Postfix logs all failed and successful deliveries to a logfile.
  75 The file is usually called /var/log/maillog or /var/log/mail; the
  76 exact pathname is defined in the /etc/syslog.conf file. </p>
  77
  78 <p> When Postfix does not receive or deliver mail, the first order
  79 of business is to look for errors that prevent Postfix from working
  80 properly:  </p>
  81
  82 <blockquote>
  83 <pre>
  84 % <b>egrep '(warning|error|fatal|panic):' /some/log/file | more</b>
  85 </pre>
  86 </blockquote>
  87
  88 <p> Note: the most important message is near the BEGINNING of the
  89 output.  Error messages that come later are less useful. </p>
  90
  91 <p> The nature of each problem is indicated as follows: </p>
  92
  93 <ul>
  94
  95 <li> <p> "<b>panic</b>" indicates a problem in the software itself
  96 that only a programmer can fix. Postfix cannot proceed until this
  97 is fixed. </p>
  98
  99 <li> <p> "<b>fatal</b>" is the result of missing files, incorrect
 100 permissions, incorrect configuration file settings that you can
 101 fix.  Postfix cannot proceed until this is fixed. </p>
 102
 103 <li> <p> "<b>error</b>" reports an error condition. For safety
 104 reasons, a Postfix process will terminate when more than 13 of these
 105 happen. </p>
 106
 107 <li> <p> "<b>warning</b>" indicates a non-fatal error. These are
 108 problems that you may not be able to fix (such as a broken DNS
 109 server elsewhere on the network) but may also indicate local
 110 configuration errors that could become a problem later. </p>
 111
 112 </ul>
 113
 114 <h2><a name="trace_mail">Debugging Postfix from inside</a> </h2>
 115
 116 <p> Postfix version 2.1 and later can
 117 produce mail delivery reports for debugging purposes. These reports
 118 not only show sender/recipient addresses after address rewriting
 119 and alias expansion or forwarding, they also show information about
 120 delivery to mailbox, delivery to non-Postfix command, responses
 121 from remote SMTP servers, and so on.
 122 </p>
 123
 124 <p> Postfix can produce two types of mail delivery reports for
 125 debugging: </p>
 126
 127 <ul>
 128
 129 <li> <p> What-if: report what would happen, but do not actually
 130 deliver mail. This mode of operation is requested with: </p>
 131
 132 <pre>
 133 % <b>/usr/sbin/sendmail -bv address...</b>
 134 Mail Delivery Status Report will be mailed to &lt;your login name&gt;.
 135 </pre>
 136
 137 <li> <p> What happened: deliver mail and report successes and/or
 138 failures, including replies from remote SMTP servers.  This mode
 139 of operation is requested with: </p>
 140
 141 <pre>
 142 % <b>/usr/sbin/sendmail -v address...</b>
 143 Mail Delivery Status Report will be mailed to &lt;your login name&gt;.
 144 </pre>
 145
 146 </ul>
 147
 148 <p> These reports contain information that is generated by Postfix
 149 delivery agents. Since these run as daemon processes that cannot
 150 interact with users directly, the result is sent as mail to the
 151 sender of the test message. The format of these reports is practically
 152 identical to that of ordinary non-delivery notifications. </p>
 153
 154 <p> For a detailed example of a mail delivery status report, see
 155 the <a href="ADDRESS_REWRITING_README.html#debugging"> debugging</a>
 156 section at the end of the <a href="ADDRESS_REWRITING_README.html">ADDRESS_REWRITING_README</a> document.  </p>
 157
 158 <h2><a name="no_chroot">Try turning off chroot operation in master.cf</a></h2>
 159
 160 <p> A common mistake is to turn on chroot operation in the <a href="master.5.html">master.cf</a>
 161 file without going through all the necessary steps to set up a
 162 chroot environment. This causes Postfix daemon processes to fail
 163 due to all kinds of missing files. </p>
 164
 165 <p> The example below shows an SMTP server that is configured with
 166 chroot turned off: </p>
 167
 168 <blockquote>
 169 <pre>
 170 /etc/postfix/<a href="master.5.html">master.cf</a>:
 171     # =============================================================
 172     # service type  private unpriv  <b>chroot</b>  wakeup  maxproc command
 173     #               (yes)   (yes)   <b>(yes)</b>   (never) (100)
 174     # =============================================================
 175     smtp      inet  n       -       <b>n</b>       -       -       smtpd
 176 </pre>
 177 </blockquote>
 178
 179 <p> Inspect <a href="master.5.html">master.cf</a> for any processes that have chroot operation
 180 not turned off. If you find any, save a copy of the <a href="master.5.html">master.cf</a> file,
 181 and edit the entries in question.  After executing the command
 182 "<b>postfix reload</b>", see if the problem has gone away. </p>
 183
 184 <p> If turning off chrooted operation made the problem go away,
 185 then congratulations.  Leaving Postfix running in this way is
 186 adequate for most sites.  If you prefer chrooted operation, see
 187 the Postfix <a href="BASIC_CONFIGURATION_README.html#chroot_setup">
 188 BASIC_CONFIGURATION_README</a> file for information about how to
 189 prepare Postfix for chrooted operation. </p>
 190
 191 <h2><a name="debug_peer">Verbose logging for specific SMTP
 192 connections</a></h2>
 193
 194 <p> In /etc/postfix/<a href="postconf.5.html">main.cf</a>, list the remote site name or address
 195 in the <a href="postconf.5.html#debug_peer_list">debug_peer_list</a> parameter. For example, in order to make
 196 the software log a lot of information to the syslog daemon for
 197 connections from or to the loopback interface: </p>
 198
 199 <blockquote>
 200 <pre>
 201 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 202     <a href="postconf.5.html#debug_peer_list">debug_peer_list</a> = 127.0.0.1
 203 </pre>
 204 </blockquote>
 205
 206 <p> You can specify one or more hosts, domains, addresses or
 207 net/masks.  To make the change effective immediately, execute the
 208 command "<b>postfix reload</b>". </p>
 209
 210 <h2><a name="sniffer">Record the SMTP session with a network sniffer</a></h2>
 211
 212 <p> This example uses <b>tcpdump</b>. In order to record a conversation
 213 you need to specify a large enough buffer with the "<b>-s</b>"
 214 option or else you will miss some or all of the packet payload.
 215 </p>
 216
 217 <blockquote>
 218 <pre>
 219 # <b>tcpdump -w /file/name -s 0 host example.com and port 25</b>
 220 </pre>
 221 </blockquote>
 222
 223 <p> Older tcpdump versions don't support "<b>-s 0</b>"; in that case,
 224 use "<b>-s 2000</b>" instead.  </p>
 225
 226 <p> Run this for a while, stop with Ctrl-C when done. To view the
 227 data use a binary viewer, <b>ethereal</b>, or good old <b>less</b>.
 228 </p>
 229
 230 <h2><a name="verbose">Making Postfix daemon programs more verbose</a></h2>
 231
 232 <p> Append one or more "<b>-v</b>" options to selected daemon
 233 definitions in /etc/postfix/<a href="master.5.html">master.cf</a> and type "<b>postfix reload</b>".
 234 This will cause a lot of activity to be logged to the syslog daemon.
 235 For example, to make the Postfix SMTP server process more verbose: </p>
 236
 237 <blockquote>
 238 <pre>
 239 /etc/postfix/<a href="master.5.html">master.cf</a>:
 240     smtp      inet  n       -       n       -       -       smtpd -v
 241 </pre>
 242 </blockquote>
 243
 244 <p> To diagnose problems with address rewriting specify a "<b>-v</b>"
 245 option for the <a href="cleanup.8.html">cleanup(8)</a> and/or <a href="trivial-rewrite.8.html">trivial-rewrite(8)</a> daemon, and to
 246 diagnose problems with mail delivery specify a "<b>-v</b>"
 247 option for the <a href="qmgr.8.html">qmgr(8)</a> or <a href="qmgr.8.html">oqmgr(8)</a> queue manager, or for the <a href="lmtp.8.html">lmtp(8)</a>,
 248 <a href="local.8.html">local(8)</a>, <a href="pipe.8.html">pipe(8)</a>, <a href="smtp.8.html">smtp(8)</a>, or <a href="virtual.8.html">virtual(8)</a> delivery agent.  </p>
 249
 250 <h2><a name="man_trace">Manually tracing a Postfix daemon process</a></h2>
 251
 252 <p> Many systems allow you to inspect a running process with a
 253 system call tracer. For example: </p>
 254
 255 <blockquote>
 256 <pre>
 257 # <b>trace -p process-id</b> (SunOS 4)
 258 # <b>strace -p process-id</b> (Linux and many others)
 259 # <b>truss -p process-id</b> (Solaris, FreeBSD)
 260 # <b>ktrace -p process-id</b> (generic 4.4BSD)
 261 </pre>
 262 </blockquote>
 263
 264 <p> Even more informative are traces of system library calls.
 265 Examples: </p>
 266
 267 <blockquote>
 268 <pre>
 269 # <b>ltrace -p process-id</b> (Linux, also ported to FreeBSD and BSD/OS)
 270 # <b>sotruss -p process-id</b> (Solaris)
 271 </pre>
 272 </blockquote>
 273
 274 <p> See your system documentation for details. </p>
 275
 276 <p> Tracing a running process can give valuable information about
 277 what a process is attempting to do. This is as much information as
 278 you can get without running an interactive debugger program, as
 279 described in a later section. </p>
 280
 281 <h2><a name="auto_trace">Automatically tracing a Postfix daemon
 282 process</a></h2>
 283
 284 <p> Postfix can attach a call tracer whenever a daemon process
 285 starts.  Call tracers come in several kinds. </p>
 286
 287 <ol>
 288
 289 <li> <p> System call tracers such as <b>trace</b>, <b>truss</b>,
 290 <b>strace</b>, or <b>ktrace</b>.  These show the communication
 291 between the process and the kernel. </p>
 292
 293 <li> <p> Library call tracers such as <b>sotruss</b> and <b>ltrace</b>.
 294 These show calls of library routines, and give a better idea of
 295 what is going on within the process. </p>
 296
 297 </ol>
 298
 299 <p> Append a <b>-D</b> option to the suspect command in
 300 /etc/postfix/<a href="master.5.html">master.cf</a>, for example: </p>
 301
 302 <blockquote>
 303 <pre>
 304 /etc/postfix/<a href="master.5.html">master.cf</a>:
 305     smtp      inet  n       -       n       -       -       smtpd -D
 306 </pre>
 307 </blockquote>
 308
 309 <p> Edit the <a href="postconf.5.html#debugger_command">debugger_command</a> definition in /etc/postfix/<a href="postconf.5.html">main.cf</a>
 310 so that it invokes the call tracer of your choice, for example:
 311 </p>
 312
 313 <blockquote>
 314 <pre>
 315 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 316     <a href="postconf.5.html#debugger_command">debugger_command</a> =
 317          PATH=/bin:/usr/bin:/usr/local/bin;
 318          (truss -p $<a href="postconf.5.html#process_id">process_id</a> 2&gt&amp;1 | logger -p mail.info) &amp; sleep 5
 319 </pre>
 320 </blockquote>
 321
 322 <p> Type "<b>postfix reload</b>" and watch the logfile. </p>
 323
 324 <h2><a name="ddd">Running daemon programs with the interactive
 325 ddd debugger</a></h2>
 326
 327 <p> If you have X Windows installed on the Postfix machine, then
 328 an interactive debugger such as <b>ddd</b> can be convenient.
 329 </p>
 330
 331 <p> Edit the <a href="postconf.5.html#debugger_command">debugger_command</a> definition in /etc/postfix/<a href="postconf.5.html">main.cf</a>
 332 so that it invokes <b>ddd</b>: </p>
 333
 334 <blockquote>
 335 <pre>
 336 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 337     <a href="postconf.5.html#debugger_command">debugger_command</a> =
 338          PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin
 339          ddd $<a href="postconf.5.html#daemon_directory">daemon_directory</a>/$<a href="postconf.5.html#process_name">process_name</a> $<a href="postconf.5.html#process_id">process_id</a> &amp; sleep 5
 340 </pre>
 341 </blockquote>
 342
 343 <p> Be sure that <b>gdb</b> is in the command search path, and
 344 export <b>XAUTHORITY</b> so that X access control works, for example:
 345 </p>
 346
 347 <blockquote>
 348 <pre>
 349 % <b>setenv XAUTHORITY ~/.Xauthority</b> (csh syntax)
 350 $ <b>export XAUTHORITY=$HOME/.Xauthority</b> (sh syntax)
 351 </pre>
 352 </blockquote>
 353
 354 <p> Append a <b>-D</b> option to the suspect daemon definition in
 355 /etc/postfix/<a href="master.5.html">master.cf</a>, for example: </p>
 356
 357 <blockquote>
 358 <pre>
 359 /etc/postfix/<a href="master.5.html">master.cf</a>:
 360     smtp      inet  n       -       n       -       -       smtpd -D
 361 </pre>
 362 </blockquote>
 363
 364 <p> Stop and start the Postfix system.  This is necessary so that
 365 Postfix runs with the proper <b>XAUTHORITY</b> and <b>DISPLAY</b>
 366 settings. </p>
 367
 368 <p> Whenever the suspect daemon process is started, a debugger
 369 window pops up and you can watch in detail what happens. </p>
 370
 371 <h2><a name="screen">Running daemon programs with the interactive
 372 gdb debugger</a></h2>
 373
 374 <p> If you have the screen command installed on the Postfix machine, then
 375 you can run an interactive debugger such as <b>gdb</b> as follows. </p>
 376
 377 <p> Edit the <a href="postconf.5.html#debugger_command">debugger_command</a> definition in /etc/postfix/<a href="postconf.5.html">main.cf</a>
 378 so that it runs <b>gdb</b> inside a detached <b>screen</b> session:
 379 </p>
 380
 381 <blockquote>
 382 <pre>
 383 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 384     <a href="postconf.5.html#debugger_command">debugger_command</a> =
 385         PATH=/bin:/usr/bin:/sbin:/usr/sbin; export PATH; HOME=/root;
 386         export HOME; screen -e^tt -dmS $<a href="postconf.5.html#process_name">process_name</a> gdb
 387         $<a href="postconf.5.html#daemon_directory">daemon_directory</a>/$<a href="postconf.5.html#process_name">process_name</a> $<a href="postconf.5.html#process_id">process_id</a> &amp; sleep 2
 388 </pre>
 389 </blockquote>
 390
 391 <p> Be sure that <b>gdb</b> is in the command search path. </p>
 392
 393 <p> Append a <b>-D</b> option to the suspect daemon definition in
 394 /etc/postfix/<a href="master.5.html">master.cf</a>, for example: </p>
 395
 396 <blockquote>
 397 <pre>
 398 /etc/postfix/<a href="master.5.html">master.cf</a>:
 399     smtp      inet  n       -       n       -       -       smtpd -D
 400 </pre>
 401 </blockquote>
 402
 403 <p> Execute the command "<b>postfix reload</b>" and wait until a
 404 daemon process is started (you can see this in the maillog file).
 405 </p>
 406
 407 <p> Then attach to the screen, and debug away: </p>
 408
 409 <blockquote>
 410 <pre>
 411 # HOME=/root screen -r
 412 gdb) continue
 413 gdb) where
 414 </pre>
 415 </blockquote>
 416
 417 <h2><a name="gdb">Running daemon programs under a non-interactive
 418 debugger</a></h2>
 419
 420 <p> If you do not have X Windows installed on the Postfix machine,
 421 or if you are not familiar with interactive debuggers, then you
 422 can try to run <b>gdb</b> in non-interactive mode, and have it
 423 print a stack trace when the process crashes.  </p>
 424
 425 <p> Edit the <a href="postconf.5.html#debugger_command">debugger_command</a> definition in /etc/postfix/<a href="postconf.5.html">main.cf</a>
 426 so that it invokes the <b>gdb</b> debugger: </p>
 427
 428 <blockquote>
 429 <pre>
 430 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 431     <a href="postconf.5.html#debugger_command">debugger_command</a> =
 432         PATH=/bin:/usr/bin:/usr/local/bin; export PATH; (echo cont; echo
 433         where; sleep 8640000) | gdb $<a href="postconf.5.html#daemon_directory">daemon_directory</a>/$<a href="postconf.5.html#process_name">process_name</a>
 434         $<a href="postconf.5.html#process_id">process_id</a> 2&gt&amp;1
 435         &gt;$<a href="postconf.5.html#config_directory">config_directory</a>/$<a href="postconf.5.html#process_name">process_name</a>.$<a href="postconf.5.html#process_id">process_id</a>.log &amp; sleep 5
 436 </pre>
 437 </blockquote>
 438
 439 <p> Append a <b>-D</b> option to the suspect daemon in
 440 /etc/postfix/<a href="master.5.html">master.cf</a>, for example: </p>
 441
 442 <blockquote>
 443 <pre>
 444 /etc/postfix/<a href="master.5.html">master.cf</a>:
 445     smtp      inet  n       -       n       -       -       smtpd -D
 446 </pre>
 447 </blockquote>
 448
 449 <p> Type "<b>postfix reload</b>" to make the configuration changes
 450 effective.  </p>
 451
 452 <p> Whenever a suspect daemon process is started, an output file
 453 is created, named after the daemon and process ID (for example,
 454 smtpd.12345.log). When the process crashes, a stack trace (with
 455 output from the "<b>where</b>" command) is written to its logfile.
 456 </p>
 457
 458 <h2><a name="unreasonable">Unreasonable behavior</a></h2>
 459
 460 <p> Sometimes the behavior exhibited by Postfix just does not match the
 461 source code. Why can a program deviate from the instructions given
 462 by its author? There are two possibilities. </p>
 463
 464 <ul>
 465
 466 <li> <p> The compiler has erred. This rarely happens. </p>
 467
 468 <li> <p> The hardware has erred. Does the machine have ECC memory? </p>
 469
 470 </ul>
 471
 472 <p> In both cases, the program being executed is not the program
 473 that was supposed to be executed, so anything could happen. </p>
 474
 475 <p> There is a third possibility: </p>
 476
 477 <ul>
 478
 479 <li> <p> Bugs in system software (kernel or libraries). </p>
 480
 481 </ul>
 482
 483 <p> Hardware-related failures usually do not reproduce in exactly
 484 the same way after power cycling and rebooting the system.  There's
 485 little Postfix can do about bad hardware.  Be sure to use hardware
 486 that at the very least can detect memory errors.  Otherwise, Postfix
 487 will just be waiting to be hit by a bit error.  Critical systems
 488 deserve real hardware. </p>
 489
 490 <p> When a compiler makes an error, the problem can be reproduced
 491 whenever the resulting program is run. Compiler errors are most
 492 likely to happen in the code optimizer. If a problem is reproducible
 493 across power cycles and system reboots, it can be worthwhile to
 494 rebuild Postfix with optimization disabled, and to see if optimization
 495 makes a difference. </p>
 496
 497 <p> In order to compile Postfix with optimizations turned off: </p>
 498
 499 <blockquote>
 500 <pre>
 501 % <b>make tidy</b>
 502 % <b>make makefiles OPT=</b>
 503 </pre>
 504 </blockquote>
 505
 506 <p> This produces a set of Makefiles that do not request compiler
 507 optimization.  </p>
 508
 509 <p> Once the makefiles are set up, build the software: </p>
 510
 511 <blockquote>
 512 <pre>
 513 % <b>make</b>
 514 % <b>su</b>
 515 Password:
 516 # <b>make install</b>
 517 </pre>
 518 </blockquote>
 519
 520 <p> If the problem goes away, then it is time to ask your vendor
 521 for help. </p>
 522
 523 <h2><a name="mail">Reporting problems to postfix-users@postfix.org</a></h2>
 524
 525 <p> The people who participate on postfix-users@postfix.org
 526 are very helpful, especially if YOU provide them with sufficient
 527 information.  Remember, these volunteers are willing to help, but
 528 their time is limited. </p>
 529
 530 <p> When reporting a problem, be sure to include the following
 531 information. </p>
 532
 533 <ul>
 534
 535 <li> <p> A summary of the problem. Please do not just send some
 536 logging without explanation of what YOU believe is wrong. </p>
 537
 538 <li> <p> Complete error messages. Please use cut-and-paste, or use
 539 attachments, instead of reciting information from memory.
 540 </p>
 541
 542 <li> <p> Postfix logging. See the text at the top of the <a href="DEBUG_README.html">DEBUG_README</a>
 543 document to find out where logging is stored. Please do not frustrate
 544 the helpers by word wrapping the logging. If the logging is more
 545 than a few kbytes of text, consider posting an URL on a web or ftp
 546 site. </p>
 547
 548 <li> <p> Consider using a test email address so that you don't have
 549 to reveal email addresses or passwords of innocent people. </p>
 550
 551 <li> <p> If you can't use a test email address, please anonymize
 552 email addresses and host names consistently. Replace each letter
 553 by "A", each digit
 554 by "D" so that the helpers can still recognize syntactical errors.
 555 </p>
 556
 557 <li> <p> Output from "<b>postconf -n</b>". Please do not send your
 558 <a href="postconf.5.html">main.cf</a> file, or 500+ lines of <b>postconf</b> output. </p>
 559
 560 <li> <p> Better, provide output from the <b>postfinger</b> tool.
 561 This can be found at <a href="http://ftp.wl0.org/SOURCES/postfinger">http://ftp.wl0.org/SOURCES/postfinger</a>.  </p>
 562
 563 <li> <p> If the problem is SASL related, consider including the
 564 output from the <b>saslfinger</b> tool. This can be found at
 565 <a href="http://postfix.state-of-mind.de/patrick.koetter/saslfinger/">http://postfix.state-of-mind.de/patrick.koetter/saslfinger/</a>. </p>
 566
 567 <li> <p> If the problem is about too much mail in the queue, consider
 568 including output from the <b>qshape</b> tool, as described in the
 569 <a href="QSHAPE_README.html">QSHAPE_README</a> file. </p>
 570
 571 <li> <p> If the problem is protocol related (connections time out,
 572 or an SMTP server complains about syntax errors etc.) consider
 573 recording a session with <b>tcpdump</b>, as described in the <a
 574 href="#sniffer">DEBUG_README</a> document.  </ul>
 575
 576 </body>
 577
 578 </html>