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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 12:06:34 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 12:06:34 +0000
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parentInitial commit. (diff)
downloadpostfix-upstream/3.5.24.tar.xz
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Adding upstream version 3.5.24.upstream/3.5.24upstream
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+<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN"
+ "http://www.w3.org/TR/html4/loose.dtd">
+
+<html>
+
+<head>
+
+<title> Postfix Debugging Howto </title>
+
+<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
+
+</head>
+
+<body>
+
+<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix Debugging Howto</h1>
+
+<hr>
+
+<h2>Purpose of this document</h2>
+
+<p> This document describes how to debug parts of the Postfix mail
+system when things do not work according to expectation. The methods
+vary from making Postfix log a lot of detail, to running some daemon
+processes under control of a call tracer or debugger. </p>
+
+<p> The text assumes that the Postfix main.cf and master.cf
+configuration files are stored in directory /etc/postfix. You can
+use the command "<b>postconf config_directory</b>" to find out the
+actual location of this directory on your machine. </p>
+
+<p> Listed in order of increasing invasiveness, the debugging
+techniques are as follows: </p>
+
+<ul>
+
+<li><a href="#logging">Look for obvious signs of trouble</a>
+
+<li><a href="#trace_mail">Debugging Postfix from inside</a>
+
+<li><a href="#no_chroot">Try turning off chroot operation in
+master.cf</a>
+
+<li><a href="#debug_peer">Verbose logging for specific SMTP
+connections</a>
+
+<li><a href="#sniffer">Record the SMTP session with a network
+sniffer</a>
+
+<li><a href="#verbose">Making Postfix daemon programs more verbose</a>
+
+<li><a href="#man_trace">Manually tracing a Postfix daemon process</a>
+
+<li><a href="#auto_trace">Automatically tracing a Postfix daemon
+process</a>
+
+<li><a href="#ddd">Running daemon programs with the interactive
+ddd debugger</a>
+
+<li><a href="#screen">Running daemon programs with the interactive
+gdb debugger</a>
+
+<li><a href="#gdb">Running daemon programs under a non-interactive
+debugger</a>
+
+<li><a href="#unreasonable">Unreasonable behavior</a>
+
+<li><a href="#mail">Reporting problems to postfix-users@postfix.org</a>
+
+</ul>
+
+<h2><a name="logging">Look for obvious signs of trouble</a></h2>
+
+<p> Postfix logs all failed and successful deliveries to a logfile. </p>
+
+<ul>
+
+<li> <p> When Postfix uses syslog logging (the default), the file
+is usually called /var/log/maillog, /var/log/mail, or something
+similar; the exact pathname is configured in a file called
+/etc/syslog.conf, /etc/rsyslog.conf, or something similar. </p>
+
+<li> <p> When Postfix uses its own logging system (see MAILLOG_README),
+the location of the logfile is configured with the Postfix maillog_file
+parameter. </p>
+
+</ul>
+
+<p> When Postfix does not receive or deliver mail, the first order
+of business is to look for errors that prevent Postfix from working
+properly: </p>
+
+<blockquote>
+<pre>
+% <b>egrep '(warning|error|fatal|panic):' /some/log/file | more</b>
+</pre>
+</blockquote>
+
+<p> Note: the most important message is near the BEGINNING of the
+output. Error messages that come later are less useful. </p>
+
+<p> The nature of each problem is indicated as follows: </p>
+
+<ul>
+
+<li> <p> "<b>panic</b>" indicates a problem in the software itself
+that only a programmer can fix. Postfix cannot proceed until this
+is fixed. </p>
+
+<li> <p> "<b>fatal</b>" is the result of missing files, incorrect
+permissions, incorrect configuration file settings that you can
+fix. Postfix cannot proceed until this is fixed. </p>
+
+<li> <p> "<b>error</b>" reports an error condition. For safety
+reasons, a Postfix process will terminate when more than 13 of these
+happen. </p>
+
+<li> <p> "<b>warning</b>" indicates a non-fatal error. These are
+problems that you may not be able to fix (such as a broken DNS
+server elsewhere on the network) but may also indicate local
+configuration errors that could become a problem later. </p>
+
+</ul>
+
+<h2><a name="trace_mail">Debugging Postfix from inside</a> </h2>
+
+<p> Postfix version 2.1 and later can
+produce mail delivery reports for debugging purposes. These reports
+not only show sender/recipient addresses after address rewriting
+and alias expansion or forwarding, they also show information about
+delivery to mailbox, delivery to non-Postfix command, responses
+from remote SMTP servers, and so on.
+</p>
+
+<p> Postfix can produce two types of mail delivery reports for
+debugging: </p>
+
+<ul>
+
+<li> <p> What-if: report what would happen, but do not actually
+deliver mail. This mode of operation is requested with: </p>
+
+<pre>
+% <b>/usr/sbin/sendmail -bv address...</b>
+Mail Delivery Status Report will be mailed to &lt;your login name&gt;.
+</pre>
+
+<li> <p> What happened: deliver mail and report successes and/or
+failures, including replies from remote SMTP servers. This mode
+of operation is requested with: </p>
+
+<pre>
+% <b>/usr/sbin/sendmail -v address...</b>
+Mail Delivery Status Report will be mailed to &lt;your login name&gt;.
+</pre>
+
+</ul>
+
+<p> These reports contain information that is generated by Postfix
+delivery agents. Since these run as daemon processes that cannot
+interact with users directly, the result is sent as mail to the
+sender of the test message. The format of these reports is practically
+identical to that of ordinary non-delivery notifications. </p>
+
+<p> For a detailed example of a mail delivery status report, see
+the <a href="ADDRESS_REWRITING_README.html#debugging"> debugging</a>
+section at the end of the ADDRESS_REWRITING_README document. </p>
+
+<h2><a name="no_chroot">Try turning off chroot operation in master.cf</a></h2>
+
+<p> A common mistake is to turn on chroot operation in the master.cf
+file without going through all the necessary steps to set up a
+chroot environment. This causes Postfix daemon processes to fail
+due to all kinds of missing files. </p>
+
+<p> The example below shows an SMTP server that is configured with
+chroot turned off: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/master.cf:
+ # =============================================================
+ # service type private unpriv <b>chroot</b> wakeup maxproc command
+ # (yes) (yes) <b>(yes)</b> (never) (100)
+ # =============================================================
+ smtp inet n - <b>n</b> - - smtpd
+</pre>
+</blockquote>
+
+<p> Inspect master.cf for any processes that have chroot operation
+not turned off. If you find any, save a copy of the master.cf file,
+and edit the entries in question. After executing the command
+"<b>postfix reload</b>", see if the problem has gone away. </p>
+
+<p> If turning off chrooted operation made the problem go away,
+then congratulations. Leaving Postfix running in this way is
+adequate for most sites. If you prefer chrooted operation, see
+the Postfix <a href="BASIC_CONFIGURATION_README.html#chroot_setup">
+BASIC_CONFIGURATION_README</a> file for information about how to
+prepare Postfix for chrooted operation. </p>
+
+<h2><a name="debug_peer">Verbose logging for specific SMTP
+connections</a></h2>
+
+<p> In /etc/postfix/main.cf, list the remote site name or address
+in the debug_peer_list parameter. For example, in order to make
+the software log a lot of information to the syslog daemon for
+connections from or to the loopback interface: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ debug_peer_list = 127.0.0.1
+</pre>
+</blockquote>
+
+<p> You can specify one or more hosts, domains, addresses or
+net/masks. To make the change effective immediately, execute the
+command "<b>postfix reload</b>". </p>
+
+<h2><a name="sniffer">Record the SMTP session with a network sniffer</a></h2>
+
+<p> This example uses <b>tcpdump</b>. In order to record a conversation
+you need to specify a large enough buffer with the "<b>-s</b>"
+option or else you will miss some or all of the packet payload.
+</p>
+
+<blockquote>
+<pre>
+# <b>tcpdump -w /file/name -s 0 host example.com and port 25</b>
+</pre>
+</blockquote>
+
+<p> Older tcpdump versions don't support "<b>-s 0</b>"; in that case,
+use "<b>-s 2000</b>" instead. </p>
+
+<p> Run this for a while, stop with Ctrl-C when done. To view the
+data use a binary viewer, <b>ethereal</b>, or good old <b>less</b>.
+</p>
+
+<h2><a name="verbose">Making Postfix daemon programs more verbose</a></h2>
+
+<p> Append one or more "<b>-v</b>" options to selected daemon
+definitions in /etc/postfix/master.cf and type "<b>postfix reload</b>".
+This will cause a lot of activity to be logged to the syslog daemon.
+For example, to make the Postfix SMTP server process more verbose: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/master.cf:
+ smtp inet n - n - - smtpd -v
+</pre>
+</blockquote>
+
+<p> To diagnose problems with address rewriting specify a "<b>-v</b>"
+option for the cleanup(8) and/or trivial-rewrite(8) daemon, and to
+diagnose problems with mail delivery specify a "<b>-v</b>"
+option for the qmgr(8) or oqmgr(8) queue manager, or for the lmtp(8),
+local(8), pipe(8), smtp(8), or virtual(8) delivery agent. </p>
+
+<h2><a name="man_trace">Manually tracing a Postfix daemon process</a></h2>
+
+<p> Many systems allow you to inspect a running process with a
+system call tracer. For example: </p>
+
+<blockquote>
+<pre>
+# <b>trace -p process-id</b> (SunOS 4)
+# <b>strace -p process-id</b> (Linux and many others)
+# <b>truss -p process-id</b> (Solaris, FreeBSD)
+# <b>ktrace -p process-id</b> (generic 4.4BSD)
+</pre>
+</blockquote>
+
+<p> Even more informative are traces of system library calls.
+Examples: </p>
+
+<blockquote>
+<pre>
+# <b>ltrace -p process-id</b> (Linux, also ported to FreeBSD and BSD/OS)
+# <b>sotruss -p process-id</b> (Solaris)
+</pre>
+</blockquote>
+
+<p> See your system documentation for details. </p>
+
+<p> Tracing a running process can give valuable information about
+what a process is attempting to do. This is as much information as
+you can get without running an interactive debugger program, as
+described in a later section. </p>
+
+<h2><a name="auto_trace">Automatically tracing a Postfix daemon
+process</a></h2>
+
+<p> Postfix can attach a call tracer whenever a daemon process
+starts. Call tracers come in several kinds. </p>
+
+<ol>
+
+<li> <p> System call tracers such as <b>trace</b>, <b>truss</b>,
+<b>strace</b>, or <b>ktrace</b>. These show the communication
+between the process and the kernel. </p>
+
+<li> <p> Library call tracers such as <b>sotruss</b> and <b>ltrace</b>.
+These show calls of library routines, and give a better idea of
+what is going on within the process. </p>
+
+</ol>
+
+<p> Append a <b>-D</b> option to the suspect command in
+/etc/postfix/master.cf, for example: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/master.cf:
+ smtp inet n - n - - smtpd -D
+</pre>
+</blockquote>
+
+<p> Edit the debugger_command definition in /etc/postfix/main.cf
+so that it invokes the call tracer of your choice, for example:
+</p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ debugger_command =
+ PATH=/bin:/usr/bin:/usr/local/bin;
+ (truss -p $process_id 2&gt;&amp;1 | logger -p mail.info) &amp; sleep 5
+</pre>
+</blockquote>
+
+<p> Type "<b>postfix reload</b>" and watch the logfile. </p>
+
+<h2><a name="ddd">Running daemon programs with the interactive
+ddd debugger</a></h2>
+
+<p> If you have X Windows installed on the Postfix machine, then
+an interactive debugger such as <b>ddd</b> can be convenient.
+</p>
+
+<p> Edit the debugger_command definition in /etc/postfix/main.cf
+so that it invokes <b>ddd</b>: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ debugger_command =
+ PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin
+ ddd $daemon_directory/$process_name $process_id &amp; sleep 5
+</pre>
+</blockquote>
+
+<p> Be sure that <b>gdb</b> is in the command search path, and
+export <b>XAUTHORITY</b> so that X access control works, for example:
+</p>
+
+<blockquote>
+<pre>
+% <b>setenv XAUTHORITY ~/.Xauthority</b> (csh syntax)
+$ <b>export XAUTHORITY=$HOME/.Xauthority</b> (sh syntax)
+</pre>
+</blockquote>
+
+<p> Append a <b>-D</b> option to the suspect daemon definition in
+/etc/postfix/master.cf, for example: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/master.cf:
+ smtp inet n - n - - smtpd -D
+</pre>
+</blockquote>
+
+<p> Stop and start the Postfix system. This is necessary so that
+Postfix runs with the proper <b>XAUTHORITY</b> and <b>DISPLAY</b>
+settings. </p>
+
+<p> Whenever the suspect daemon process is started, a debugger
+window pops up and you can watch in detail what happens. </p>
+
+<h2><a name="screen">Running daemon programs with the interactive
+gdb debugger</a></h2>
+
+<p> If you have the screen command installed on the Postfix machine, then
+you can run an interactive debugger such as <b>gdb</b> as follows. </p>
+
+<p> Edit the debugger_command definition in /etc/postfix/main.cf
+so that it runs <b>gdb</b> inside a detached <b>screen</b> session:
+</p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ debugger_command =
+ PATH=/bin:/usr/bin:/sbin:/usr/sbin; export PATH; HOME=/root;
+ export HOME; screen -e^tt -dmS $process_name gdb
+ $daemon_directory/$process_name $process_id &amp; sleep 2
+</pre>
+</blockquote>
+
+<p> Be sure that <b>gdb</b> is in the command search path. </p>
+
+<p> Append a <b>-D</b> option to the suspect daemon definition in
+/etc/postfix/master.cf, for example: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/master.cf:
+ smtp inet n - n - - smtpd -D
+</pre>
+</blockquote>
+
+<p> Execute the command "<b>postfix reload</b>" and wait until a
+daemon process is started (you can see this in the maillog file).
+</p>
+
+<p> Then attach to the screen, and debug away: </p>
+
+<blockquote>
+<pre>
+# HOME=/root screen -r
+gdb) continue
+gdb) where
+</pre>
+</blockquote>
+
+<h2><a name="gdb">Running daemon programs under a non-interactive
+debugger</a></h2>
+
+<p> If you do not have X Windows installed on the Postfix machine,
+or if you are not familiar with interactive debuggers, then you
+can try to run <b>gdb</b> in non-interactive mode, and have it
+print a stack trace when the process crashes. </p>
+
+<p> Edit the debugger_command definition in /etc/postfix/main.cf
+so that it invokes the <b>gdb</b> debugger: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ debugger_command =
+ PATH=/bin:/usr/bin:/usr/local/bin; export PATH; (echo cont; echo
+ where; sleep 8640000) | gdb $daemon_directory/$process_name
+ $process_id 2&gt&amp;1
+ &gt;$config_directory/$process_name.$process_id.log &amp; sleep 5
+</pre>
+</blockquote>
+
+<p> Append a <b>-D</b> option to the suspect daemon in
+/etc/postfix/master.cf, for example: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/master.cf:
+ smtp inet n - n - - smtpd -D
+</pre>
+</blockquote>
+
+<p> Type "<b>postfix reload</b>" to make the configuration changes
+effective. </p>
+
+<p> Whenever a suspect daemon process is started, an output file
+is created, named after the daemon and process ID (for example,
+smtpd.12345.log). When the process crashes, a stack trace (with
+output from the "<b>where</b>" command) is written to its logfile.
+</p>
+
+<h2><a name="unreasonable">Unreasonable behavior</a></h2>
+
+<p> Sometimes the behavior exhibited by Postfix just does not match the
+source code. Why can a program deviate from the instructions given
+by its author? There are two possibilities. </p>
+
+<ul>
+
+<li> <p> The compiler has erred. This rarely happens. </p>
+
+<li> <p> The hardware has erred. Does the machine have ECC memory? </p>
+
+</ul>
+
+<p> In both cases, the program being executed is not the program
+that was supposed to be executed, so anything could happen. </p>
+
+<p> There is a third possibility: </p>
+
+<ul>
+
+<li> <p> Bugs in system software (kernel or libraries). </p>
+
+</ul>
+
+<p> Hardware-related failures usually do not reproduce in exactly
+the same way after power cycling and rebooting the system. There's
+little Postfix can do about bad hardware. Be sure to use hardware
+that at the very least can detect memory errors. Otherwise, Postfix
+will just be waiting to be hit by a bit error. Critical systems
+deserve real hardware. </p>
+
+<p> When a compiler makes an error, the problem can be reproduced
+whenever the resulting program is run. Compiler errors are most
+likely to happen in the code optimizer. If a problem is reproducible
+across power cycles and system reboots, it can be worthwhile to
+rebuild Postfix with optimization disabled, and to see if optimization
+makes a difference. </p>
+
+<p> In order to compile Postfix with optimizations turned off: </p>
+
+<blockquote>
+<pre>
+% <b>make tidy</b>
+% <b>make makefiles OPT=</b>
+</pre>
+</blockquote>
+
+<p> This produces a set of Makefiles that do not request compiler
+optimization. </p>
+
+<p> Once the makefiles are set up, build the software: </p>
+
+<blockquote>
+<pre>
+% <b>make</b>
+% <b>su</b>
+Password:
+# <b>make install</b>
+</pre>
+</blockquote>
+
+<p> If the problem goes away, then it is time to ask your vendor
+for help. </p>
+
+<h2><a name="mail">Reporting problems to postfix-users@postfix.org</a></h2>
+
+<p> The people who participate on postfix-users@postfix.org
+are very helpful, especially if YOU provide them with sufficient
+information. Remember, these volunteers are willing to help, but
+their time is limited. </p>
+
+<p> When reporting a problem, be sure to include the following
+information. </p>
+
+<ul>
+
+<li> <p> A summary of the problem. Please do not just send some
+logging without explanation of what YOU believe is wrong. </p>
+
+<li> <p> Complete error messages. Please use cut-and-paste, or use
+attachments, instead of reciting information from memory.
+</p>
+
+<li> <p> Postfix logging. See the text at the top of the DEBUG_README
+document to find out where logging is stored. Please do not frustrate
+the helpers by word wrapping the logging. If the logging is more
+than a few kbytes of text, consider posting an URL on a web or ftp
+site. </p>
+
+<li> <p> Consider using a test email address so that you don't have
+to reveal email addresses or passwords of innocent people. </p>
+
+<li> <p> If you can't use a test email address, please anonymize
+email addresses and host names consistently. Replace each letter
+by "A", each digit
+by "D" so that the helpers can still recognize syntactical errors.
+</p>
+
+<li> <p> Command output from:</p>
+
+<ul>
+
+<li> <p> "<b>postconf -n</b>". Please do not send your main.cf file,
+or 1000+ lines of <b>postconf</b> command output. </p>
+
+<li> <p> "<b>postconf -Mf</b>" (Postfix 2.9 or later). </p>
+
+</ul>
+
+<li> <p> Better, provide output from the <b>postfinger</b> tool.
+This can be found at http://ftp.wl0.org/SOURCES/postfinger. </p>
+
+<li> <p> If the problem is SASL related, consider including the
+output from the <b>saslfinger</b> tool. This can be found at
+http://postfix.state-of-mind.de/patrick.koetter/saslfinger/. </p>
+
+<li> <p> If the problem is about too much mail in the queue, consider
+including output from the <b>qshape</b> tool, as described in the
+QSHAPE_README file. </p>
+
+<li> <p> If the problem is protocol related (connections time out,
+or an SMTP server complains about syntax errors etc.) consider
+recording a session with <b>tcpdump</b>, as described in the <a
+href="#sniffer">DEBUG_README</a> document. </ul>
+
+</body>
+
+</html>