From a848231ae0f346dc7cc000973fbeb65b0894ee92 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 10 Apr 2024 21:59:03 +0200 Subject: Adding upstream version 3.8.5. Signed-off-by: Daniel Baumann --- html/DEBUG_README.html | 598 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 598 insertions(+) create mode 100644 html/DEBUG_README.html (limited to 'html/DEBUG_README.html') diff --git a/html/DEBUG_README.html b/html/DEBUG_README.html new file mode 100644 index 0000000..a27d2ad --- /dev/null +++ b/html/DEBUG_README.html @@ -0,0 +1,598 @@ + + + + + + + Postfix Debugging Howto + + + + + + + + +

Postfix Debugging Howto

+ +
+ +

Purpose of this document

+ +

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.

+ +

The text assumes that the Postfix main.cf and master.cf +configuration files are stored in directory /etc/postfix. You can +use the command "postconf config_directory" to find out the +actual location of this directory on your machine.

+ +

Listed in order of increasing invasiveness, the debugging +techniques are as follows:

+ + + +

Look for obvious signs of trouble

+ +

Postfix logs all failed and successful deliveries to a logfile.

+ + + +

When Postfix does not receive or deliver mail, the first order +of business is to look for errors that prevent Postfix from working +properly:

+ +
+
+% grep -E '(warning|error|fatal|panic):' /some/log/file | more
+
+
+ +

Note: the most important message is near the BEGINNING of the +output. Error messages that come later are less useful.

+ +

The nature of each problem is indicated as follows:

+ + + +

Debugging Postfix from inside

+ +

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. +

+ +

Postfix can produce two types of mail delivery reports for +debugging:

+ + + +

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.

+ +

For a detailed example of a mail delivery status report, see +the debugging +section at the end of the ADDRESS_REWRITING_README document.

+ +

Try turning off chroot operation in master.cf

+ +

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.

+ +

The example below shows an SMTP server that is configured with +chroot turned off:

+ +
+
+/etc/postfix/master.cf:
+    # =============================================================
+    # service type  private unpriv  chroot  wakeup  maxproc command
+    #               (yes)   (yes)   (yes)   (never) (100)
+    # =============================================================
+    smtp      inet  n       -       n       -       -       smtpd
+
+
+ +

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 +"postfix reload", see if the problem has gone away.

+ +

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 +BASIC_CONFIGURATION_README file for information about how to +prepare Postfix for chrooted operation.

+ +

Verbose logging for specific SMTP +connections

+ +

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:

+ +
+
+/etc/postfix/main.cf:
+    debug_peer_list = 127.0.0.1
+
+
+ +

You can specify one or more hosts, domains, addresses or +net/masks. To make the change effective immediately, execute the +command "postfix reload".

+ +

Record the SMTP session with a network sniffer

+ +

This example uses tcpdump. In order to record a conversation +you need to specify a large enough buffer with the "-s" +option or else you will miss some or all of the packet payload. +

+ +
+
+# tcpdump -w /file/name -s 0 host example.com and port 25
+
+
+ +

Older tcpdump versions don't support "-s 0"; in that case, +use "-s 2000" instead.

+ +

Run this for a while, stop with Ctrl-C when done. To view the +data use a binary viewer, ethereal, or good old less. +

+ +

Making Postfix daemon programs more verbose

+ +

Append one or more "-v" options to selected daemon +definitions in /etc/postfix/master.cf and type "postfix reload". +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:

+ +
+
+/etc/postfix/master.cf:
+    smtp      inet  n       -       n       -       -       smtpd -v
+
+
+ +

To diagnose problems with address rewriting specify a "-v" +option for the cleanup(8) and/or trivial-rewrite(8) daemon, and to +diagnose problems with mail delivery specify a "-v" +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.

+ +

Manually tracing a Postfix daemon process

+ +

Many systems allow you to inspect a running process with a +system call tracer. For example:

+ +
+
+# trace -p process-id (SunOS 4)
+# strace -p process-id (Linux and many others)
+# truss -p process-id (Solaris, FreeBSD)
+# ktrace -p process-id (generic 4.4BSD)
+
+
+ +

Even more informative are traces of system library calls. +Examples:

+ +
+
+# ltrace -p process-id (Linux, also ported to FreeBSD and BSD/OS)
+# sotruss -p process-id (Solaris)
+
+
+ +

See your system documentation for details.

+ +

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.

+ +

Automatically tracing a Postfix daemon +process

+ +

Postfix can attach a call tracer whenever a daemon process +starts. Call tracers come in several kinds.

+ +
    + +

  1. System call tracers such as trace, truss, +strace, or ktrace. These show the communication +between the process and the kernel.

    + +

  2. Library call tracers such as sotruss and ltrace. +These show calls of library routines, and give a better idea of +what is going on within the process.

    + +
+ +

Append a -D option to the suspect command in +/etc/postfix/master.cf, for example:

+ +
+
+/etc/postfix/master.cf:
+    smtp      inet  n       -       n       -       -       smtpd -D
+
+
+ +

Edit the debugger_command definition in /etc/postfix/main.cf +so that it invokes the call tracer of your choice, for example: +

+ +
+
+/etc/postfix/main.cf:
+    debugger_command =
+         PATH=/bin:/usr/bin:/usr/local/bin;
+         (truss -p $process_id 2>&1 | logger -p mail.info) & sleep 5
+
+
+ +

Type "postfix reload" and watch the logfile.

+ +

Running daemon programs with the interactive +ddd debugger

+ +

If you have X Windows installed on the Postfix machine, then +an interactive debugger such as ddd can be convenient. +

+ +

Edit the debugger_command definition in /etc/postfix/main.cf +so that it invokes ddd:

+ +
+
+/etc/postfix/main.cf:
+    debugger_command =
+         PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin
+         ddd $daemon_directory/$process_name $process_id & sleep 5
+
+
+ +

Be sure that gdb is in the command search path, and +export XAUTHORITY so that X access control works, for example: +

+ +
+
+% setenv XAUTHORITY ~/.Xauthority (csh syntax)
+$ export XAUTHORITY=$HOME/.Xauthority (sh syntax)
+
+
+ +

Append a -D option to the suspect daemon definition in +/etc/postfix/master.cf, for example:

+ +
+
+/etc/postfix/master.cf:
+    smtp      inet  n       -       n       -       -       smtpd -D
+
+
+ +

Stop and start the Postfix system. This is necessary so that +Postfix runs with the proper XAUTHORITY and DISPLAY +settings.

+ +

Whenever the suspect daemon process is started, a debugger +window pops up and you can watch in detail what happens.

+ +

Running daemon programs with the interactive +gdb debugger

+ +

If you have the screen command installed on the Postfix machine, then +you can run an interactive debugger such as gdb as follows.

+ +

Edit the debugger_command definition in /etc/postfix/main.cf +so that it runs gdb inside a detached screen session: +

+ +
+
+/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 & sleep 2
+
+
+ +

Be sure that gdb is in the command search path.

+ +

Append a -D option to the suspect daemon definition in +/etc/postfix/master.cf, for example:

+ +
+
+/etc/postfix/master.cf:
+    smtp      inet  n       -       n       -       -       smtpd -D
+
+
+ +

Execute the command "postfix reload" and wait until a +daemon process is started (you can see this in the maillog file). +

+ +

Then attach to the screen, and debug away:

+ +
+
+# HOME=/root screen -r
+gdb) continue
+gdb) where
+
+
+ +

Running daemon programs under a non-interactive +debugger

+ +

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 gdb in non-interactive mode, and have it +print a stack trace when the process crashes.

+ +

Edit the debugger_command definition in /etc/postfix/main.cf +so that it invokes the gdb debugger:

+ +
+
+/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 
+        $process_id 2>&1
+        >$config_directory/$process_name.$process_id.log & sleep 5
+
+
+ +

Append a -D option to the suspect daemon in +/etc/postfix/master.cf, for example:

+ +
+
+/etc/postfix/master.cf:
+    smtp      inet  n       -       n       -       -       smtpd -D
+
+
+ +

Type "postfix reload" to make the configuration changes +effective.

+ +

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 "where" command) is written to its logfile. +

+ +

Unreasonable behavior

+ +

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.

+ + + +

In both cases, the program being executed is not the program +that was supposed to be executed, so anything could happen.

+ +

There is a third possibility:

+ + + +

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.

+ +

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.

+ +

In order to compile Postfix with optimizations turned off:

+ +
+
+% make tidy
+% make makefiles OPT=
+
+
+ +

This produces a set of Makefiles that do not request compiler +optimization.

+ +

Once the makefiles are set up, build the software:

+ +
+
+% make
+% su
+Password:
+# make install
+
+
+ +

If the problem goes away, then it is time to ask your vendor +for help.

+ +

Reporting problems to postfix-users@postfix.org

+ +

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.

+ +

When reporting a problem, be sure to include the following +information.

+ + + + + + -- cgit v1.2.3