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 and Linux</title> 9 10<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 11 12</head> 13 14<body> 15 16<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix and Linux</h1> 17 18<hr> 19 20<h2> Host lookup issues </h2> 21 22<p> By default Linux /etc/hosts lookups do not support multiple IP 23addresses per hostname. This causes warnings from the Postfix SMTP 24server that "hostname XXX does not resolve to address YYY", and is 25especially a problem with hosts that have both IPv4 and IPv6 26addresses. To fix this, turn on support for multiple IP addresses: </p> 27 28<blockquote> 29<pre> 30/etc/host.conf: 31 ... 32 # We have machines with multiple IP addresses. 33 multi on 34 ... 35</pre> 36</blockquote> 37 38<p> Alternatively, specify the RESOLV_MULTI environment variable 39in <a href="postconf.5.html">main.cf</a>: </p> 40 41<blockquote> 42<pre> 43/etc/postfix/<a href="postconf.5.html">main.cf</a>: 44 <a href="postconf.5.html#import_environment">import_environment</a> = MAIL_CONFIG MAIL_DEBUG MAIL_LOGTAG TZ XAUTHORITY DISPLAY LANG=C RESOLV_MULTI=on 45</pre> 46</blockquote> 47 48<h2>Berkeley DB issues</h2> 49 50<p> If you can't compile Postfix because the file "db.h" 51isn't found, then you MUST install the Berkeley DB development 52package (name: db???-devel-???) that matches your system library. 53You can find out what is installed with the rpm command. For example: 54</p> 55 56<blockquote> 57<pre> 58$ <b>rpm -qf /usr/lib/libdb.so</b> 59db4-4.3.29-2 60</pre> 61</blockquote> 62 63<p> This means that you need to install db4-devel-4.3.29-2 (on 64some systems, specify "<b>rpm -qf /lib/libdb.so</b>" instead). </p> 65 66<p> DO NOT download some Berkeley DB version from the network. 67Every Postfix program will dump core when it is built with a different 68Berkeley DB version than the version that is used by the system 69library routines. See the <a href="DB_README.html">DB_README</a> file for further information. 70</p> 71 72<h2>Procmail issues</h2> 73 74<p> On RedHat Linux 7.1 and later <b>procmail</b> no longer has 75permission 76to write to the mail spool directory. Workaround: </p> 77 78<blockquote> 79<pre> 80# chmod 1777 /var/spool/mail 81</pre> 82</blockquote> 83 84<h2>Logging in a container</h2> 85 86<p> When running Postfix inside a container, you can use stdout 87logging as described in <a href="MAILLOG_README.html">MAILLOG_README</a>. Alternatives: run syslogd 88inside the container, or mount the host's syslog socket inside the 89container. </p> 90 91<h2>Syslogd performance</h2> 92 93<p> LINUX <b>syslogd</b> uses synchronous writes by default. Because 94of this, <b>syslogd</b> can actually use more system resources than 95Postfix. To avoid such badness, disable synchronous mail logfile 96writes by editing /etc/syslog.conf and by prepending a - to the 97logfile name: </p> 98 99<blockquote> 100<pre> 101/etc/syslog.conf: 102 mail.* -/var/log/mail.log 103</pre> 104</blockquote> 105 106<p> Send a "<b>kill -HUP</b>" to the <b>syslogd</b> to make the 107change effective. </p> 108 109<h2>Other logging performance issues</h2> 110 111<p> LINUX <b>systemd</b> intercepts all logging and enforces its 112own rate limits before handing off requests to a backend such as 113<b>rsyslogd</b> or <b>syslog-ng</b>. On a busy mail server this can 114result in information loss. As a workaround, you can use Postfix's 115built-in logging as described in <a href="MAILLOG_README.html">MAILLOG_README</a>. </p> 116 117</body> 118 119</html> 120
