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<link rel='stylesheet' type='text/css' href='postfix-doc.css'> 12 13</head> 14 15<body> 16 17<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix and Linux</h1> 18 19<hr> 20 21<h2> Host lookup issues </h2> 22 23<p> By default Linux /etc/hosts lookups do not support multiple IP 24addresses per hostname. This causes warnings from the Postfix SMTP 25server that "hostname XXX does not resolve to address YYY", and is 26especially a problem with hosts that have both IPv4 and IPv6 27addresses. To fix this, turn on support for multiple IP addresses: </p> 28 29<blockquote> 30<pre> 31/etc/host.conf: 32 ... 33 # We have machines with multiple IP addresses. 34 multi on 35 ... 36</pre> 37</blockquote> 38 39<p> Alternatively, specify the RESOLV_MULTI environment variable 40in <a href="postconf.5.html">main.cf</a>: </p> 41 42<blockquote> 43<pre> 44/etc/postfix/<a href="postconf.5.html">main.cf</a>: 45 <a href="postconf.5.html#import_environment">import_environment</a> = MAIL_CONFIG MAIL_DEBUG MAIL_LOGTAG TZ XAUTHORITY DISPLAY LANG=C RESOLV_MULTI=on 46</pre> 47</blockquote> 48 49<h2>Berkeley DB issues</h2> 50 51<p> If you can't compile Postfix because the file "db.h" 52isn't found, then you MUST install the Berkeley DB development 53package (name: db???-devel-???) that matches your system library. 54You can find out what is installed with the rpm command. For example: 55</p> 56 57<blockquote> 58<pre> 59$ <b>rpm -qf /usr/lib/libdb.so</b> 60db4-4.3.29-2 61</pre> 62</blockquote> 63 64<p> This means that you need to install db4-devel-4.3.29-2 (on 65some systems, specify "<b>rpm -qf /lib/libdb.so</b>" instead). </p> 66 67<p> DO NOT download some Berkeley DB version from the network. 68Every Postfix program will dump core when it is built with a different 69Berkeley DB version than the version that is used by the system 70library routines. See the <a href="DB_README.html">DB_README</a> file for further information. 71</p> 72 73<h2>Procmail issues</h2> 74 75<p> On RedHat Linux 7.1 and later <b>procmail</b> no longer has 76permission 77to write to the mail spool directory. Workaround: </p> 78 79<blockquote> 80<pre> 81# chmod 1777 /var/spool/mail 82</pre> 83</blockquote> 84 85<h2>Logging in a container</h2> 86 87<p> When running Postfix inside a container, you can use stdout 88logging as described in <a href="MAILLOG_README.html">MAILLOG_README</a>. Alternatives: run syslogd 89inside the container, or mount the host's syslog socket inside the 90container. </p> 91 92<h2>Syslogd performance</h2> 93 94<p> LINUX <b>syslogd</b> uses synchronous writes by default. Because 95of this, <b>syslogd</b> can actually use more system resources than 96Postfix. To avoid such badness, disable synchronous mail logfile 97writes by editing /etc/syslog.conf and by prepending a - to the 98logfile name: </p> 99 100<blockquote> 101<pre> 102/etc/syslog.conf: 103 mail.* -/var/log/mail.log 104</pre> 105</blockquote> 106 107<p> Send a "<b>kill -HUP</b>" to the <b>syslogd</b> to make the 108change effective. </p> 109 110<h2>Other logging performance issues</h2> 111 112<p> LINUX <b>systemd</b> intercepts all logging and enforces its 113own rate limits before handing off requests to a backend such as 114<b>rsyslogd</b> or <b>syslog-ng</b>. On a busy mail server this can 115result in information loss. As a workaround, you can use Postfix's 116built-in logging as described in <a href="MAILLOG_README.html">MAILLOG_README</a>. </p> 117 118</body> 119 120</html> 121
