<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <title>Postfix logging to file or stdout</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> </head> <body> <h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix logging to file or stdout</h1> <hr> <h2>Overview </h2> <p> Postfix supports it own logging system as an alternative to syslog (which remains the default). This is available with Postfix version 3.4 or later. </p> <p> Topics covered in this document: </p> <ul> <li><a href="#log-to-file">Configuring logging to file</a> <li><a href="#log-to-stdout">Configuring logging to stdout</a> <li><a href="#logrotate">Rotating logs </a> <li><a href="#limitations">Limitations</a> </ul> <h2> <a name="log-to-file"> Configuring logging to file </a> </h2> <p> Logging to file solves a usability problem for MacOS, and eliminates multiple problems for systemd-based systems. </p> <ol> <li> <p> Add the following line to <a href="master.5.html">master.cf</a> if not already present (note: there must be no whitespace at the start of the line): </p> <blockquote> <pre> postlog unix-dgram n - n - 1 postlogd </pre> </blockquote> <p> Note: the service type "<b>unix-dgram</b>" was introduced with Postfix 3.4. Remove the above line before backing out to an older Postfix version. </p> <li> <p> Configure Postfix to write logging, to, for example, /var/log/postfix.log. See also the "<a href="#logrotate">Logfile rotation</a>" section below for logfile management. </p> <blockquote> <pre> # postfix stop # postconf <a href="postconf.5.html#maillog_file">maillog_file</a>=/var/log/postfix.log # postfix start </pre> </blockquote> <p> By default, the logfile name must start with "/var" or "/dev/stdout" (the list of allowed prefixes is configured with the <a href="postconf.5.html#maillog_file_prefixes">maillog_file_prefixes</a> parameter). This safety mechanism limits the damage from a single configuration mistake. </p> </ol> <h2> <a name="log-to-stdout"> Configuring logging to stdout </a> </h2> <p> Logging to stdout is useful when Postfix runs in a container, as it eliminates a syslogd dependency. </p> <ol> <li> <p> Add the following line to <a href="master.5.html">master.cf</a> if not already present (note: there must be no whitespace at the start of the line): </p> <blockquote> <pre> postlog unix-dgram n - n - 1 postlogd </pre> </blockquote> <p> Note: the service type "<b>unix-dgram</b>" was introduced with Postfix 3.4. Remove the above line before backing out to an older Postfix version. </p> <li> <p> Configure <a href="postconf.5.html">main.cf</a> with "<a href="postconf.5.html#maillog_file">maillog_file</a> = /dev/stdout". </p> <li> <p> Start Postfix with "<b>postfix start-fg</b>". </p> </ol> <h2> <a name="logrotate"> Rotating logs </a> </h2> <p> The command "<b>postfix logrotate</b>" may be run by hand or by a cronjob. It logs all errors, and reports errors to stderr if run from a terminal. This command implements the following steps: </p> <ul> <li> <p> Rename the current logfile by appending a suffix that contains the date and time. This suffix is configured with the <a href="postconf.5.html#maillog_file_rotate_suffix">maillog_file_rotate_suffix</a> parameter (default: %Y%m%d-%H%M%S). </p> <li> <p> Reload Postfix so that <a href="postlogd.8.html">postlogd(8)</a> immediately closes the old logfile. </p> <li> <p> After a brief pause, compress the old logfile. The compression program is configured with the <a href="postconf.5.html#maillog_file_compressor">maillog_file_compressor</a> parameter (default: gzip). </p> </ul> <p> Notes: </p> <ul> <li> <p> This command will not rotate a logfile with a pathname under the /dev directory, such as /dev/stdout. </p> <li> <p> This command does not (yet) remove old logfiles. </p> </ul> <h2> <a name="limitations">Limitations</a> </h2> <p> Background: </p> <ul> <li> <p> Postfix consists of a number of daemon programs that run in the background, as well as non-daemon programs for local mail submission or Postfix management. <li> <p> Logging to the Postfix logfile or stdout requires the Postfix <a href="postlogd.8.html">postlogd(8)</a> service. This ensures that simultaneous logging from different programs will not get mixed up. </p> <li> <p> All Postfix programs can log to syslog, but not all programs have sufficient privileges to use the Postfix logging service, and many non-daemon programs must not log to stdout as that would corrupt their output. </p> </ul> <p> Limitations: </p> <ul> <li> <p> Non-daemon Postfix programs will log errors to syslogd(8) before they have processed command-line options and <a href="postconf.5.html">main.cf</a> parameters. <li> <p> If Postfix is down, the non-daemon programs <a href="postfix.1.html">postfix(1)</a>, <a href="postsuper.1.html">postsuper(1)</a>, <a href="postmulti.1.html">postmulti(1)</a>, and <a href="postlog.1.html">postlog(1)</a>, will log directly to $<a href="postconf.5.html#maillog_file">maillog_file</a>. These programs expect to run with root privileges, for example during Postfix start-up, reload, or shutdown. <li> <p> Other non-daemon Postfix programs will never write directly to $<a href="postconf.5.html#maillog_file">maillog_file</a> (also, logging to stdout would interfere with the operation of some of these programs). These programs can log to <a href="postlogd.8.html">postlogd(8)</a> if they are run by the super-user, or if their executable file has set-gid permission. Do not set this permission on programs other than <a href="postdrop.1.html">postdrop(1)</a> and <a href="postqueue.1.html">postqueue(1)</a>. </ul> </body> </html>