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Debugging messages can be enabled by an administrator in Administration > Site administration > Development > Debugging.

Debugging messages are intended to help diagnose problems and/or help Moodle developers. If you have a problem with your Moodle site and ask for help in a forum, a developer may ask you to turn debug messages on, in order to locate the cause of the problem. By default Moodle does not show any error messages at all. If you are having problems (e.g. blank screens or incomplete screens) turning on debugging is usually the first thing to try.

Debugging settings

Here are the settings on the Debugging page:

Debug messages

The default is none, your choices are:

Do not show any errors or warnings (Default)
Show all reasonable PHP debug messages
Show only fatal errors
Show warnings, errors and notices
extra Moodle debug messages for developers

There is rarely any advantage in going to Developer level, unless you are a developer, in which case it is strongly recommended.

Once you have got the error message, and copied and pasted it somewhere. HIGHLY RECOMMENDED to turn Debug back to NONE. Debug messages can give clues to a hacker as to the setup of your site.

Display debug messages

There is an option to choose whether to display error messages or simply record them in the server logs.

Debug email sending

Determines whether or not to enable verbose debug information during sending of email messages to SMTP server.

More tools for debugging outgoing mail

You can also use the config.php file to turn on more "tools" which will assist you with debugging the outgoing emails (and SMTP server configuration).

Please note that these settings should never be used on a production site

  • Redirect all outgoing emails to a specific address:

Please note that with this setting enabled, users will not receive any e-mail.

// Divert all outgoing emails to this address to test and debug emailing features
// $CFG->divertallemailsto = 'root@localhost.local'; // NOT FOR PRODUCTION SERVERS!
  • Turn on the CRON debugging and run CLI cron.php script.
// Force developer level debug and add debug info to the output of cron
// $CFG->showcrondebugging = true;

And then use SSH (or putty.exe, on windows) to run:

you@moodle-server(/var/www/html/moodle)# php admin/cli/cron.php
  • Turn on verbose SMTP debugging and output it into system's error_log (code hack):

As suggested on Moodle's discussion forums: Open lib/moodlelib.php L5379 and change it to:

if (!empty($CFG->debugsmtp)) {
    $mailer->SMTPDebug = 1;  // 0 - no debug ... 4 - low level full debug
    $mailer->Debugoutput = "error_log";

See more info about SMTPDebug parameters & Debugoutput parameters Please remember that all SMTP content is included in this log. This may include links which include tokens, temporary passwords, and other similar information. This setting should not be enabled on production systems.

Performance info

The Performance info option determines whether performance info will be included in the footer of the standard theme (and some other themes). Performance info includes the time for the page to load, the amount of memory used to generate the page, cpu usage, load, and the record cache hit/miss ration.

If you add

define('MDL_PERF', true);
define('MDL_PERFDB', true);
define('MDL_PERFTOLOG', true);
define('MDL_PERFTOFOOT', true);

to your config.php file, then it will also count database queries. (This has to be in config.php, because Moodle starts doing DB queries before it loads the config information in the database!

Show origin of language strings

Helps with translation and also with Language customization. Sometimes
should be added; other times
. See the Wikipedia article Query string for details.

Show validator links

Be careful, read the warning.

Show page information

To show page information printed in the page footer.

What to do if you cannot get to the admin screens

If the error is stopping you even getting to the admin screens to turn on debugging, then you can set the debugging setting manually.

Try typing the URL directly

The debug settings are at the URL
on your server. Sometimes that URL will work, even though the pages you need to go to get there (for example the site front page) do not. So it is worth trying to enter that URL directly.

In config.php

In config.php you can uncomment lines (delete the // at the start of the line) under Section 7 to enable debugging for all or just specific users:

// 7. SETTINGS FOR DEVELOPMENT SERVERS - not intended for production use!!!
// Force a debugging mode regardless the settings in the site administration
// @error_reporting(E_ALL | E_STRICT);   // NOT FOR PRODUCTION SERVERS!
// @ini_set('display_errors', '1');         // NOT FOR PRODUCTION SERVERS!
// $CFG->debugdisplay = 1;              // NOT FOR PRODUCTION SERVERS!
// You can specify a comma separated list of user ids that that always see
// debug messages, this overrides the debug flag in $CFG->debug and $CFG->debugdisplay
// for these users only.
// $CFG->debugusers = '2';

Remember to comment those lines again (reinsert the // at the start of the line) when you have finished diagnosing your problem.

NOTE 1: do not try to modify the config database table directly, it will not work because the values are cached in MUC.

NOTE 2: if you find your config.php does not have the above settings (you have a cut down approx 30 lines config.php) look for a "config-dist.php" file that contains the full details. I would suggest transferring your details in the current config.php file you have into the full config file and renaming that one to "config.php".

See also