Debugging

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 Moodle.org 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:

NONE

Do not show any errors or warnings (Default)

ALL

Show all reasonable PHP debug messages

MINIMAL

Show only fatal errors

NORMAL

Show warnings, errors and notices

DEVELOPER

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.

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 translators.

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 http://.../admin/settings.php?section=debugging on your server. Sometimes that URL will work, even though the pages you need to go to 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 add the lines:

$CFG->debug = (E_ALL | E_STRICT); $CFG->debugdisplay = 1;

// 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 remove those lines again when you have finished diagnosing your problem.

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

See also

• Developers can also use XDEBUG (Installed as a module on the Apache server) to further dig into the code, step by step using an XDEBUG client application. Probably, as part of their favorite IDE. For example: NetBeans, phpStorm or...
• Debugging/Bug fixing as knowledge creation Information posted by Tim Hunt in Planet Moodle 28 November 2013.