Display PHP errors to troubleshoot a blank page

Q: What do the most common errors mean?

The message starts with its level (Fatal error, Parse error, Warning), then gives the file and line involved. A few frequent cases: Message Likely cause What to do Allowed memory size of … bytes exhausted The script needs more memory than your plan provides. In PHP configuration, Memory boost raises it to 2048 MB for 24 hours, for the time of a migration or an import. If the error comes back afterwards, a plugin uses too much memory: disable or update it. Maximum execution time of … seconds exceeded The script runs longer than your plan's limit. Split the processing, or run it as a scheduled task. Call to undefined function …() The function does not exist in your PHP version (an old function that was removed, such as mysql_connect()), or it is disabled for security. Update your application. For a disabled function, see the Not recommended PHP functions block of PHP configuration. … has been disabled for security reasons The function is disabled for security.

A blank page, or a 500 error, instead of your website is most often caused by a PHP error that the server does not show to your visitors. To fix it, you first have to read it. The Apanel console offers two ways: the Error Log PHP log, which shows nothing to your visitors, and displaying errors in the page for a short time, which is more direct but visible to everyone.

In short: in Hosting management, Website card, open Logs files, Error Log PHP tab, then reload the blank page. Otherwise, turn on Display php errors in PHP configuration just long enough to read the error.

Requirements

A domain with web hosting in your Apanel console.

What to know before you start

Each domain has its own PHP configuration. Make the changes in the Hosting management of the domain that shows the blank page.
The PHP error reporting setting decides which errors are reported, on screen as well as in the log. On Disabled, PHP reports nothing: no display, no line in the log.
An error message displayed in the page is visible to all your visitors, and it reveals paths and details of your site. Prefer the log, and if you turn the display on, turn it off again as soon as you have read the error.
When a site is created, the console turns Display php errors on with Only script execution errors. These settings may have been changed since: check their current state before touching them, so you can put them back afterwards.

How do I read the PHP error in the log?

Log in to your Apanel console.
From the dashboard, click your domain name to open Hosting management.
In the Website card, click Logs files.
Open the first tab, Error Log PHP. The Content of file (200 lines max) block shows the end of the log, with the most recent entry at the bottom.
Reload the blank page in your browser, then reload the Log files page: the last line is the error you have just triggered.

Download complete file fetches the whole log, and Display old files opens the folder of previous logs in a new tab. Depending on your server, the page also offers the Error Log Apache and Access Log Apache tabs, or Slow PHP Log.

How do I display the error in the page?

If the log stays empty, or to see the error directly on the page concerned:

In Hosting management, Web technologies card, click PHP configuration.
In the PHP errors management block, note the current state of both settings.
Turn on Display php errors.
In PHP error reporting, choose All errors (or keep the current level if it is not Disabled).
Click Save. The console confirms with a success message.

The PHP errors management block of the PHP configuration screen, with Display php errors on and PHP error reporting on All errors

Reload the blank page: the error message now appears instead.
As soon as you have noted the error, go back to PHP configuration, put both settings back as they were and click Save.

What do the most common errors mean?

The message starts with its level (Fatal error, Parse error, Warning), then gives the file and line involved. A few frequent cases:

Message	Likely cause	What to do
`Allowed memory size of … bytes exhausted`	The script needs more memory than your plan provides.	In PHP configuration, Memory boost raises it to 2048 MB for 24 hours, for the time of a migration or an import. If the error comes back afterwards, a plugin uses too much memory: disable or update it.
`Maximum execution time of … seconds exceeded`	The script runs longer than your plan's limit.	Split the processing, or run it as a scheduled task.
`Call to undefined function …()`	The function does not exist in your PHP version (an old function that was removed, such as `mysql_connect()`), or it is disabled for security.	Update your application. For a disabled function, see the Not recommended PHP functions block of PHP configuration.
`… has been disabled for security reasons`	The function is disabled for security.	Same as above: Not recommended PHP functions block, to be enabled only if your application requires it.
`Parse error: syntax error, unexpected …`	A file contains a syntax error, often after a manual edit, or code too old for your PHP version.	Fix the file at the line given, or go back to the previous PHP version while you update your application.
`Failed opening required …` or `No such file or directory`	An expected file is missing, often after an incomplete FTP transfer.	Upload the file mentioned to the server again.

Troubleshooting

What you see	What to do
The page stays blank although Display php errors is on	PHP error reporting is on Disabled: choose All errors. Some applications also handle error display themselves in their own debug mode: see their documentation.
The Error Log PHP tab is empty	No error has been written: PHP error reporting may be on Disabled, or the error does not come from PHP. Look at the Error Log Apache tab if there is one: an error in a `.htaccess` file shows up there.
"An error occurred during the operation. Error code: …" after Save	The configuration could not be applied. Note the code and send it to our support team with your domain name.
The blank page appeared right after a PHP version change	Go back to the previous version in PHP configuration, then update your application before trying again.

Going further

Change the PHP version and configuration of your website, for every setting of the PHP configuration screen.
Schedule a task (cron job), for processing too long for a web page.
My website was hacked: what happens and what you need to do, if the blank page appeared without any change on your side.