How to turn on PHP error display for development

Error display is a single switch in Server by Zaweba. Open the PHP page, choose the PHP version your site runs on and turn on display_errors. After the graceful Apache restart that follows, PHP prints its warnings and errors in the page itself, so you see what went wrong instead of a blank screen.

On a live website you want errors hidden, because they can show file paths and other details to strangers. On your own PC it's the other way round. While you're writing code you want every mistake spelled out where you're looking, and that's what display_errors does.

Where the switch is

The PHP page edits each PHP version on its own. Server includes 5.6, 7.4, 8.2 and 8.3, each with its own php.ini, and each has its own display_errors switch. That means you can show errors for the version you're developing on while leaving the others as they are. Check the site's version in the sites list before you flip the switch, because turning it on for the wrong version changes nothing you can see.

Server writes the change as one line in that version's php.ini, leaving the rest of the file alone. Apache restarts gracefully shortly afterwards, then a refresh of your page shows the messages.

Reading what PHP tells you

An error message names the problem, the file and the line number. Go to that line first, but remember the real cause is sometimes a line or two above it: a missing semicolon or bracket often only shows up where PHP gives up.

Warnings and notices are worth reading too. They don't stop the page, but they point at things like a variable used before it was set, which tends to become a real bug later. Clearing them as you go keeps the code tidy.

If a page still comes up blank with the switch on, the error may have happened before PHP could print anything, or it may be in code that runs during a redirect. The Logs page has the error log for each PHP version, following new lines as they arrive, and it catches what never reached the browser.

Showing errors and keeping a log

The two work well together. Display is quick for the page in front of you. The log keeps a record, which helps with background jobs, form posts that redirect, and anything that runs when you're not watching. The Logs page can clear a log so you start fresh before a test, and open the logs folder if you want the files themselves.

Apache's error log sits alongside on the same page. When a page fails before PHP is involved at all, for example because of a rewrite rule, that's where the reason appears.

Before your code goes live

Errors showing in the page are a development tool, not something for visitors. When you move a site to a web host, make sure display_errors is off there and errors go to a log instead. Your host's own settings control that, not your local ones.

It also helps to test with the switch off once before you upload. A page that relies on a notice being printed, or that looks fine only because an error message pushed something down, will look different without it. Turn the switch off on the PHP page, refresh, and check the page still behaves.

Other settings close by

The same page holds memory_limit, the upload size, max_execution_time and date.timezone, plus a tick box for every extension. If an error says a function doesn't exist, it's often an extension that needs ticking. If it says memory was exhausted or the time limit was reached, the boxes beside it are the place to look.

With display on, the log open and the right version chosen, most PHP mistakes take minutes to find in Server by Zaweba rather than an afternoon.