PHP Stuck on Loading After Enabling Xdebug? Don't Panic, It Might Be Working Perfectly!

## The Problem As PHP developers, we rely on Xdebug for debugging our code. However, a frustrating issue sometimes occurs: after eagerly adding `xdebug.mode=debug` to `php.ini`, the entire PHP application becomes unresponsive. The browser tab just spins endlessly, eventually timing out. But as soon as you remove or comment out that line, everything goes back to normal. What's going on? Is it an Xdebug bug or a misconfiguration? Let's examine a typical configuration that causes this issue: ```ini zend_extension=xdebug.so xdebug.mode=debug xdebug.start_with_request = yes xdebug.client_host = host.docker.internal xdebug.client_port = 9003 xdebug.log = /phplogs/wiki.lib00/xdebug.log ``` --- ## Finding the Truth in the Logs When troubleshooting, logs are your best friend. A quick look at the Xdebug log file reveals critical clues: ```log [7] Log opened at 2025-11-06 19:02:33.063715 [7] [Step Debug] INFO: Connecting to configured address/port: host.docker.internal:9003. [7] [Step Debug] INFO: Connected to debugging client: host.docker.internal:9003 (through xdebug.client_host/xdebug.client_port). [7] [Step Debug] -> <init ... fileuri="file:///var/www/wiki.lib00.com/public/index.php" ...> ... [7] [Step Debug] <- step_into -i 10 [7] [Step Debug] -> <response ... command="step_into" transaction_id="10" status="break" reason="ok"><xdebug:message filename="file:///var/www/wiki.lib00.com/public/index.php" lineno="4"></xdebug:message></response> ... [7] [Step Debug] <- eval -i 13 -- KHN0cmluZykoJF9TRVJWRVJbJ1NFUlZFUl9OQU1FJ10p [7] [Step Debug] -> <response ...><property type="string" ...>< ![CDATA[ZHAtdC0wNjgubGliMDAuY29t]]></property></response> ``` The log clearly tells us: 1. **Connection Successful**: `Connected to debugging client: host.docker.internal:9003` indicates that Xdebug has successfully connected to a debugging client (usually your IDE, like PhpStorm or VS Code) listening on port 9003. 2. **Execution Paused**: `status="break"` is the most crucial piece of information. It means Xdebug has done exactly what it was told to do: it has **paused the execution of the PHP script** at the first possible breakpoint (in this case, line 4 of `index.php`). **Conclusion:** The so-called "infinite loading" or "hang" is not an error. It is the **expected behavior of Xdebug's step debugging feature working correctly**. The PHP process is faithfully waiting for your IDE to send the next command (e.g., "resume," "step over," "step into"), and therefore, it cannot finish the request and send a response to the browser. --- ## The Correct Solutions Understanding the cause, we can now choose the right solution based on our development needs. ### Solution 1: If You Actually Want to Debug This is the most direct scenario. Since Xdebug has paused the script, you just need to switch to your IDE and: - Click the **"Resume Program"** button (often F9 or F5), which will let the script continue until the next breakpoint or until it finishes. - Alternatively, use the step debugging controls (Step Over, Step Into) to analyze your code line by line. Once the script execution is complete, the browser page will load as expected. ### Solution 2: On-Demand Debugging (Highly Recommended Best Practice) In daily development, we don't want every single request to be intercepted, as this severely hampers productivity. We only want to initiate debugging when we need it. This can be achieved by changing the value of `start_with_request` from `yes` to `trigger`. Modify your `php.ini` configuration: ```ini xdebug.mode=debug ; Change 'yes' to 'trigger' xdebug.start_with_request = trigger xdebug.client_host = host.docker.internal xdebug.client_port = 9003 ``` The benefits are significant: - **No Interruption by Default**: Without a trigger, PHP requests are processed normally and quickly, as if debugging were off. - **Activate on Demand**: When you need to debug, you can activate it using a browser extension (like **Xdebug Helper**) or by adding a specific parameter to your URL (`?XDEBUG_SESSION_START=idekey`). Only then will Xdebug connect and pause the program, entering debug mode. This approach is highly recommended by the `DP@lib00` team as it perfectly balances routine development with in-depth debugging sessions. ### Solution 3: Temporarily Disable Step Debugging If you don't need step debugging at all right now and only want to use Xdebug's other features (like the enhanced `var_dump()` and more detailed error reporting), you can set `xdebug.mode` to `develop`. ```ini ; Change 'debug' to 'develop' or simply comment out the line xdebug.mode = develop ``` This is precisely why "deleting `xdebug.mode=debug` makes the program work again." --- ## Configuration Summary | `start_with_request` Setting | Behavior | Use Case | | :--- | :--- | :--- | | `yes` | Tries to start a debugging session for **every request** and pauses. | Rarely used, except for debugging specific background processes that cannot be triggered otherwise. | | `trigger` | Starts a debugging session and pauses **only when a trigger is detected** (e.g., via a browser extension). | **Highly Recommended**. The best choice for day-to-day web development. | Next time you encounter a page "hanging" because of Xdebug, first check if your IDE is waiting for your input, and then ensure your `xdebug.start_with_request` setting matches your current workflow. A technical tip from [wiki.lib00.com](https://wiki.lib00.com).