---
title: PHP Troubleshooting
eleventyNavigation:
  key: PHP Troubleshooting
  parent: PHP
  order: 99
---

## mod_fcgid: can't apply process slot

This error message returned by the Apache log (`/home/[account]/admin/logs/apache/`) indicates that the limit on the number of PHP processes (*dependent on the chosen package*) at a given time has been reached and that new connections are waiting for a PHP process to become available.

To quickly restart the site you can do it in **Web > Sites**. This will however only "artificially" and temporarily fix the problem. You can [analyze the processes](/en/docs/web-hosting/sites/customizing/analyze-processes) or use PHP profiling services such as [New Relic](https://newrelic.com/products/application-monitoring), [Tideways](https://tideways.com/) or [Blackfire](https://blackfire.io/) to find the source.

There can be many reasons: lack of optimization, unreachable external resource, session problem...

### Blocked sessions

Every time a PHP session is started, a file is created (`session.save_path`) comprising all of its information and allocating it an ID. When a user returns, they provide this ID so that `session_start()` can retrieve the session data. Every time `session_start()` is started, the session file is locked using `flock`.

This may cause problems when two PHP processes attempt to simultaneously access the same PHP session: the second has to wait until the first one ends before it can run to avoid competitive incidents. Consequently, this causes slowdowns or unavailabilities.

The analysis of your HTTP processes returns:

```sh
$ strace -f -p1821543 -p1822026 
Process 1821543 attached
Process 1822026 attached
[pid 1821543] flock(8, LOCK_EX <unfinished ...>
[pid 1822026] flock(8, LOCK_EX
```

> [!TIP]
> This [documentation](https://ma.ttias.be/php-session-locking-prevent-sessions-blocking-in-requests/) will provide you with more information and solutions for correcting these problem sessions. The best practice, to limit the period during which the session is locked, is to call `session_start()` as late as possible and `session_close()` as early as possible.


In case of *extreme necessity*, it is possible to set the configuration option `session.disable_locking` to `1` to remove any possibility of *lock*. **WARNING**, this can **corrupt sessions** and therefore lead to complications.

## Error messages

### Fatal error: Allowed memory size of 268435456 bytes exhausted

You have reached the 256 Mbyte limit, the default value for `memory_limit` in PHP. You can increase this value via the `php.ini` in **Environment > PHP** or from the site itself in **Web > Sites > Modify the [site] - ⚙️**.

## Use several versions in SSH

To use in SSH another PHP version and/or configuration than the one indicated in **Environment > PHP**, it is possible to use the following commands:

```sh
$ export PHP_VERSION=<version>
$ export PHPRC=/path/to/php.ini
```

or else for the `php.ini`:

```sh
$ php -c /path/to/php.ini
```

The `php.ini` files are available in read-only in the directory `/home/[account]/admin/config/php/`.