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PHP FPM 503 error – Let’s resolve it

Are you frustrated with the PHP FPM 503 error? We will help you fix it quickly.

When the Apache is not able to communicate with the PHP-FPM process manager, then it results in a 503 error.

At Bobcares, we often receive requests to fix this error as part of our Server Management Services.

Today, let’s have a deep look at this error and see how our Support Engineers fix this error easily.



Website performances are always a major concern. Isn’t it?

When we request data, the web server passes it to the application program. And, from there it receives the data and forwards it back to the user.

This is the common gateway interface(CGI) method. But, CGI based methods often face speed problems.

So, PHP-FPM (FastCGI Process Manager) is a popular web tool that speeds up the performance of a website. But, it often throws some tricky errors.


Causes and fixes of PHP FPM 503

Usually, this error can occur due to various reasons. Let’s now check the major causes of this error and see how our Support Engineers fix it easily.


1. Stopped PHP-FPM service

Recently, one of our customers approached us with a PHP FPM error.

He was using Plesk panel and when he tried to load his website, it showed up the below error.


His website used PHP-FPM handler at Domains > > PHP Settings.

Our Support Engineers checked the error in detail. On checking, we found that the error occurred when the PHM-FPM service has been stopped.

That is, Apache could not communicate to the PHP-FPM. Restarting the PHP-FPM will resolve the error easily.

We follow the below steps to restart it in Plesk.

  1. Firstly, we log in to the Plesk and check the version of the PHP-FPM.
  2. Then, navigate to Tools & Settings >> Services Management.
  3. Finally, restart the PHP-FPM service with the required version.

And, this resolved the error easily.


2. Multiple PHP services running

Sometimes, this error can occur when we try to switch from one PHP-FPM version to the other.

In such cases, we check whether multiple PHP-FPM services are running parallelly or not.

If so, then we disable mod of the older version and enable the newer one.  And, then the PHP FPM will work fine.


3. Configuration changes

PHP FPM 503 error could also occur due to configuration mistakes.

If the error remains even after the restart, we need to double-check the configuration changes that occurred.

For instance, setting enablereuse=on in the vhost configuration file will return this error if PHP-FPM is running via a Unix socket. Because the UDS doesn’t support connect reuse.

Here, UDS is Unix Domain Sockets. And this applies when PHP-FPM is running as a socket (.sock), instead of the default TCP port method.

So, to resolve the error, we need to remove enablereuse=on from the vhost configuration file.


[Need more assistance to fix this error?- We’re available 24/7.]



In short, the PHP-FPM 503 error occurs mainly when the PHM-FPM service has been stopped, multiple PHP services running in parallel and so on. In today’s writeup, we discussed how our Support Engineers fix this error for our customers easily.


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