How to Fix PHP Warning Session Start Open Failed  

A WordPress warning such as “PHP Warning: session_start(): open failed” can look far more serious than it actually is.

You may suddenly see an ugly warning at the top of your website, notice strange errors in your hosting logs, or find that a plugin has stopped working properly. The good news is that this problem is usually connected to one of a handful of issues: incorrect PHP session settings, a missing or unwritable temporary directory, bad file permissions, or a plugin attempting to start a PHP session incorrectly.

The important thing is not to start changing random WordPress files.

That can make things worse.

Instead, work through the likely causes one at a time.

What Does “Session Start Open Failed” Mean?

PHP sessions allow a website to temporarily store information while someone is using it.

For example, a plugin may use a PHP session to remember a visitor’s settings, maintain information during a checkout process, or keep temporary data between page requests.

When PHP runs:

session_start();

it needs somewhere to store the session information.

If PHP cannot access that location, you may see an error similar to:

PHP Warning: session_start(): open(/path/to/session/file, O_RDWR) failed: Permission denied

Or you might see:

session_start(): Failed to read session data

Another common version mentions that the session directory does not exist.

The exact wording matters because it can point directly toward the cause.

First, Check Whether WordPress Is Actually Broken

Before changing anything, visit your website in an incognito browser window.

Check the homepage.

Then test several important pages, including your contact page, login page and any shopping or membership functions you use.

If everything works and the warning only appears in your hosting error log, you may not have a serious front-end problem at all.

Your hosting company may still want the underlying warning fixed, but don’t panic.

If the warning appears publicly on your website, however, you should deal with it promptly.

Check Your PHP Version

Start with the basics.

Log into your hosting control panel and find the PHP settings. Depending on your hosting company, this could be called PHP Manager, MultiPHP Manager, PHP Configuration, or something similar.

Check which PHP version your WordPress installation is using.

Old PHP versions can cause compatibility problems, particularly when WordPress plugins and themes have been updated over time.

However, don’t blindly switch PHP versions on a busy production website.

Before making a change, create a backup.

If your hosting account provides a staging website, test the change there first.

Check the PHP Session Save Path

One of the most common causes of this warning is an incorrect PHP session save path.

PHP needs a directory where session files can be created and read.

The PHP setting is generally called:

session.save_path

If this points to a directory that doesn’t exist, PHP can’t write the session file.

If it points to a directory that exists but isn’t writable, you can receive a permissions-related warning.

You can usually check this through your hosting control panel or by asking your hosting provider to confirm the current session save path.

This is often faster than trying to diagnose server-level configuration yourself.

Check Whether the Session Directory Exists

Suppose the error contains something like:

session_start(): open(/var/lib/php/sessions/sess_xxxxx) failed

That path gives you an important clue.

PHP is trying to create or access a session file inside a particular directory.

If that directory has disappeared, wasn’t created correctly, or isn’t available to PHP, the warning makes sense.

This is where many WordPress users get stuck because the problem isn’t actually inside WordPress.

It’s a server configuration issue.

Your WordPress files may be perfectly healthy.

Check File and Folder Permissions

Permissions are another major suspect.

PHP must have permission to write session files to the configured session directory.

If permissions are too restrictive, PHP may return an error such as:

Permission denied

Don’t simply give everything 777 permissions.

That’s a common quick fix found in random forum posts, but it isn’t a good approach for a production website.

It can create unnecessary security problems.

Instead, use the permissions recommended by your hosting provider for the particular server environment.

If you’re unsure, contact support and give them the exact PHP warning from the error log.

They can normally identify the problem quickly.

WordPress Plugins Can Cause Session Warnings

Here’s an important point.

The server may be functioning correctly while a WordPress plugin is causing the warning.

Some plugins use PHP sessions even though WordPress itself generally relies on cookies and its own mechanisms for handling user state.

A poorly coded or outdated plugin can attempt to start a session at the wrong time.

It can also attempt to start one more than once.

This is particularly worth investigating if the warning appeared immediately after installing or updating a plugin.

Think back.

What changed immediately before the warning appeared?

That question can save you hours.

Temporarily Disable Plugins

If you can access the WordPress dashboard, go to:

Plugins → Installed Plugins

Temporarily deactivate recently installed or updated plugins.

Then test the website again.

If the warning disappears, reactivate the plugins one at a time.

This process can identify the culprit without requiring you to change your server configuration.

If you cannot access the WordPress dashboard, you may be able to disable plugins through your hosting file manager or database, depending on your setup.

Don’t delete anything.

Deactivation is enough for testing.

Look for a Plugin Calling session_start()

If you’re comfortable working with website files, you can search your plugin files for:

session_start();

This can help identify which plugin is attempting to start a PHP session.

Don’t edit the plugin immediately.

Instead, identify it first.

Once you’ve found the plugin, check whether an updated version is available. Plugin developers sometimes release updates specifically to address PHP compatibility problems.

If no update exists, contact the developer.

You can provide the exact warning, your PHP version and the plugin version.

That information is much more useful than simply saying, “The plugin is broken.”

Check Your wp-config.php File

Your WordPress wp-config.php file can also be worth checking, particularly if the website has been moved between hosting companies.

Look for unusual custom PHP configuration or code that has been added manually.

Don’t start adding random session configuration to the file just because you’ve seen it recommended online.

WordPress configuration files are important.

One incorrect line can create another problem while you’re trying to fix the first one.

If you don’t recognise a piece of code, make a backup before touching it.

What If the Website Was Recently Migrated?

Website migrations are another common cause.

You may have moved your WordPress website from one hosting company to another, changed server configurations, or restored a backup.

The old server might have used a session directory that doesn’t exist on the new server.

The result?

WordPress still works, but a plugin tries to use PHP sessions and PHP can’t find the expected storage location.

In that situation, your hosting provider may need to correct the PHP session configuration.

When You Should Contact Your Hosting Company

There is no prize for spending three hours fighting a server configuration problem.

If you’ve confirmed that a plugin isn’t responsible and the warning refers to PHP’s session directory, contact your host.

Send them the complete error message.

Also provide:

• Your PHP version
• The affected website
• The exact session warning
• Whether the website was recently migrated
• Whether the warning appears publicly or only in the error log

A competent hosting technician should be able to check the PHP session configuration, directory ownership and permissions.

Don’t Hide the Warning Without Fixing It

You may find instructions telling you to turn off PHP error reporting.

That can hide the message.

It doesn’t necessarily fix the problem.

There is a big difference between removing an error from view and solving the reason it exists.

For a live WordPress website, you generally don’t want visitors seeing PHP warnings anyway. But error reporting should be handled properly through your hosting and WordPress configuration rather than simply covering up an underlying fault.

The Fastest Way to Diagnose the Problem

If you’re staring at “PHP Warning: session_start(): open failed”, don’t guess.

Follow the trail.

First, read the complete error message. Identify whether it says permission denied, no such file or directory, or failed to read session data.

Then check what changed recently.

Was WordPress updated?

Did you install a plugin?

Did your hosting company migrate the website?

Did you change PHP versions?

Those clues often reveal the answer.

Final Thoughts

The “PHP Warning: session_start() open failed” message can look frightening, particularly if you’re not comfortable with PHP or server configuration.

But the cause is usually quite specific.

A missing session directory, incorrect permissions, an unsuitable session.save_path, or a plugin incorrectly handling PHP sessions are the main places to investigate.

Start with the exact error message.

Don’t randomly edit WordPress core files. Don’t give folders dangerous permissions just to make the warning disappear.

And if the problem is clearly server-related, let your hosting company deal with the server configuration.

For most WordPress users, that’s the quickest and safest route to getting the warning fixed without creating a second problem along the way.