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If you are a WordPress user, you are bound to encounter specific errors that can halt your work. One of the common errors users is the 503 error service not available. The HTTP error 503 may appear in different operating systems, including Windows XP, Linux, macOS, etc.

What's the HTTP 503 Service Unavailable Error?

The 503 service unavailable in WordPress indicates that your website is now inaccessible due to the server in question being unavailable. It might be due to a high volume of traffic, maintenance, or anything else that necessitates a more thorough analysis.

The error message usually comes in various forms like-

503 Service Temporarily Unavailable

HTTP Server Error 503

Error 503 Fetch Backend Failed

Websites which uses Microsoft IIS usually adds a digit after 503 error giving away more details about the reason behind this server error.

Fix 503 Service Unavailable Error

 The service error is from the server end, which means the issue is coming from the webite server. It's conceivable that a problem with your computer causes the HTTP 503 error, but this is unlikely. In other words, the status code 503 (Service Unavailable) indicates that the server is presently unable to process the request owing to temporary server maintenance, which will most likely be resolved within some time.

Some of the ways to resolve the 503 Error Service Unavailable are:

Temporarily Deactivate Your WordPress Plugins:

Plugin difficulties are one of the major reasons for the error 503 in WordPress. The best is to disable WordPress plugins to see the exact reason behind the issue.

You can also use the FTP client since the 503 error prohibits you from accessing the WordPress admin area. You need to connect website using your FTP client once it's ready, and check the root folder of WordPress. It's generally named public_html, public, www, or your site's name.

Restarting your Router and Modem

Restarting your modem or router is yet another way to overcome this error. While the 503 error is almost always the fault of the website you're viewing, it's conceivable that there's a problem with your network or computer's DNS server setup, which a quick restart of both could fix. If rebooting your device did not resolve the 503 DNS Failure, the DNS servers themselves may be experiencing temporary difficulties. In this situation, update your DNS servers on your computer or router using our list of Free & Public DNS Servers.

Calling out Experts

Another alternative is to get assistance directly from the website backend team. There's a high probability that the site administrators are already aware of the 503 error, but informing them or checking on the progress of the problem is a smart idea.

Disabling Content Delivery Network (CDN)

The 503 error may appear due to an issue with your Content Delivery Network rather than a problem with your website. Whether you're utilizing a CDN, temporarily turning it off might help you figure out if this is the case.

Depending on the type of CDN you are using, you must take may change. Cloud flare sometimes also leads to 503 errors. If you cannot halt yours, try the knowledge base for your service, including extensive instructions.

Connect with Experts

Here are some very simple ways of fixing 502 Bad Gateway errors from the client side.

Reload the page

The first thing you should do is reload the page and wait for a minute. If the 502 Bad Gateway error disappears, it means there was a temporary problem with the upstream server or the networking between servers. If the error remains, check if the site is down for everyone. You can use Is it down right now? for this. If the site is up for everyone except you, open the site on another browser or in private mode.

Clear browser cache

Another easy tip is to clear the browser cache. If the error disappears after cleaning cache, it means that there was a temporary problem that has been resolved, but because of cache, you kept seeing the 502 Bad Gateway error template, instead of your website. If the error remains, try the next tip.

Flush DNS cache

The 502 Bad Gateway error can occur because of DNS issues. Operating systems, such as Linux, Windows, and macOS save name resolution information in the form of a DNS cache. In many cases clearing the DNS cache can solve a 502 Bad Gateway error. Here are the commands which you can use for flushing DNS cache on Windows, MacOs, and Linux. Use this command to flush cache on Windows:

ipconfig /flushdns

On macOS, you should open the terminal and type:

sudo killall -HUP mDNSResponder

There’s no message after processing this command, but you can add your own by running the command like this:

sudo killall -HUP mDNSResponder; dns cleared successfully

Things are different in Linux, as different Linux distributions use different DNS services. Some of them are NSCD (Name Service Caching Daemon), dnsmasq, and BIND (Berkeley Internet Name Domain). For an NSCD DNS cache:

sudo /etc/init.d/nscd restart

For a dnsmasq DNS cache:

sudo /etc/init.d/dnsmasq restart

For a BIND DNS cache:

sudo /etc/init.d/named restart

sudo rndc restart

sudo rndc

exec

If the terminal asks for your password, just enter it.

Change DNS servers

You can also try to temporarily change your DNS servers. More information about changing DNS servers can be found in this article: Change your DNS servers settings.

If you’re using Cloudflare

Cloudflare returns a Cloudflare-branded HTTP 502 error when your origin web server responds with a standard HTTP 502 bad gateway: This means that something is wrong with your origin server and you can try to use the above-described tips to fix the issue. If the 502 error is from Cloudflare, the page looks like this: If the error contains the word “Cloudflare,” the problem comes from Cloudflare, otherwise, it is from the origin server. In the first case, you can contact Cloudflare support, and in the second case, you can follow the described tips. If nothing helps, contact your hosting provider. You can read more about Cloudflare 5xx errors in the article Troubleshooting Cloudflare 5XX errors.

We’ve discussed some client-side tips which can help you troubleshoot a 502 Bad Gateway error. Now let’s see what you can do on the server-side.

Restart PHP

The very first step is to restart your PHP. With 10Web, you can do this by going to Hosting Services > Tools and clicking the blue “Restart PHP” button. If your hosting doesn’t provide an interface for restarting PHP, ask them to do it for you.

Check logs

Checking your server error logs can give you very useful information about 502 Bad Gateway errors. With 10Web, you can easily check server logs by going to Hosting Services > Logs. If you have access to your file system, you can check server logs. In the case of the Nginx web server, you can find logs here:

/

var

/log/nginx

In the case of Apache web server, the logs are in this repository:

/

var

/log/apache2

Improper firewall configuration

Improper firewall configuration can lead to 502 Bad Gateway errors. A firewall is a network security system that monitors and controls the incoming and outgoing network traffic based on predetermined security rules. It typically establishes a barrier between a trusted network and an untrusted network. There can be cases that some awkward firewall settings can consider safe and valid content malicious and, consequently, cut off traffic which in turn cause 502 Bad Gateway errors. Check your firewall configuration to reveal any improper configs.

Third-party plugins & themes

Non-optimal codes in WordPress plugins and themes can also cause 502 errors. So, check your plugins and theme. If you have access to your WordPress admin, deactivate all your plugins, and if the error disappears it means that there is at least one guilty plugin. Then activate them one by one to find the guilty ones. If your WordPress admin area can’t be reached because of the error but you have access to your WordPress files, just rename the plugins directory in wp-content. It will deactivate all plugins. And again start activating them one by one.

If the problem isn’t the plugins, that is deactivating all plugins or renaming plugins directory doesn’t change anything, try to temporarily change your theme to WordPress’s default theme. Once you find the bad plugins or theme, connect to the respective support team and describe the issue. And don’t forget to keep your plugins, theme, and WordPress core up-to-date. This will help you avoid many problems, including 502 errors.

Restart PHP-FPM service

You will get a 502 error if the PHP-FPM service is inactive or not running on your server. If you have access to your hosting, you can check this by running one of the following commands. For SysVinit:

sudo service php7.4-fpm status

For SystemD:

sudo systemctl status php7.4-fpm

If the service is active and running, the output of the command should be like this: If the status is not Active: active(running), try restarting PHP-FPM service to resolve the error using one of the following commands. For SysVinit:

sudo service php7.4-fpm restart

For SystemD:

sudo systemctl restart php7.4-fpm

Timeout issues

The 502 error can be caused by a PHP-FPM timeout. If your application is taking too long to respond, your users will experience a timeout error. If the PHP-FPM timeout is less than Nginx timeout, Nginx will return a 502 Bad Gateway error. To avoid this, you can increase PHP-FPM timeout if you have access to your server.

PHP-FPM timeout is set in pool configuration which is

request_terminate_timeout

The default value for this directive is 20 seconds. If you don’t have access to your server, ask your hosting provider to check it. To avoid getting 504 errors after increasing PHP-FPM timeout which can be because of Nginx timeout, the default is 60 seconds, you can increase fastcgi_read_timeout directive in /etc/nginx/nginx.conf file. Don’t forget to reload the Nginx server after changing the directive:

nginx -s reload

PHP execution time errors can also lead to 502 Bad Gateway errors. To avoid this, you can increase the PHP configs, such as max_exexution_time and max_input_time.

What is a Syntax Error?

A syntax error occurs when there’s a mistake in your code. As a result, the compiler cannot process (parse) the file and fail to display your website.

On WordPress, syntax errors are usually caused by incorrect lines in PHP scripts. Some common mistakes are incorrect coding structure, missing punctuations, invalid variables, and wrong function names.

What are Parse Errors?

In the context of PHP, parsing is what happens when your code is being converted from a series of characters to the final result that visitors are going to see on your site.

These errors occur when the PHP code can’t start or finish being parsed for one reason or another. It could be that the file or database is missing, corrupt or broken, your version of PHP isn’t compatible with WordPress, your file permissions aren’t set correctly, your server ran out of PHP memory or there’s a structural error in the code.

In WordPress, the latter is typically what you may come across the most and there are three main kinds:

Syntax error – There are problems with the semicolons, or curly brackets or quotations that were used. Either their missing or the wrong ones were included.

Unexpected error – You forgot to include a character such as an opening or closing bracket or other possible characters.

Undefined constant error – A character is missing in an array, when referencing a variable or other possible scenarios.

Keep in mind that these three kinds of parsing errors have many different variations depending on the specific mistake in the code. Read on for more details on this and how to fix these errors.

Fixing Parse Errors

Parse errors may seem terrifying, but they’re one of the simpler errors to resolve. Somewhere in the code you just added, there’s a character missing or out of place and if you open the offending file and correct it, the error goes away.

If you just added code yourself or you installed a plugin or theme before the error occurred, that’s where you need to look to fix the issue. Removing the code, plugin or theme should resolve the issue or you can go ahead and fix it yourself.

There’s a great way to narrow down where the cause of the error lies since the full error codes give you a great hint of where to look.

Below are the basic structures of the full parse error codes mentioned above that you’re most likely going to come across.

Syntax errors have this basic structure:

“Parse error: syntax error, unexpected character in path/to/php-file.php on line number“

Undefined constant errors are structured this way:

“Notice: Use of undefined constant constant string – assumed ‘constant string‘ in path/to/php-file.php on line number“

Unexpected errors can have different variations, but generally look like the example below:

“Parse error: unexpected character in path/to/php-file.php on line number“

Keep in mind that for undefined constant errors, the named constant string may not actually be a string since PHP often refers to unidentified tokens as constant strings.

Similarly, unexpected parse errors may list a string instead of a character.

In each of these examples, number refers to the line number and is going to be replaced with actual numbers such as 23 or 1256, for example, though, not necessarily those exact line numbers.

The file indicated in the error message is where the issue persists and the line number gives you a hint as to where to look for the mistake. It’s either on that line or a little bit before it.

The character or constant string names in these structure examples give you an idea of what to look for around the indicated line number. These are what needs fixing or else they’re related to what needs correcting.

Now that you know where and what to look for, you can log into your site using your preferred FTP client to locate the file and either edit it directly in your FTP client or you can download it to your computer, edit it, then re-upload it back to your site.

For details on using FTP, check out one of our other posts How to Use FTP Properly with WordPress.

Avoiding these Errors

Avoiding these errors is as easy as fixing them if you’re at least a little familiar with PHP. You can check your code for syntax mistakes automatically by running it through a PHP code validator.

Here are some free validators you can use:

W3 Markup Validation Service

PHP Code Checker

PHP code Syntax Check

Here are some tips of the most common syntax mistakes to look out for right off the bat:

Make sure there’s only one opening (<?php) and closing tag (?>)per document

Look for opening and closing tags in the middle of a file

If you add code, be sure it’s included before a closing tag and not after it

Add code shouldn’t be inserted in between a function

Check for functions that are broken up by other ones

For details on PHP syntax, check out these resources:

Basic PHP Syntax

PHP Tags

Escaping from HTML

Instruction Separation

Comments

The 401 (Unauthorized) status code indicates that the request has not been applied because it lacks valid authentication credentials for the target resource. The server generating a 401 response MUST send a WWW-Authenticate header field containing at least one challenge applicable to the target resource. 

How to Fix the 401 Error?

Now that we’ve gone through a bit of background on the 401 error, it’s time to discuss how you can resolve it.

Let’s take a look at five methods you can use:

Look for Errors in the URL

Clear Your Browser’s Cache

Flush Your DNS

Deactivate Your WordPress Plugins

Check the WWW-Authenticate Header Response

1. Look for Errors in the URL

We’ll start off with the easiest potential fix: making sure you used the correct URL. This may sound simple, but 401 errors can sometimes appear if the URL wasn’t correctly entered in.

Another possibility is that the link you used to visit the page in question points to the wrong URL. For example, it might be outdated, or leading to a page that no longer exists (and no redirects are in place).

Therefore, it’s worth double-checking the URL you used. If you typed it in yourself, verify that you spelled everything correctly. If you clicked on a link, confirm that it’s pointing to the page you’re trying to access (or try to visit that page directly through the website).

2. Clear Your Browser’s Cache

Your browser’s cache is designed to improve your online experience, by reducing page loading times. Unfortunately, sometimes it can also cause unwanted interruptions.

As we mentioned earlier, one of the common causes of the 401 error is outdated or incorrect cache data or cookies. Therefore, if you don’t notice any issues with the page’s URL, the next step is to clear your browser’s cache.

This will clean out any invalid information that’s locally stored in your browser, which could be interrupting the authentication process. Similarly, your browser’s cookies might contain authentication data that simply needs to be refreshed.

If you’re a Google Chrome user, you can do this by clicking on the menu icon in the top-right corner of the browser, and then going to Settings. Under the Privacy and security section, click on Clear browsing data:

A new window will open. Under the Basic tab, make sure all three boxes are selected, and then select Clear data:

This process will look a little different in other browsers. For example, in Mozilla Firefox, you would click on the library icon in the top-right corner of the browser, followed by History > Clear Recent History:

In the panel that opens next, select Everything in the drop-down menu at the top, make sure “Cache” is selected, and then click on the Clear Now button:

If you’re using a different browser, please refer to this guide for clearing the cache

3. Flush Your DNS

Another method you can try to resolve the 401 error is flushing your Domain Name Server (DNS). While this is a rarer issue, it can be a possible cause, so it’s worth giving it a try if the first two solutions don’t work.

To do this in Windows, click on the Start button and type cmd into the search bar. Hit Enter, and the Command Prompt will open. Copy and paste the command ipconfig/flushdns, and then hit Enter again:

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On a Mac, you can do this by going to Finder > Applications > Utilities > Terminal:

Input the command line sudo killall -HUP mDNSResponder and press Enter. Then, you can try refreshing the page you were trying to visit, to see if the 401 error has been resolved.

4. Deactivate Your WordPress Plugins

The problem causing your 401 error might not be due to your browser. If you’re having trouble accessing your WordPress site, it’s also possible that one or more plugins are to blame.

Some plugins, especially security-focused plugins, are configured to show a 401 error when they suspect suspicious login activity that might indicate an attack. Others might just be suffering from compatibility issues. Therefore, it’s a good idea to deactivate all of your WordPress plugins and see if that resolves the issue.

You can deactivate your plugins all at the same time in your dashboard, by going to Plugins > Installed Plugins. Check the box at the top to select all of them. Then under the Bulk Actions drop-down menu, select Deactivate and click on the Apply button:

After that, try reloading the page that returned the 401 error to see if this has resolved the issue. If it has, you can manually activate each plugin one at a time, in order to determine which one is causing the problem.

Then you can remove that plugin, replace it with a new one, or contact its developer for assistance.

5. Check the WWW-Authenticate Header Response

At this point, if the issue hasn’t been fixed, it may be caused by a server-side problem. This means our last fix will be a bit more involved.

As we saw earlier, the 401 response is sent through the WWW-Authenticate header, which appears as “WWW-Authenticate: <type> realm=<realm>”. It includes ‘challenges’, or strings of data that indicate what type of authentication is required in order for access to be granted.

In a nutshell, you’ll want to check and see if the header response was sent, and more specifically, what authentication scheme was used. At the very least, this can help narrow down the cause of the problem, and bring you one step closer to a solution.

To do this, go to the web page that’s displaying the 401 error, and access the developer console in Chrome. You can right-click on the page and select Inspect, or use Ctrl+Shift+J.

Next, click on the Network tab and reload the page. This will generate a list of resources. Select the Status header to sort the table and locate the 401 status code:

Select that entry, and then click on the Headers tab. Under Response Headers, locate the WWW-Authenticate header:

The information that is present in the response header, particularly the authentication schemes, can give you more information about what’s happening and point you towards a solution. It can help you understand what type of authentication the server is expecting.

A  503 Service Unavailable Error  is an HTTP response status code indicating that a server is temporarily unable to handle the request. This may be due to the server being overloaded or down for maintenance. This particular response code differs from a code like the 500 Internal Server Error we explored some time ago. While a 500 Internal Server Error indicates an issue preventing the server from handling the request entirely, a 503 Service Unavailable Error is an indication that the server is still functioning properly, since it’s able to process the request and has opted to return the 503 response code.

As with most HTTP response codes that indicate an error like this, it can be difficult to determine the exact cause of a 503 Service Unavailable. There are dozens of possible HTTP status codes used to represent the complex relationship between the client, a web application, a web server, and often multiple third-party web services, so determining the cause of a particular status code can be a challenge, even under the best of circumstances. In this article we’ll examine the 503 Service Unavailable by looking at a few troubleshooting tips, along with some potential fixes for common problems that might be causing this issue, so let’s get started!

The Problem is Server-Side

All HTTP response status codes that are in the 5xx category are considered server error responses. Unlike the 502 Bad Gateway Error we’ve looked at recently, which indicates that a server somewhere in the connection chain is down or unavailable, a 503 Service Unavailable Error simply indicates that the server is temporarily unable to handle the request, but that is is functioning as normal otherwise. Unlike gateway related 5xx response codes that may indicate issues either on the web server or another server further upstream, the 503 Service Unavailable code generally indicates an issue on the actual web server hosting your application.

In most cases, the web server should provide a user-friendly page indicating that the service is temporarily unavailable. Additionally, the application should send a Response-After HTTP header, which informs the user agent (client) how long it should wait to attempt the request once again. This value should either be a Date value indicating the timestamp the service will be available, or a numeric value indicating how many seconds from now the user agent must wait to retry.

Since the 503 Service Unavailable indicates that something has gone wrong within the server of your application, we can largely disregard the client side of things. If you’re trying to diagnose an issue with your own application, you can immediately ignore most client-side code and components, such as HTML, cascading style sheets (CSS), client-side JavaScript, and so forth. This doesn’t apply solely to web sites, either. Many smart phone apps that have a modern looking user interface are actually powered by a normal web application behind the scenes; one that is simply hidden from the user. If you’re using such an application and a 503 Service Unavailable Error occurs, the issue isn’t going to be related to the app installed on your phone or local testing device. Instead, it will be something on the server-side, which is performing most of the logic and processing behind the scenes, outside the purview of the local interface presented to the user.

Start With a Thorough Application Backup

As with anything, it’s better to have played it safe at the start than to screw something up and come to regret it later on down the road. As such, it is critical that you perform a full backup of your application, database, and so forth, before attempting any fixes or changes to the system. Even better, if you have the capability, create a complete copy of the application onto a secondary staging server that isn’t “live,” or isn’t otherwise active and available to the public. This will give you a clean testing ground with which to test all potential fixes to resolve the issue, without threatening the security or sanctity of your live application.

Diagnosing a 503 Service Unavailable Error

As mentioned, a 503 Service Unavailable Error indicates that the server (typically the actual web server on which your application is running) is temporarily unavailable. This is usually due to the server being “down” for scheduled maintenance, or due to a heavy load of traffic that is preventing it from properly serving all incoming requests. In the case of the former, the server has not actually crashed or shut down but has, instead, set itself to a mode of service that prevents most requests from behaving as normal. Thus, attempting to access a normally-functional page now displays a 503 Service Unavailable Error, ideally doing so alongside a message about the server being down for maintenance. In this mode, the server is still up and running, but only administrators will have access to it, whereas normal public requests will be turned away until maintenance is complete.

In the other scenario where the server is rejecting the request due to overload, this usually means there is an unexpected onslaught of traffic/incoming requests. In order to maintain some semblance of normal behavior for a portion of the requests, the server has effectively throttled itself by rejecting a portion of all incoming requests and returning a 503 Service Unavailable Error. If the application/server was configured correctly, the request can usually be completed by waiting a little while and retrying a few times, hopefully enough for the traffic spike to die down and let you in.

That said, if your application is responding with 503 Service Unavailable codes and the server should not be performing any kind of maintenance that would explain the situation, this is an issue that many other visitors could be experiencing as well, dramatically hindering your application’s ability to service users. We’ll go over some troubleshooting tips and tricks to help you try to resolve this issue. If nothing here works, don’t forget that Google is your friend. Don’t be afraid to search for specific terms related to your issue, such as the name of your application’s CMS or web server software, along with 503 Service Unavailable Error. Chances are you’ll find others who have experienced this issue and have been given a solution.

Troubleshooting on the Server-Side

Here are some additional tips to help you troubleshoot what might be causing the 503 Service Unavailable to appear on the server-side of things:

Reboot the Server – If you or an administrator have the ability to do so, one of the simplest solutions is often to restart the web server hosting the application. If your application is spread over multiple servers, make sure all are rebooted in the proper manner so the system is brought back online as normal. A 503 Service Unavailable code could be a result of a bottleneck somewhere in the server chain that hosts your application, so a simple reboot could refresh everything and get you back up and running.

Check for Unexpected Maintenance – You may not realize it, but your server and/or application may be configured to go down for maintenance automatically. Many modern content management systems like WordPress will automatically download and install updates to their base software without any intervention on your behalf. The web server could be issuing 503 Service Unavailable Errors during this period, particularly if your application resides on a slower server or a shared host. If you’re able to access the administration settings of your application/server, check the configuration options for automatic maintenance scheduling or the like, disabling such options if you’d rather have direct control over that process (just don’t forget to upgrade to newer versions fairly regularly, as they typically include critical security fixes).

Server Connectivity Issues – While it may sound simple, it’s entirely possible that a 503 Service Unavailable Error simply indicates that a server somewhere in the chain is down or unreachable for whatever reason. Most modern applications don’t reside on a single server, but may, instead, be spread over multiple systems, or even rely on many third-party services to function. If any one of these servers are down for maintenance or otherwise inaccessible, this could result in an error that appears to be from your own application.

Improper Firewall Configuration – A firewall is a basic security device that monitors network traffic and acts as a gatekeeper, deciding which traffic is safe and which could be malicious. In most cases, all potentially harmful traffic is stopped (and may be logged for network admin use). In some situations, it’s entirely possible for a firewall configured somewhere on the network in which your application is running to be preventing some form of critical traffic from getting through. This is particularly true for applications that rely on content delivery networks (CDNs), which act as a third-party host for “heavy” content like images or videos, hosting that content on behalf of your application, so your application can maintain its speed and efficiency. However, automatic firewall services can sometimes perform false positives, mistaking perfectly safe and valid content from CDNs or elsewhere as malicious, thereby shutting off that stream of content in an instant, which could lead to a 503 Service Unavailable Error.

Check the Logs – Nearly every web application will keep some form of server-side logs. Application logs are typically the history of what the application did, such as which pages were requested, which servers it connected to, which database results it provides, and so forth. Server logs are related to the actual hardware that is running the application, and will often provide details about the health and status of all connected services, or even just the server itself. Google “logs [PLATFORM_NAME]” if you’re using a CMS, or “logs [PROGRAMMING_LANGUAGE]” and “logs [OPERATING_SYSTEM]” if you’re running a custom application, to get more information on finding the logs in question.

Application Code or Script Bugs – If all else fails, it may be that a problem in some custom code within your application is causing the issue. Try to diagnose where the issue may be coming from through manually debugging your application, along with parsing through application and server logs. Ideally, make a copy of the entire application to a local development machine and perform a step-by-step debug process, which will allow you to recreate the exact scenario in which the 503 Service Unavailable Error occurred and view the application code at the moment something goes wrong.