Internal Error 500 Apache, but nothing in the logs?

I'm getting 500 Internal Server errors when I try to make an HTTP POST to a specific address in my app. I've looked into the server logs in the custom log directory specified in the virtual hosts file, but the error doesn't show up there so debugging this has been a pain in the ass.

How do I cause Apache to log Internal 500 errors into the error log?

Why are the 500 Internal Server Errors not being logged into your apache error logs?

The errors that cause your 500 Internal Server Error are coming from a PHP module. By default, PHP does NOT log these errors. Reason being you want web requests go as fast as physically possible and it's a security hazard to log errors to screen where attackers can observe them.

These instructions to enable Internal Server Error Logging are for Ubuntu 12.10 with PHP 5.3.10 and Apache/2.2.22.

Make sure PHP logging is turned on:

1. Locate your php.ini file:

   el@apollo:~$ locate php.ini
   /etc/php5/apache2/php.ini
   

2. Edit that file as root:

   sudo vi /etc/php5/apache2/php.ini
   

3. Find this line in php.ini:

   display_errors = Off
   

4. Change the above line to this:

   display_errors = On
   

5. Lower down in the file you'll see this:

   ;display_startup_errors
   ;   Default Value: Off
   ;   Development Value: On
   ;   Production Value: Off
   
   ;error_reporting
   ;   Default Value: E_ALL & ~E_NOTICE
   ;   Development Value: E_ALL | E_STRICT
   ;   Production Value: E_ALL & ~E_DEPRECATED
   

6. The semicolons are comments, that means the lines don't take effect. Change those lines so they look like this:

   display_startup_errors = On
   ;   Default Value: Off
   ;   Development Value: On
   ;   Production Value: Off
   
   error_reporting = E_ALL
   ;   Default Value: E_ALL & ~E_NOTICE
   ;   Development Value: E_ALL | E_STRICT
   ;   Production Value: E_ALL & ~E_DEPRECATED
   

   What this communicates to PHP is that we want to log all these errors. Warning, there will be a large performance hit, so you don't want this enabled on production because logging takes work and work takes time, time costs money.

7. Restarting PHP and Apache should apply the change.

8. Do what you did to cause the 500 Internal Server error again, and check the log:

   tail -f /var/log/apache2/error.log
   

9. You should see the 500 error at the end, something like this:

   [Wed Dec 11 01:00:40 2013] [error] [client 192.168.11.11] PHP Fatal error:  
   Call to undefined function Foobar\\byob\\penguin\\alert() in /yourproject/
   your_src/symfony/Controller/MessedUpController.php on line 249
   

Check your php error log which might be a separate file from your apache error log.

Find it by going to phpinfo() and check for error_log attribute. If it is not set. Set it: https://stackoverflow.com/a/12835262/445131

Maybe your post_max_size is too small for what you're trying to post, or one of the other max memory settings is too low.

I just ran into this and it was due to a mod_authnz_ldap misconfiguration in my .htaccess file. Absolutely nothing was being logged, but I kept getting a 500 error.

If you run into this particular issue, you can change the log level of mod_authnz_ldap like so:

LogLevel warn authnz_ldap_module:debug

That will use a log level of debug for mod_authnz_ldap but warn for everything else (https://httpd.apache.org/docs/2.4/en/mod/core.html#loglevel).

If your Internal Server Error information doesn't show up in log files, you probably need to restart the Apache service.

I've found that Apache 2.4 (at least on Windows platform) tends to stubbornly refuse to flush log files—instead, logged data remains in memory for quite a while. It's a good idea from the performance point of view but it can be confusing when developing.

The answers by @eric-leschinski is correct.

But there is another case if your Server API is FPM/FastCGI (Default on Centos 8 or you can check use phpinfo() function)

In this case:

1. Run phpinfo() in a php file;
2. Looking for Loaded Configuration File param to see where is config file for your PHP.
3. Edit config file like @eric-leschinski 's answer.
4. Check Server API param. If your server only use apache handle API -> restart apache. If your server use php-fpm you must restart php-fpm service > systemctl restart php-fpm

Check the log file in php-fpm log folder. eg /var/log/php-fpm/www-error.log

Please Note: The original poster was not specifically asking about PHP. All the php centric answers make large assumptions not relevant to the actual question.

The default error log as opposed to the scripts error logs usually has the (more) specific error. often it will be permissions denied or even an interpreter that can't be found.

This means the fault almost always lies with your script. e.g you uploaded a perl script but didnt give it execute permissions? or perhaps it was corrupted in a linux environment if you write the script in windows and then upload it to the server without the line endings being converted you will get this error.

in perl if you forget

print "content-type: text/html\r\n\r\n";

you will get this error

There are many reasons for it. so please first check your error log and then provide some more information.

The default error log is often in /var/log/httpd/error_log or /var/log/apache2/error.log.

The reason you look at the default error logs (as indicated above) is because errors don't always get posted into the custom error log as defined in the virtual host.

Assumes linux and not necessarily perl

Please check if you are disable error reporting somewhere in your code.

There was a place in my code where I have disabled it, so I added the debug code after it:

require_once("inc/req.php");   <-- Error reporting is disabled here

// overwrite it
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

Add HttpProtocolOptions Unsafe to your apache config file and restart the apache server. It shows the error details.

In my case it was the ErrorLog directive in httpd.conf. Just accidently noticed it already after I gave up. Decided to share the discovery ) Now I know where to find the 500-errors.

Check that the version of php you're running matches your codebase. For example, your local environment may be running php 5.4 (and things run fine) and maybe you're testing your code on a new machine that has php 5.3 installed. If you are using 5.4 syntax such as [] for array() then you'll get the situation you described above.

Try accessing a static file. If this is not working either then go to all directories from the root "/" or "c:" to the directory of your file and check if they contain ".htaccess" files.

I once left a file in "c:" and it had the most strange results.