PHP flush() Function Not Working

[ddrewa]

I'm running WHM X v3.1.0 and cPanel 11.18.5 on REDHAT Enterprise 4 x86_64.

I just finished moving some scripts over from my old server and noticed that the PHP flush() function isn't working on this server. Are there any known issues with my WHM/default configuration that prevent flush() from returning input immediately? I've tried changing lots of settings in php.ini and several combinations using flush() and ob_*(), but no success.

My test script should print ten lines: one line per second. Instead, it prints all ten lines simultaneously--ten seconds from when the script is called.

[ddrewa]

Figured this out. It was being prevented by mod_security.

[jefferyw18]

where did you see mod_security? in your PHP.INI file, I am having the same issue with mine

[jefferyw18]

If flush is not working probably mod_gzip is enabled.
To disable it just add following lines to .htaccess

<IfModule mod_gzip.c>
mod_gzip_on no
</IfModule> 

[ddrewa]

mod_gzip was not running on my server, so that wasn't the problem. you can completely disable mod_security in httpd.conf or you can just disable the rule that's causing the problem (SecResponseBodyAccess) for specific files.