PHP: Require_once(): Unable To Allocate Memory For Pool Error and Solution

I‘m running PHP version 5.3.3 on CentOS / RHEL 6.x with APC php-pecl-apc-3.1.9. However, I’m getting the following warnings in my php server log file:

[01-Jul-2012 10:50:49] PHP Warning: require_once(): Unable to allocate memory for pool. in /var/www/html/includes/admin.php on line 57
[18-Jul-2012 17:00:08] PHP Warning: include_once(): Unable to allocate memory for pool. in //var/www/html/includes/xmlrpc.php on line 55
[18-Jul-2012 17:00:40] PHP Warning: require(): Unable to allocate memory for pool. in /var/www/html/includes/geshi.php on line 2307

How do I fix these php warnings?

This error is usually related to Alternative PHP Cache (APC). APC is a free and open opcode cache for PHP. Its goal is to provide a free, open, and robust framework for caching and optimizing PHP intermediate code.


Edit the file /etc/php.d/apc.ini (Debian and/or Ubuntu Linux user edit the /etc/php5/conf.d/apc.ini), enter:
# vi /etc/php.d/apc.ini
Make sure the mktemp-style file_mask to pass to the mmap module is correct and valid one:


Next make sure the size of each shared memory segment, with M/G suffix is set correct as per your requirements. In my case it was set to 8M:

; increased to 96M

You need to adjust the number of seconds a cache entry is allowed to idle in a slot in case this cache entry slot is needed by another entry:


The number of seconds a user cache entry is allowed to idle in a slot in case this cache entry slot is needed by another entry:


The number of seconds that a cache entry may remain on the garbage-collection list.


Save and close the file. Make sure you adjust the values as per your web-app requirements. Restart the Apache 2 web server:
# service httpd restart
If you are using the Lighttpd instead of Apache2 web-server, restart the Lighttpd web server:
# service lighttpd restart
If you are using Nginx instead of Apache2 or Lighttpd, restart the Nginx web server:
# service nginx restart
# /usr/local/nginx/sbin/nginx -s reload

Tip: Find out your APC memory usage and hit ratio

You need to find out exact memory usage and hit ratio so that you can set apc.ttl and apc.shm_size as per your work load. Copy /usr/share/php-pecl-apc/apc.php to your /var/www/html directory i.e. Apache DocumentRoot:
# cp /usr/share/php-pecl-apc/apc.php /var/www/html
Edit /var/www/html/apc.php and set the admin password :


Save and close the file. Fire a web-browser and type the url:
Sample outputs:

Fig.01: Apc Memory Status and Hit Ratio

From the above graph I’m getting 100.0% hit ratio and I’ve used almost all memory. I need to increase memory and reduce ttl value so that I will not get memory allocation error.

  1. PHP APC documentation.

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9 comments… add one
  • Daniel Oct 24, 2012 @ 7:11

    Thanks for the detailed informations. This fix worked for me.

    Greetings from Germany

  • Arindam Biswas Dec 3, 2012 @ 12:49

    Thank you. Nicely written. Your good deed of the day!


  • Igor Jan 5, 2013 @ 19:22

    Thank you for the explanation, it helped me to solve this problem.

  • Justin C. Feb 15, 2013 @ 15:03

    Worked for me! Thanks!

  • Nicram Mar 31, 2014 @ 12:02

    Great article. Today i saw same problem on my box and was trying to know what happen. It was first site and it work now. thank You!

  • rosh3000 Apr 8, 2014 @ 15:34

    Thank you. A little more explanation on how to interpreter the results in apc.php and what the graph should be like would be very useful.

  • Hưng May 26, 2015 @ 4:47

    Thank you, Unbelievable your helped!

  • robin Aug 31, 2015 @ 8:01

    Worked for me! Thanks!

  • anton Dec 28, 2015 @ 2:44

    nice explain. thanks

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