Tag Archives: APC

PHP APC config syntax causes [apc-error] apc_mmap: mmap failed: Invalid argument

After upgrading Ubuntu server from 9.10 to 10.04LTS PHP’s APC cache wasn’t functioning.  Apache wouldn’t start, it hung in the process list and printed this error to /var/log/apache2/error.log

[apc-error] apc_mmap: mmap failed: Invalid argument

The apache process would show up in the process like this:

apc@hostaname# ps aux | grep apache
www-data 6958 104 0.0 139044 3624 ? R 12:47 0:19 /usr/sbin/apache2 -k start

This process would then have to be killed, APC commented out, and then the web server restarted just to continue on without APC until a solution was found.

The PHP manual states this regarding MMAP support in APC:


When APC is compiled with mmap support (Memory Mapping), it will use only one memory segment, unlike when APC is built with SHM (SysV Shared Memory) support that uses multiple memory segments. MMAP does not have a maximum limit like SHM does in /proc/sys/kernel/shmmax. In general MMAP support is recommeded because it will reclaim the memory faster when the webserver is restarted and all in all reduces memory allocation impact at startup.

APC was made to run by commenting out all lines from the PHP config file except for:

apc.enabled = 1

This config can exist in a number of places. In 9.10 APC had been compiled by PECL so it was in our /etc/php5/apache2/php.ini file. However, in 10.04 APC is a package so we removed the PECL version, installed the version using apt-get install php-apc and moved the configuration to /etc/php5/conf.d/apc.ini for better consistency.

pear uninstall apc
apt-get install php-apc

As I began to uncomment lines one by one, it turned out the culprit was in the apc.shm_size directive. The default size is 30M, but as soon as the directive was uncommented it crashed Apache. I was unable to specify any value at all, even the same or lesser value. I even tried with quotes and removing quotes. That’s when I started thinking syntax may be a problem because it works when using the default value (shm_size commented out) but fails with an “invalid argument” error. That makes me think APC is sending an invalid argument to MMAP. In which case I find this post that confirms my suspicion.


It turns out that the “M” for Megabytes cannot be specified in the shm_size directive for APC in Ubuntu server 10.04 because it is using APC version 3.1.3p1. However, on 9.10 APC wasn’t included as a package so it was installed with PEAR PECL which installed a more recent version of APC (3.1.9) which did allow specifying the “M” in the shm_size directive.

If you wish this to work in your config file, it should read like this in older versions of APC:

apc.shm_size = 100

This would specify 100M shared memory segments, and would be equivalent to this in newer versions:

apc.shm_size = 100M

And you can also put quotees around the “100M” if you like.

After these changes I had Apache up and running again, the APC cache helping PHP along, and some of the quickest loading pages I’ve seen in a while.

PHP’s APC cache and how it relates to Apache Bloat

You just finished your install of Apache, PHP and APC cache on a VPS and you’re beat. You spent about a day going over every configuration and compile option trying to eek performance out of your VPS machine and web server. Then you take a look at the output of top or ps and notice, hey, my Apache process is 150 Megs! Well isn’t that grand. Compiling the Big Apache on a limited resource VPS can be a challenge for those of us who like to tinker. On the last VPS I got I scrapped the packaged stuff and started on compiling an Apache for the machine. The problem is trying to meet your needs with the limited memory you usually get on these machines. Although I like lighttpd, I’m not ready to give it a go on a production server that is being monitored by the media all the time. I need something as guaranteed as I can get. Although lighttpd may be such a beast, I’m not going to test it out on this site at this time!

I sat down and started to go over all configuration option for Apache, PHP and APC to get a nice small package to do the job. I was surprised how much junk PHP has compiled in by default. Compile it once and execute a phpinfo() and you’ll see. Just start with the “–disable” switches for anything you don’t want.

After about a day of thinning out the size of my stack I slipped into TOP and used the SHIFT-A toggle to see the alternate views. I noticed something odd…..

 24140  0.1 78592  69m 7228  504 2124 2952    6    0 S  16   0    0 httpd
 11329  0.1 78408  69m 6908  504 1964 2736    2    0 S  16   0    0 httpd
 24141  0.1 78564  70m 6752  504 2120 2492    0    0 S  16   0    0 httpd
 24142  0.1 78564  70m 6732  504 2120 2476    0    0 S  16   0    0 httpd
 27813  0.1 78560  70m 6684  504 2116 2432    0    0 S  16   0    0 httpd

Doesn’t that seem like a lot of VIRT and SWAP for Apache2? Yes, it is. If you used the suggested 128 for apc.shm_size it will be a lot bigger too! I used 64M and you can see that at 78592 minus the 64M shared mem for the APC cache, the actual size is around 13M for apache with a 6.7M RES. That makes me feel better! I was so worried I had gotten something horribly wrong.

If you happen to run across this kind of thing in testing, simply set your apc.enabled in php.ini to ‘0’ to disable it, restart Apache and check ‘top’ again. Likely nothing to worry about.

The machine I am running is only hosting 4 sites so 64M is a good starting point, but what you should do is copy the file ‘apc.php’ from your APC source directory into a folder on your webserver and visit it frequently to see how it behaves. Depending on your other settings like the cache lifetime and garbage collection, if you have a large portion of FREE and a small USED then you can probably set the apc.shm_size lower. If it makes you feel better :)

PHP 5.2 and Drupal 4.7.4 don’t work together

While doing a software upgrade on a server today I ran into some problems. Apparently Drupal 4.7.4 and PHP 5.2.1 don’t work together.

After upgrading PHP, Apache and APC cache I couldn’t get Drupal to work on all 7 sites on one machine. I could login to any drupal site as the admin and get shown my user page, but when trying to do anything at all as an authenticated user it considered me logged out.

I initially thought APC had something to do with it and began to disable it. That didn’t fix it. On a haunch and after a lot of reading with no answer I decided to install a lesser version of PHP and that fixed it. PHP 5.1.1 was laying around and did the trick. Unfortunately I needed 5.2 to fix a mem leak!

I decided to update the Drupal sites to the latest version first to see if that helps. Lo and behold when I visit the Drupal download page I am greeted with:

PHP 5.2 compatibility is only available from Drupal 4.6.11 / 4.7.5 / 5.x.

That pretty much cinches it. I need PHP 5.2 to fix a memory leak so I’ll take time to upgrade to Drupal 5 now.

Be warned, if you are running Drupal 4.7.4 sites and attempt to upgrade to PHP 5.2 you may be faced with being unable to login or navigate as an authenticated user in Drupal. Downgrade to PHP 5.1, upgrade to > Drupal 4.7.4 and then continue your upgrade to PHP 5.2 and you should be alright.