In my servers Apache error log I regularly see the entry:

mod_fcgid: stderr: PHP Fatal error: Call to undefined function module_list() in /home/example/public_html/includes/bootstrap.inc on line 1074

Lines 1066 -> 1078 in bootstrap.inc are:

function bootstrap_invoke_all($hook) {
  // Bootstrap modules should have been loaded when this function is called, so
  // we don't need to tell module_list() to reset its internal list (and we
  // therefore leave the first parameter at its default value of FALSE). We
  // still pass in TRUE for the second parameter, though; in case this is the
  // first time during the bootstrap that module_list() is called, we want to
  // make sure that its internal cache is primed with the bootstrap modules
  // only.
  foreach (module_list(FALSE, TRUE) as $module) {
    drupal_load('module', $module);
    module_invoke($module, $hook);

No errors appear in Drupal's Database logging. Today I have received some white screen 503s when checking the site and each time a new message appears in the Apache log. I have tried clearing caches and running drush cc all.

Does anyone has a suggestion as to what is causing this error or how to resolve it?

Some specifications about my set-up: PHP 5.5.12 (OPcache 7.0.4 as bundled), MariaDB 5.5.37, Apache HTTP 2.2.15, Centos 6.5 and Drupal 7.28. OPcache is 'Up and Running'.

To check if OPcache was the causing the problem I disabled it and monitored the error log. The error message still appears with OPcache disabled, and as it disabling it slows the site site significantly (in the region of 200ms > 600 ms) I have re-enabled.

  • APC/other opcode cache problem maybe? – Clive May 24 '14 at 16:21
  • Thanks for the suggestion Clive, I have been looking into OPcache. I cannot find any bugs that produce similar errors which have not already been fixed in the current version. I have added specifications to my question in case this is the cause of the problem. – Taylor Taff May 25 '14 at 9:47
  • May be worth testing with an earlier PHP version as well, as 5.3 is recommended for D7 ( drupal.org/requirements ) – David Thomas May 25 '14 at 11:58
  • As far as I can tell one of the main differences which causes issues between PHP 5.3 & 5.4+ is that OPcache is present. I am currently testing with OPcache disabled to see if it caused the error previously. I will let that test run for a while and if no change will swap down to PHP 5.3. – Taylor Taff May 25 '14 at 16:20
  • The error still occurs with OPcache disabled so I do not think it is the cause of the problem. – Taylor Taff May 26 '14 at 10:37

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