Ocasional error warning when CakePHP is writing to the cache - cakephp

Question

I'm developing a CakePHP 2.2 site locally with MAMP. Every so often, I get one or more warnings similar to this, about not being able to write to one or more cache files:
Warning: SplFileInfo::openFile(/Applications/MAMP/htdocs/mywebsite/www/app/tmp/cache/persistent/myapp_cake_core_cake_console_en-au): failed to open stream: Permission denied in /Applications/MAMP/htdocs/mywebsite/www/lib/Cake/Cache/Engine/FileEngine.php on line 313
The weird thing is, /tmp is 777, tmp/cache is 777, and tmp/cache/persistent is 777 (don't worry... it won't be 777 on the server!). The file itself inside tmp/cache/persistent is 644 - but I assume Cake is creating and managing that file, and does so with the permissions it needs.
If I just refresh the page, the error goes away (and then re-appears sometime later). I'm not doing any explicit caching, so this stuff is just Cake doing whatever it automatically does.
So my question is:
a) How does this automatic caching of Cake's work? Is it trying to write to that file on every page refresh, and failing only once in a while? Or is it only trying to write to that file once in a while, but failing every time it tries?
b) If it's only failing only once in a while, can I safely just ignore it? And if it's failing every time it tries, how can I fix it?
Thanks in advance for any help!

Answer 1

This happens probably when a process different from Apache create files in the cache. This can be the case for instance when you run shell commands as you probably do it as a different user than apache.
By default the File cache creates files with permissions allowing only the user that has created the files to modify them, but this can be fixed by setting a mask in the Cache config in core.php:
Cache::config('_cake_core_', array(
'engine' => $engine,
'prefix' => 'cake_core_',
'path' => CACHE . 'persistent' . DS,
'serialize' => ($engine === 'File'),
'duration' => $duration,
'mask' => 0666
));
Cache::config('_cake_model_', array(
'engine' => $engine,
'prefix' => 'cake_model_',
'path' => CACHE . 'models' . DS,
'serialize' => ($engine === 'File'),
'duration' => $duration,
'mask' => 0666
));

Answer 2

If you want to avoid giving read/write access to the "other" group, check out my other solution here:
https://stackoverflow.com/a/18703956/385979

Answer 3

Simple really, assuming and you are a sudoer and your user name is martinlutherking
sudo adduser martinlutherking www-data
This way cake console commands can read cache files created by apache2, however you may need to do the inverse group add to ensure that www-data can read cache files created by martinlutherking

Answer 4

Just in case anybody is seeing this and wonders how it works in cakePHP 3.x:
modify /config/app.php and add 'mask' => 0666 to
/**
* Configure the cache adapters.
*/
'Cache' => [
'default' => [
'className' => 'File',
'path' => CACHE,
'url' => env('CACHE_DEFAULT_URL', null),
'mask' => 0666
],
and probably you also want to add it to the log files:
/**
* Configures logging options
*/
'Log' => [
'debug' => [
'className' => 'Cake\Log\Engine\FileLog',
'path' => LOGS,
'file' => 'debug',
'levels' => ['notice', 'info', 'debug'],
'url' => env('LOG_DEBUG_URL', null),
'mask' => 0666
],
'error' => [
'className' => 'Cake\Log\Engine\FileLog',
'path' => LOGS,
'file' => 'error',
'levels' => ['warning', 'error', 'critical', 'alert', 'emergency'],
'url' => env('LOG_ERROR_URL', null),
'mask' => 0666
],
],