Magento – Log Cleaning does not work

Under System -> Configuration -> System you'll find a setting which dictates the frequency of the cron schedule generation. When the cron schedule is generated, the time stamp is stored in a cache record outside the scope of any defined cache tags, meaning it is not gotten rid of unless the storage is flushed vs flushing the tagged cache records. The time stamp in this cache record is checked on each run to determine if enough time has elapsed for a schedule generation to run.

So in short: it's working as intended. :)

The reason the cron schedule is not calculated on each execution cycle is for performance reasons. It's far less computationally expensive to dump a precalculated schedule into the cron_schedule table and execute based on what is is found in there on each run. This same table is consequently also used for placing a lock on each job.

If you are needing to refresh the conversion rates manually, you can do it from the currency rates management page on the click of a button. If you are just wanting to effect a change in the timing of the refresh, change the setting and check back later, it will be picked up the next time the cron schedule is generated prior to the set time. Or just flush the cache storage to see it take effect immediately... ;)

It was the PHP version of Cron Jobs.

The PHP version was set correctly for the site which is why it was working; however Cron Jobs was running at server native PHP 5.3 which is why I was getting the errors only when running Cron. I updated to version 5.5.

Changed Cron command:

php /home/mydomainname/public_html/cron.php
to
php55 /home/mydomainname/public_html/cron.php

or in hostgator:

/opt/php55/bin/php /home/mydomainname/public_html/cron.php

in cron.php

$isShellDisabled = (stripos(PHP_OS, 'win') === false) ? $isShellDisabled : true;

After this line, add:

$isShellDisabled = true;