cron

A bunch of functions run when cron is run, to find out what is causing the overall run to take a long time (possibly timing out and breaking), you need to look at them piece by piece. This code does that:

http://drupal.org/project/drush_debug_tools

Code courtesy Tim Hilliard and tip courtesy George Cassie.

This is incorrect

Just update to the latest version. See http://data.agaric.com/raw/druplicon-feature-embedded-media-field-overlay-post for the fun story behind it.

Emfield module must be configured to have a custom directory to store its thumbnails in, otherwise the thumbnails are put in sites/default/files as temporary files (status zero), and are cleared out when cron runs.

The cron jobs for each web site are created as the user associated with that web site: the user accesses it with the crontab command

For instance:

su exampleuser
crontab -l

To see what cron jobs that user has, which should contain the "drush -r /var/local/drupal/exampleuser/web cron", where exampleuser is the site project name (which may or may not be identical to the username, but is in any case owned by the user).

The admin (root) can see them all in /var/spool/cron/crontabs

grep -h \* /var/spool/cron/crontabs/*