documentation for file owner and permission.

this is both a support request and a task, feel free to change if appropriate:

I have a VPS that happens to have cpanel. if I run drush dl as the root, everything works as expected. however, if I run drush dl as one of the cpanel users, I get the following message:

"WD php: file_put_contents(/tmp/cache.inc): failed to open stream: [error]
Permission denied in /drush/commands/pm/pm.drush.inc on line 2419.
file_put_contents(/tmp/cache.inc): failed to open stream: Permission [warning]
denied in /drush/commands/pm/pm.drush.inc on line 2419."

the project is downloaded fine afterwards, but I know that there's something wrong in setting up drush or the permissions /owner. I have installed in /drush and made an alias for it as in the documentation.

I see a need to write some instructions about this in the documentation. help, anybody?