[gentoo-user] Postgres gem not found by cron job

[Michael Orlitzky <michael@orlitzky.com>]

I feel like I should be able to solve this one, but it started after my 
last world update so maybe someone else has had a similar problem.

We have a ruby script called 'mailshears' on our mail server that cleans 
up orphaned users and domains every night. The main script,

   /root/src/mailshears/bin/mailshears

includes a class,

   require 'src/postfixadmin_db'

which in turn requires the postgres library from ruby-postgres:

   require 'postgres'

I don't think there's anything fancy going on here. All of the required 
packages are installed, and the script runs fine when I execute it 
manually. For example, both of the following work:

   cd /root/src/mailshears/bin/
   ./mailshears

   cd /
   export PATH=/sbin:/bin:/usr/sbin:/usr/bin
   export HOME=/
   /root/src/mailshears/bin/mailshears

(That last one mimics my crontab.) The problem is, whenever the nightly 
cron job runs, the 'postgres' library can't be found. I get mailed this 
every night:

   /root/src/mailshears/bin/../src/postfixadmin_db.rb:1:in `require': no
   such file to load -- postgres (LoadError)
	from /root/src/mailshears/bin/../src/postfixadmin_db.rb:1
	from /etc/cron.daily/01mailshears:35:in `require'
	from /etc/cron.daily/01mailshears:35

The path /etc/cron.daily/01mailshears is simply a symlink to 
/root/src/mailshears/bin/mailshears, and of course, if I execute that 
symlink manually, it runs fine.

What's different between my root environment and the one in which cron 
runs (with respect to ruby and its gems)? Where should I start looking?