[cobalt-users] / is full and / is what? where?

[M Smart <cobalt@xxxxxxxxxxxxxxxxxx>]

Got an e-mail from our automated admin account today.

Labled: 

Subject: The filesystem [/] is getting very full

is getting very close to full.  This is very dangerous for the server
and can cause unexpected errors to occur.  You either need to move some
files to another storage device and delete them from the Cobalt server
or delete them altogether.  Consult the documentation for help adding
storage to your Cobalt server.

Total disk space:  725.95 MB
Free disk space:  49.99 MB
Percent Used:  93 %

I can't locate the / file. I'm the owner of the box and it just so happens my
actual admin guy is on holiday this week.  Can some one point me to
documentation on this or out and out answer me as to where I find this
source. 
Generally we get an e-mail indicating a v-host is a violator. What / is, is a
mystery to me.

Thanks
Humble Owner
Jake