Setting up tablepace

Hi all,
I have a problem with setting up tablespace on a ramdisk.
the ramdisk shall be used temporary for storing unprotected map data, that is normaly protected.

I'm working in Linux.
I have an ordirnary Linux user called normaluser, a user called chartuser (the ramdisk owner, the password is not known
tothe normal users), and a ordinary postgres user. 

Chartuser and root are the only ones that has access to the ramdisk.

I have succeeded to store (as normaluser) the unprotected map files on the ramdisk, only accessable for chartuser.

I would now like to import the map files to a GIS db that has the tabespace on the ramdisk. But I'm not able to create
thetablespace on the ramdisk. 
Trying logged in as chartuser to run: psql -c "CREATE TABLESPACE ramspc LOCATION '/tmp/ramdisk0/tblspace'"
 "could not set permission on directory "/tmp/ramdisk0/tblspace": premission denied"...

Any ideas, anyone?
Thanks,
Paul