temporary file location?

At the end of a long query that I am running I got the following error:

ERROR:  ltsWriteBlock: failed to write block 2427094 of temporary file
        Perhaps out of disk space?


my df -h looks like this:

Filesystem            Size  Used Avail Use% Mounted on
/dev/sda6             372M  215M  138M  61% /
/dev/sda1              45M   16M   27M  36% /boot
/dev/sda3             8.5G  811M  7.2G  10% /home
none                  250M     0  250M   0% /dev/shm
/dev/sda2              23G  3.6G   18G  16% /usr
/dev/sda7             251M  142M   96M  60% /var


Yes, these are the default redhat partitions. Where is postgresql
writing temporary tables to? Is that a configurable parameter?
Thanks.