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.