URGENT: Whole DB down ("no space left on device")

I am getting this message when I start the DB:


psql: FATAL:  could not access status of transaction 0
DETAIL:  Could not write to file "pg_subtrans/01F8" at offset 221184:
No space left on device.


What is this about and how do I solve this? A "df -h" on my system shows this:


Filesystem    Type    Size  Used Avail Use% Mounted on
/dev/sda5     ext3    9.9G  2.5G  6.9G  27% /
/dev/sda1     ext3     99M   17M   78M  18% /boot
none         tmpfs    2.0G     0  2.0G   0% /dev/shm
/dev/sda7     ext3    197G   17G  171G   9% /home
/dev/sda8     ext3   1012M   34M  927M   4% /tmp
/dev/sda3     ext3    9.9G  4.4G  5.0G  47% /usr
/dev/sda2     ext3    9.9G  9.5G     0 100% /var
/tmp          none   1012M   34M  927M   4% /var/tmp


Please help!