Available disk space can be queried via the command df:

$ df -h
Filesystem            Size  Used Avail Use% Mounted on
rootfs                 19G  5.9G   12G  33% /
/dev/sda1              19G  5.9G   12G  33% /
udev                   24G  216K   24G   1% /dev
tmpfs                  24G  606M   24G   3% /dev/shm
/dev/sda6             192G  188M  182G   1% /local
/dev/sda3             1.9G   95M  1.7G   6% /tmp
/dev/sda2             1.9G  879M  947M  49% /var
none                   24G  606M   24G   3% /dev/shm
master:/cm/shared     247G  125G  109G  54% /cm/shared
master:/home           17T   11T  5.8T  65% /home
fhgfs_nodev           164T  106T   58T  65% /scratch

Here the entries /home and /scratch are particularly important.