How to free the space in /dev/sda9

It says bash: cannot create temp file for here-document: No space left on device

Following the space distribution:

 Filesystem      Size  Used Avail Use% Mounted on  udev            3.9G     0  3.9G   0% /dev  tmpfs           787M  9.8M  777M   2% /run  /dev/sda9        19G   18G  8.0K 100% /  tmpfs           3.9G  172K  3.9G   1% /dev/shm  tmpfs           5.0M  4.0K  5.0M   1% /run/lock  tmpfs           3.9G     0  3.9G   0% /sys/fs/cgroup  cgmfs           100K     0  100K   0% /run/cgmanager/fs  tmpfs           787M   36K  787M   1% /run/user/1000 

How to resolve it ?