df -h

Show disk space usage for all mounted filesystems

df -h (disk free, human-readable) shows every mounted filesystem with size, used, available, and use%. Use% over 90% needs immediate attention. Check df -h before every long-running task.

Example

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        20G   18G  1.2G  94% /

Tip: Type it yourself in the terminal below - reading is not the same as doing.