The df -k command displays the amount of space currently in use on each disk mounted (directly accessible) to your system. For the capacity of each disk mounted on your system, the amount of space available, and the percentage of space in use, use the df -k command.
$ df -k
If the output of the df -k command indicates your file systems are at or above 90 percent capacity, clear unnecessary files. Clear the files by moving them to a disk or tape, using cp to copy files and mv to move them, or removing files with the rm command. Perform these kinds of “housekeeping” chores only on files that you own.