How to find disk free space / disk usage ?

'df' - finding the disk free space / disk usage

$ df

It gives a table consisting of 6 columns.

Remember that the 'Size', 'Used' and 'Avail' columns use kilobytes as the unit.

The 'Use%' column shows the usage as a percentage which is also very useful.

$ df -h

Displays the same output as the previous command but the '-h' indicates human readable format.

Hence instead of kilobytes as the unit the output would have 'M' for Megabytes and 'G' for Gigabytes.

$ df -h | grep /dev/hda1 | cut -c 41-43

Example of Answer

45%

Basically this command makes 'df' display the disk usages of all the partitions and then extracts the lines with /dev/hda1.

Then it cuts the characters from the 41st to the 43rd column since they are the columns that display the usage in %.