Ubuntu 12.04: How to check free disk space?

Sometimes we urgently need to figure out the free disk space and the following commands are handy to use:

Command 1

df

this command gives information about various directories on the system. The values are shown in 1K block which are quite hard to understand. Therefore following command is better.

Command 2

df -h

this command will produce the output in GB (gigabytes), MB (megabytes) and KB (kilobytes) which is very easy to read and understand.

Please share what other commands do you use to find free disk space on the server.