How to check hard drive capacity in linux

as a network admin of course we are required to know about the state of the server, not least about how much hard disk capacity is already in use by the system and for data storage.

Especially if the server is a storage server, then how much hard drive capacity is used absolutely must know.

Here are the commands associated with these needs:

udiniq@blackstone:~/Desktop$ df

Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1             52888108   5124808  45076736  11% /
udev                    242304         4    242300   1% /dev
tmpfs                    99728       788     98940   1% /run
none                      5120         0      5120   0% /run/lock
none                    249316       144    249172   1% /run/shm

if you want to display in units of hard disk capacity, then the command

udiniq@blackstone:~/Desktop$ df -h

Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1              51G  4.9G   43G  11% /
udev                  237M  4.0K  237M   1% /dev
tmpfs                  98M  788K   97M   1% /run
none                  5.0M     0  5.0M   0% /run/lock
none                  244M  144K  244M   1% /run/shm