If you are administering a Linux machine over the course of your time you will almost certainly need to get information of how much disk space is available on the drive or drives that you have mounted. This is a trivial task to accomplish however if you do not know the command you wont get far.

DF Command

The df or "disk free" command is what you need in your life! As described in the linux man pages "df displays the amount of disk space available on the file system containing each file name argument". One of the arguments it accepts is -h which lists the output in a human readable format in powers of 1024 Bytes. An example output from one of my machines is below.

$ df -h
Filesystem                         Size  Used Avail Use% Mounted on
udev                               3.9G     0  3.9G   0% /dev
tmpfs                              796M  1.2M  795M   1% /run
/dev/mapper/ubuntu--vg-ubuntu--lv   24G   12G   12G  50% /
tmpfs                              3.9G  216K  3.9G   1% /dev/shm
tmpfs                              5.0M     0  5.0M   0% /run/lock
tmpfs                              3.9G     0  3.9G   0% /sys/fs/cgroup
/dev/loop1                          56M   56M     0 100% /snap/core18/2538
/dev/loop3                          62M   62M     0 100% /snap/core20/1611
/dev/loop2                          62M   62M     0 100% /snap/core20/1593
/dev/loop4                          71M   71M     0 100% /snap/lxd/21029
/dev/loop5                          68M   68M     0 100% /snap/lxd/22753
/dev/loop6                          47M   47M     0 100% /snap/snapd/16292
/dev/loop7                          47M   47M     0 100% /snap/snapd/16010
/dev/sda2                          974M  205M  702M  23% /boot
/dev/loop8                          56M   56M     0 100% /snap/core18/2560
tmpfs                              796M     0  796M   0% /run/user/1973028261
$

As you can see it lists the filesystem, overall size, space used, space available, percentage used, and mount location.

With this output looking at the the 3rd entry in the table.

/dev/mapper/ubuntu--vg-ubuntu--lv   24G   12G   12G  50% /

I can easily tell that the root of my file system and all directories under it unless specified somewhere in this output has a total of 24G capacity and is half full. 

So as you can see this is a fairly trivial task to accomplish but you will find yourself using it all the time when forecasting and troubleshooting.