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The output will look different depending on the types of disks and mount points on 
your system. In the screenshot, you'll see that the root filesystem is located on 
/dev/
mapper/ubuntu--vg-ubuntu--lv
. We know this because under the column 
Mounted on
 
we see that the mount point is set to a single forward slash (
/
). As we discussed in 
Chapter 4
, 
Navigating and Essential Commands
, this single forward slash refers to the 
beginning of the filesystem (also referred to as the root filesystem). In my case, this is 
an LVM volume, which is why we have a device with such a long name, beginning 
with 
/dev/mapper
. Let's not worry about LVM for now, we'll discuss that later. But 
for now, just keep in mind that the single forward slash refers to the beginning of the 
filesystem, and the device name on the left refers to the actual device that's mounted 
there.
The actual device name varies from one server to another, and also varies depending 
on whether you chose to utilize LVM during installation. Instead of a long path 
beginning with 
/dev/mapper
, you may instead see the device name as 
/dev/sda1
, 
/
dev/xvda1
, 
/dev/nvme0n1p1
, or other variations. The name of the device is generated 
by the type of hardware the underlying storage device is, such as the 
/dev/nvme...
 
naming convention used for NVME hard drives, 
/dev/sdaN
 for standard SATA hard 
drives, and so on.
The actual type of device the underlying hardware is doesn't matter so much; it only 
really matters that you can identify which device is at the most danger of becoming 
full. In the example screenshot, the root filesystem is using 
36%
 of its available space. 
In this case, we aren't in danger of running out of space. There are some loopback 
devices that are up to 
100%
 usage (identified by devices with a naming scheme of 
/dev/loopN
) but those aren't actually of concern, as system processes may create 
loopback devices for various purposes as needed.
While investigating disk utilization, it's also important to check inode utilization as 
well. Checking inode utilization will be especially helpful in situations where it's 
being reported that your disk is full, yet the 
df -h
 command shows plenty of free 
space is available. It can definitely be very confusing the first time you run into this 
situation. In such a scenario, it may be that you've run out of inodes, and your disk 
isn't actually full from a free space perspective.
But, what exactly is an inode, and why would such a thing cause a disk to be 
reported as full when it's actually not? Think of the concept of an inode as a type of 
database object
, containing metadata for the actual items you're storing. Information 
stored in inodes are details such as the owner of the file, permissions, last modified 
date, and type (whether it is a directory or a file). While metadata is certainly a good 
thing to have, the problem with inodes is that you can only have a limited number of 
them on any storage device. 

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Monitoring System Resources