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Serial Advanced Technology Attachment
 (
SATA
) port a hard 
disk is plugged into, which of your USB ports an external drive is connected to, and 
so on) or how you order them (in the case of virtual disks). 

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Managing Storage Volumes
[
 224 
]
Add to this the fact that removable media can be inserted or removed at any time 
and you have a situation where you don't really know what name each device is 
going to have at any one time. For example, your external hard drive may be named 
/dev/sdb1
 on your system now, but it may not be the next time you mount it if 
something else you connect claims the name of 
/dev/sdb1
. This is one situation in 
which the concept of UUIDs comes in handy. A UUID of a device will not change if 
you reorder your disks (but it will change if you reformat the volume). As stated in 
Figure 9.8
, you can easily list the UUIDs of your volumes with the 
blkid
 command:
blkid
The output will show you the UUID of each device attached to your system, and you 
can use this command any time you add new volumes to your server to list your 
UUIDs. This is also the first step in adding a new volume to your 
/etc/fstab
 file. 
While I did say that using UUIDs is not required, it's definitely recommended and 
can save you from trouble later on.
Each line of an 
fstab
 entry is broken down into several columns, each separated by 
spaces or tabs. There isn't a set number of spaces necessary to separate each column; 
in most cases, spaces are only used to line up each column to make them easier to 
read. However, at least one space is required.
In the first column of the example 
fstab
 file, we have the device identifier, which 
can be the UUID or label of each device that differentiates it from the others. (You 
can add a label to a device while formatting it with the 
-L
 argument with 
mkfs
 
commands). In the second column, we have the location we want the device to be 
mounted to. In the case of the root filesystem, this is 
/
, which (as you know) is the 
beginning of the Linux filesystem. The third entry in the screenshot (for 
swap
) has 
a mount point of 
none
, which means that a mount point is not necessary for this 
device. In the third column, we have the filesystem type, the first two being 
ext4
, and 
the third having a type of 
swap
.
In the fourth column, we have a list of options for each mount separated by a 
comma. In this case, we only have one option for each of the example lines. With the 
root filesystem, we have an option of 
errors=remount-ro
, which tells the system to 
remount the filesystem 
as read-only if an error occurs. Such an issue is rare but will 
keep your system running in read-only mode as best it can if something goes wrong. 
The 
swap
 partition has a single option of 
sw
. There are many other options that can 
be used here, so feel free to consult the man pages for a list. We will go over some of 
these options in this section.

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Chapter 9