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Here, let's say that I have an external disk that I only mount when I'm performing 
a backup. I wouldn't want this device mounted automatically at boot time (I may 
not always have it connected to the server), so I use the 
noauto
 option. But since I 
do have an entry for it in 
/etc/fstab
, I can easily mount it any time after I connect it 
with the following command:
sudo mount /mnt/ext_disk
Notice that I didn't have to include the device name or options; only the destination 
path for the mount. The 
mount
 command knows what device I'm referring to since 
I have an entry in the 
/etc/fstab
 file for a device to be mounted at 
/mnt/ext_disk
. 
This saves me from having to type the device name and options each time I want to 
mount the device. So, in addition to mounting devices at boot time, the 
/etc/fstab
 
file also becomes a convenient place to declare devices that may be used on an on-
demand basis but aren't always attached.
One final option I would like to cover before we move on is 
users
. When used with 
a mount in 
/etc/fstab
, this allows regular users (users other than 
root
) to mount 
and unmount the filesystem. This way, 
root
 or 
sudo
 will not be necessary at all for 
a mount used with this option. Use this with care, but it can be useful if you have 
a device with non-critical data you don't mind your users having full control over 
when mounting and unmounting.
While the 
concept of a text file controlling which devices are mounted on the 
system may seem odd at first, I think you'll appreciate being able to view a single 
file in order to find out everything that should be mounted and where it should be 
mounted. As long as administrators add all on-demand devices to this file, it can be 
a convenient place to get an overview of the filesystems that are in use on the server. 
As a bonus, you can also use the 
mount
 command (with no options) to have the 
system provide you with a list of everything that's mounted. Go ahead and try that, 
and I'll meet you in the next section.