Unix fundamentals - mount points

  • April 13, 2007
  • Avatar for peter

Today, I'm going to introduce the concept of mount points. Mount points are, in essence, folders in which external filesystems are mounted (their contents are dropped into that folder). We'll be going into that in a bit more detail in just a second. First of all, the obligatory Wikipedia definition:

A mount point is a term used to describe where the computer puts the files in a file system on Unix-like systems. For example, many modern Linux distributions automatically mount the CD drive as /mnt/cdrom, so the contents of the CD drive will appear in the /mnt/cdrom directory. A device can be mounted anywhere on the directory structure. Normally only the root user can mount a new file system but systems are often configured so that users may mount pre-set devices. A file system can be mounted by running the mount utility.

Windows, OS/2 and other operating systems that have their heritage in DOS and the old days of the IBM PC, use a drive letter structure to access different devices on the system. I'm sure you're aware of the idea of the C drive under Windows.

Well, Unix-like operating systems don't work anything like that, I'm afraid.

Let's have a quick example. I've got a 512 MB USB stick and I plug it into my PC running Linux. Behind the scenes, the operating system does the following:

  • Creates a folder called /media/PETER512 (PETER512 is the volume name of my USB stick).
  • Mounts the USB stick's contents inside this new folder

Fairly simple. So what does it actually do when it mounts the contents? Think of it as taking the contents of the device and dropping them into that folder. Now, if you browse to that folder, you can read and write the contents of the actual device, just as if it was a normal folder on your hard drive.

The folder (which is the mount point - the point where that device is mounted) can be anywhere, but it's a convention that you use /media or /mnt. Equally, it doesn't have to be a USB stick. CDs, DVDs, network drives, removable hard drives, even .iso image files, can be mounted so you can access them and interact with them.

And finally, a quick command line practical exercise. You will need to know the device string of whatever you want to mount, which unfortunately makes this process a bit geeky and difficult. In this example, I'm using /dev/sda1 (which is what most USB devices are if you have IDE hard drive).

In most cases, you also need administrator/root privileges to mount and unmount.

# mkdir /mnt/mymountpoint
# mount /dev/sda1 /mnt/mymountpoint

When you're done, you can unmount the device with umount (optionally, you could also rmdir the folder if you don't need it).

# umount /mnt/mymountpoint

Avatar for peter Peter Upfold

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