Linux Filesystems 101 - Block Devices

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Creating a partition

Recall that the sda device has an extra 600 MiB of unused space on it after the sda1 partition. Let's make use of this extra space by creating a new partition on the device. First, we should take a quick look at the partition table. To do so, type the command:

sudo fdisk -l /dev/sda

NOTE: The sudo at the beginning of the command causes the command to be executed with the super user (root) account. Try running the fdisk command without sudo. What happens? The /dev/sda file is crucial for system operation. It holds the enitre operating system. It would be a severe security risk if a non-privleged account could access this file.

Start the VM

The output of fdisk looks like this:

Disk /dev/sda: 2 GiB, 2147483648 bytes, 4194304 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x8c44efc8

Device     Boot Start     End Sectors  Size Id Type
/dev/sda1        2048 2936012 2933965  1.4G 83 Linux

This gives us some new information about our sda disk. It confirms that it is, indeed, a 2 GiB device, and it tells us that it is comprised of 4,194,304 sectors, each of which is 512 bytes (0.5 KiB) in size. It also tells us that the first partition, /dev/sda1 is 2,933,965 sectors in size, from sector 2,048 to sector 2,936,012.

Let's try creating a new partition after this one. Type sudo fdisk /dev/sda. This will start up the fdisk utility, and provides you with a prompt for a command.

Type p and press Enter. The p command prints out the partition table. This is the information we already saw.

Type n and press Enter. This will create a new partition. You will be prompted for several pieces of information (partition type, number, etc.) For now, just press Enter for each prompt to accept the default values. Eventually you will see the following message:

Created a new partition 2 of type 'Linux' and of size 614 MiB.

To see your new partition, use the p command again to print the partition table. The partition you just created is listed as /dev/sda2. When you are done admiring your handiwork, type w (for write) and press Enter. This will exit the fdisk utility.

NOTE: The fdisk utility reads and writes MBR-style partition tables. This is an older technology that is slowly being phased out and replaced with the GPT partitioning scheme. We'll discuss this in more detail in another course (link TBD). For now, let's stick with MBR.

Before exiting, fdisk informs you that the new partition isn't visible to the OS yet. You can verify this with lsblk. Let's make it visible. Execute the following command:

sudo partprobe /dev/sda

Now execute lsblk. Do you see the new partition?

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