Description
IO Device Files
Structure
The exercise is broken into these main parts:
- Create a storage device image file.
- Connect the file to a loopback device, format it, and mount a filesystem on the device.
- Write data to the virtual device by creating files on it after mounting
- Unmount the virtual device and disconnect the loopback device 5) Verify the data has been written to the image file
Creating the Image
Follow these steps to completed the exercise:
- Create a img file, filled with zeroes, of size one megabyte (1MiB) using dd:
$ dd if=<input file> of=<output file> bs=<block size> count=<how many>
The dd command’s input can come from any source, a regular file or a special (device) file. A special file, /dev/zero, will have an infinite number of zeroes available for reading. The output data’s size is defined by the block-size and block-count – you could create a 1KiB file by using a size of 512 and a count of 2, for example.
- Create a loopback device connected to the image file via losetup, format the image in ext4 format using mkfs, and then mount the loopback device on /mnt/ex6 via mount. Take a screenshot of the commands you used in this step.
- You will need to use sudo for the losetup
- In this step you will be writing data to the virtual device by creating files on it after mounting.
In the mounted directory (/mnt/ex6), create two text files:
- one empty,
- and one containing a message.
Display the contents of each file using the cat command and take a screenshot.
- Unmount the filesystem (umount) and disconnect the loopback device (losetup).
- Lastly, you need to verify if the data has been written to the image file.
Install the hexedit program (sudo apt-get install hexedit) and use it to examine the image file – you should be able to find your filenames and text. Take a screenshot.
Just for fun: try the strings command and see what happens!
