Linux Basics for Hackers

Summary

Linux has a number of commands to enable you to combine and compress your files for easier transfer. For combining files, tar is the command of choice, and you have at least three utilities for compressing files—gzip, bzip2, and compress—all with different compression ratios. The dd command goes above and beyond. It enables you to make a physical copy of storage devices without the logical structures such as a filesystem, allowing you to recover such artifacts as deleted files.
EXERCISES
Before you move on to Chapter 10, try out the skills you learned from this chapter by completing the following exercises:

1. 
   Create three scripts to combine, similar to what we did in Chapter 8. Name them Linux4Hackers1, Linux4Hackers2, and Linux4Hackers3.
   
2. 
   Create a tarball from these three files. Name the tarball L4H. Note how the size of the sum of the three files changes when they are tarred together.
   
3. 
   Compress the L4H tarball with gzip. Note how the size of the file changes. Investigate how you can control overwriting existing files. Now uncompress the L4H file.
   
4. 
   Repeat Exercise 3 using both bzip2 and compress.
   
5. 
   Make a physical, bit-by-bit copy of one of your flash drives using the dd command.
   

10
FILESYSTEM AND STORAGE DEVICE
MANAGEMENT

If you are coming from a Windows environment, the way that Linux represents and manages storage devices will look rather different to you. You’ve already seen that the filesystem has no physical representation of the drive, like the C:, D:, or E: system in Windows, but rather has a file tree structure with / at the top, or root, of it. This chapter takes a look at how Linux represents storage devices such as hard drives, flash drives, and other storage devices.
We first look how additional drives and other storage devices are mounted upon that filesystem, leading up to the / (root) directory. Mounting in this context simply means attaching drives or disks to the filesystem to make them accessible to the operating system (OS). For you as a hacker, it’s necessary to understand the file and storage device management system, both on your own system and, often, the system of your target. Hackers commonly use external media to load data, hacking tools, or even their OS. Once you’re on your target system, you need to understand what you’re working with, where to find confidential or other critical files, how to mount a drive to the target, and whether and where you can put those files on your system. We cover all of these topics, plus how to manage and monitor storage devices, in this chapter.
We begin with the directory known as /dev, which you’ve probably already noticed in the directory structure: dev is short for device, and every device in Linux is represented by its own file within the /dev directory. Let’s start out by working with /dev.