A virtual machine is an emulation of a physical machine. This means it runs inside a physical machine, as opposed to directly on the hardware. A physical machine has direct access to all hardware, such as the CPU, the RAM, and other devices such as the mouse, the keyboard, and the monitor. It is, however, impossible to share the CPU or the RAM between multiple physical machines. Virtual machines do not directly get access to hardware, but through an emulation layer, which means resources can be shared between multiple virtual machines.

Because we're discussing Bash shell scripting in general, in theory it does not matter what kind of an installation is performed. As long as that installation runs a compatible Linux operating system with Bash 4.4 or later, all exercises should work. There are, however, many advantages to using a virtual machine over a physical installation:

• There is no need to remove your current preferred operating system, or set up a complicated dual-boot configuration
• Virtual machines can be snapshotted, which allows recovery from critical failures
• You are able to run (many) different operating systems on a single machine

Unfortunately, there are also drawbacks associated with virtual machine use:

• Because you're running a virtual operating system within an already running operating system, there is some overhead from the virtualization (in comparison to running a bare-metal installation)
• Since you're running multiple operating systems at the same time, you will need more resources than with a bare-metal installation

In our opinion, modern computers are fast enough to make the drawbacks almost trivial, while the advantages provided by running Linux in a virtual machine are very helpful. Because of this, we will only be explaining a virtual machine setup in the rest of this chapter. If you feel confident enough to run Linux as a physical installation (or perhaps you already have Linux running somewhere!), feel free to explore the rest of the book with that machine.

If you want to be sure all examples and exercises work as seen in this book, run an Ubuntu 18.04 LTS virtual machine in VirtualBox with the recommended specifications of 1 CPU, 1 GB RAM, and a 10 GB hard disk: this setup is described in the rest of this chapter. Even if many other types of deployment should work, you would not want to be banging your head against the wall for hours when an exercise is not working, before discovering it was caused by your setup.