Installing Enterprise Linux 7 in a VirtualBox virtual machine isn't difficult, but there are a few items necessary for the rest of this course. In this video, learn how to create a VM, install CentOS 7 in it, and go over the most important options in detail.
- For this course we'll be installing CentOS 7 Enterprise Linux. To install from full DVD we need to download an ISO image from the CentOS website. We'll do this by opening a web browser, and browsing to the CentOS download site at, CentOS.org/download. Click "DVD ISO", and choose a server near you. Then, click on "Save File", and click "OK". If you don't know where any of these are just randomly select one. Now that our CentOS image is downloaded, we can install it. To install CentOS 7 in a virtual machine, we need to have VirtualBox running and then click on "New".
Lets name the virtual machine "CentOS7 Full DVD". (typing sound) Then, click on "Next". Now we'll set the memory to 1.5 gigabytes or more, if you have it. Keep in mind, we'll be running two virtual machines simultaneously in this course. So you want to use less than half the available RAM for each. In my case, the dialogue box shows I have 16 gigabytes of free RAM; so I could give each VM up to eight gigabytes if I wanted to, but that's not necessary.
I'm going to set my RAM to 1.5 gigabytes, and click "Next". The next dialogue is for the Virtual Disk. Click "Create". Then, click on "Next" to accept the Virtual Disk type, and click "Next" again to accept dynamically allocated. This saves space by not allocating all of the disk space up front. We can now choose the size of the disk. The default is eight gigabytes. There's nothing wrong with selecting a larger size than the default, if you have the extra space available. But you can always add a second virtual box drive later if you need it.
So it's okay to just take the defaults here. Click on "Create". Now select the VM named "CentOS7 Full DVD", and click on "Start". Click the folder icon to select the CentOS 7 ISO image. Then, click on "Open", and then click on "Start". On the boot screen highlight, "Install CentOS7" with the cursor keys, and press "Enter". You could choose a second option to test install media as well. This is mainly for ISO images that have been burned to physical disc.
This will test to see if the disc is not corrupt. We don't usually have to do this for ISO images that reside on the hard drive. To make installing easier, go to full screen mode by pressing "Host key + F". In my case, the host key is the right control key, which I can see in the bottom right hand corner of my VM window. As such, I will press "Right Control F". In the first dialogue choose the install language. This is just the language used during installation, and click on "Continue".
We now see the installation summary screen where we will configure how OS is installed. Click on the date and time and choose your time zone, and then click on "Done". Next, we'll click on "Software Selection". These are installation configurations which go from a very bare install, without a GUI, to full fledge desktop work stations. The default is "Minimal Install". We're going to choose the "Server with GUI". This configuration does include a ton of packages, but still has a full graphical interface. Don't get too worried about installing software here, as it can all be done later.
Now click on "Done". The next thing we'll do is click on "Installation Destination". Make sure the "ATA VBOX HARDDISK" is selected. If you choose "Automatically configure partitions", the installer sets up three partitions automatically. There's nothing wrong with this choice, as a default partition layout is pretty good. If you choose, "I will configure partitions", you can set-up partitions manually. Using this option you still have a link for the installer to create the partitions for you. The advantage to choosing "I will configure partitions", is that you get to see the default partition layout and modify those results if you wish.
Let's click "I will configure partitions" now. You may also notice that at the bottom of the screen, there's a check box labeled, "Encrypt my data", if you are installing on a mobile device such as a laptop, I recommend turning encryption on. By default, CentOS 7 uses the AES algorithm to encrypt. If you have a recent intel CPU with AES-ni instruction built in, there will be very little performance degradation when turning on disk encryption. For this course, we'll leave it turned off. Now click on "Done".
This brings us to the Manual Partitioning screen. Click on the link titled, "Click here to create them automatically". Clicking this link brings up a new screen showing the proposed partition layout. The installer wants to create a small partition accessible as "/boot", where our Linux cURL and other boot files are stored, using the xfs file system. Second, it wants to create a much larger root partition where the rest of the OS is stored, also using the xfs file system. It also wants to create a smaller swap partition to use for virtual memory.
We can add any of these configuration details in the screen. Let's just click "Done" and "Accept Changes" to accept installer suggestions. We don't need the network configure to install with a full DVD, but if you wanted to configure the network now you could. We'll do it later. Click on "Begin Installation". While the install proceeds, we'll give the root user a password and set-up an admin user. Click on "Root Password". You want a very strong password here for the root user because in Linux the root user is all-powerful, and the username is known to hackers making it a target.
If a hacker were to get this password, they'd have access to the entire system. The installer tells you if your password strength is good or not. Use a combination of numbers, letters that are both uppercase and lowercase, and symbols for your strong password. The installer will let you proceed with a weak password if you wish, by clicking "Done" twice. However, it's not recommended. Now let's click on "Done". If the installer doesn't let you go on, then the two passwords probably don't match. It doesn't give you a lot of indication of this, but if you look at the bottom of the screen, you'll see the message.
You don't ever want to login as Root and especially not on the GUI. The Root user has too much power, and there are too few safeguards. So on Linux, we create a regular user. Click on "User Creation". Here is where we'd enter our name into the full name box, and it will create a lowercase version of it for our username. Lets use the name "user 1" for this course. You can always add a user with you name later if you wish. We will also set a password in the screen. We'll create a strong password here as well, because we're going to make this first user an administrator by clicking on the checkbox labeled, "Make this user an administrator".
It is very important that you click this box now, as the rest of our course depends on it. If you fail to click this box, you'll need to login as Root after the install is finished, and add this user manually to the wheel group. It's best to do it now. We'll also want to give this user a strong password since we're giving him them admin privileges. (typing sound) Then, click on "Done. The install will take between 20 minutes to an hour depending on your host computer's hardware. As soon as the install is finished, you will be able to click on "Reboot" to reboot into your new CentOS 7 VM.
As soon as the system reboots, we want to click on "License Information", click on "I accept license agreement" and click on "Done". And then click on "Finish Configuration". Now login as the user you created. Notice that Root isn't even given as an option in the GUI. You can specify any user if you click on the "Not listed" link, however, I really don't recommend logging in as Root. (typing sound) As soon as you login you'll be prompted to choose your language.
I'll choose a default which CentOS gets from the installer, and click on "Next". I will also choose a default for the keyboard. Click on "Next" again, and click on "Skip creating online accounts". Then, click on "Start using CentOS Linux". As soon as we're logged in, CentOS displays a "Getting Started" window explaining how the CentOS desktop works. For now, let's close this window. Virtual Box allows us to do things that wouldn't be possible with a physical computer, such as snapshots. We can snapshot our VMs so we never have to install again.
If anything goes wrong, and we want to revert to a fresh installation, we can. To snapshot our new VM press the "host key plus T". Let's call this first snapshot, "Fresh Install". (typing sound) Then click on "OK". To shut down your CentOS VM properly, select the top right menu in the title bar, and click the power button. This will let you restart or shut down your VM, but we're not going to do it quite yet.
Click on "Cancel". If you want to revert back to the previous snap shot, go out of full screen mode by pressing "host plus F". And then click on the close gadget to close the VM window. You will be presented with three options: Save the machine state, Send the shutdown signal, or Power off the machine. Selecting "Send the shutdown signal" is the nice way to Shut down an OS, and is basically doing the same thing as selecting the shut down option from within CentOS. Selecting "Power off", just pulls the virtual power cord.
Linux is pretty good at handling this sort of thing, but there still may be disk-corruption, so I don't recommend it. However, if we went to revert to the previous snapshot, we're not concerned about the current state of the disk, since it's snapshoted. Select "Power off the machine" and then click on "Restore current snapshot 'Fresh Install'" and click on "OK". Your VM will now be reverted back to the previous snapshot, which currently is the fresh install.
- Gathering network information
- Ensuring connectivity with ping
- Querying DNS servers with dig
- Changing hostname, IP address, and more
- Configuring networking
- Connecting to SSH
- Configuring SSH clients
- Authenticating and restricting access with SSH
- Optimizing SSH for speed