Creating custom Ubuntu images

Roll Your Own

Article from Issue 250/2021

With a little planning, Cubic makes customizing Ubuntu ISOs simple and intuitive, saving you time on your post-install modifications.

You probably have folders full of scripts for post-install customizations for things like installing or removing packages; setting customized defaults, fonts, themes, and wallpapers; or copying files, folders, or settings from local storage. In larger organizations, these post-install customizations can include standard practices for IP address assignment, network interface specifics, network share preferences, boot config arguments, and more.

When it comes to installing the vanilla Ubuntu ISO [1] (desktop or server), your organization most likely performs these post-install customizations on dozens or even hundreds of devices, over and over again. While minor customizations based on an individual machine's or a particular machine's intended purpose are inevitable, the overarching changes to the default image are ripe for incorporating into a new custom image.

With Cubic [2], you can create a customized Ubuntu Live ISO image using Cubic's GUI wizard. Cubic takes the simplicity of a typical Ubuntu installation and combines it with all of the things that a user would normally do in the terminal or GUI post-installation. Cubic's strength lies in its ability to function as a cloning machine. With a little bit of initial planning, Cubic can you save you time when it comes to deploying machines, whether they're desktops or servers.

Why Customize?

With Cubic, the process of creating a custom Ubuntu ISO to meet your specific needs is made incredibly simple with a terminal-based app interface that should be familiar to anyone who regularly deals with the post-install blues. In fact, you can simply run those same scripts mentioned earlier to create the image itself. Then, when it comes time to execute on an upcoming deployment, you will have an all-in-one image ready to go.

While this custom image may take a bit of time to set up initially, it can save an enormous amount of time on the back end. Careful consideration on the front end to create a picture-perfect image (pun intended) can save hours of mind-numbing frustration later. In addition, you can save a fair amount of network bandwidth by having one image with all of the updates preinstalled, all the packages downloaded and included, and with nearly everything ready to go.

You may argue "sure, but I have a local network cache for my downloads so that isn't a concern." I urge you instead to consider not what you can do, but rather what can you not do if that cache is being repetitively pummeled with simple deb downloads from your internal network, while simultaneously heating up the house and sucking down the watts. Cubic offers a super easy way to work smarter and not harder, as the saying goes.

There is a downside to this convenience: Mistakes or configuration errors are then multiplied across your entire organization and network. Therefore, you must thoroughly test your installation image and ensure that it has been carefully considered. For example, opening firewall ports for one server may not be acceptable for another server with a different purpose. Again, work smarter, not harder.


Installing Cubic involves adding the PPA and using apt as follows:

$ sudo apt-add-repository ppa:cubic-wizard/release
$ sudo apt update
$ sudo apt install cubic -y

Once installed, the program can be opened from a standard desktop install's GUI.

Getting Started

First, choose the project folder, which will act as a temp folder (in non-volatile memory stored on the hard disk) for your project files until the project is complete.

Next, you need to select the original disk image file that you will customize (Figure 1). In the same dialog, you also need to assign the custom image a unique release name based on role, creation date, etc. (as specified by your organization, if applicable).

Figure 1: To get started, you must select the original Ubuntu ISO and then assign your custom image a unique release name.

After Cubic performs a quick tear-down of the original image (Figure 2), you'll be greeted with a simple chroot environment (Figure 3) where you can begin to make customizations. At this point, you can apply updates to the existing packages to create a more up-to-date image than what was originally downloaded, install and remove packages using apt, add repositories and keys, set defaults, modify schemas (remember to recompile afterwards as needed, of course), and set global user specifics. The chroot terminal is where Cubic's magic happens.

Figure 2: Cubic copies the files from the original disk image and extracts a compressed Linux filesystem.
Figure 3: Cubic's chroot terminal is where the bulk of your customizations take place.

In the chroot terminal, you can drag and drop files and folders into the Cubic window, adding them to the currently opened directory. Copy and paste also works here. If, for instance, you have a set of approved wallpapers for your organization that each user will receive, you can simply drag and drop that folder (along with its associated XML file) into the /usr/share/backgrounds folder. At login, each user then will have access to those defaults out of the box. Similarly, commonly used templates may be added to the /etc/skel directory so that each user is given the same default templates, which is especially handy for non-Office-based file formats. This step is where the bulk of the customization will take place.

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