KaOS Linux is an unusual case in the world of Linux distributions. First, because it is not derived from any other distribution; second, because it is so tightly focused on the KDE desktop; and third, because it is a rolling distribution. When you put those three things together, it makes it interesting enough for me to keep KaOS Linux loaded on one or two of my laptops.
The KaOS developers recently announced the availability of a new stable ISO image. Because KaOS is a rolling distribution, it is not necessary to reinstall an existing system when a new image is released; simply making sure that you keep up with the official updates is sufficient. But it is good form (and polite) to release a fresh ISO image periodically so that new systems don't have to be loaded with a relatively old image and then have a large number of updates to install.
I find it interesting that other larger and better known distributions struggle to provide this small courtesy, or just don't even bother to try any more (I'm looking at you PCLinuxOS and LMDE), while this little KaOS distribution manages to produce an updated ISO every two months. Kudos to the KaOS developers for that.
The focus of KaOS exclusively on KDE is also interesting, and admirable. It seems like these days most of the Linux distributions just keep adding more and more "spins", or "community distributions", or some other way of adding more desktops. Perhaps we should start a scoreboard, and track how many different "supported" desktops each distribution has. I can think of several which would be around 10 or so.
The KDE-centric nature of the distribution includes not only the desktop, but all of the utilities, applications and packages included in the distribution. It uses the QupZilla browser, not Firefox or Chrome (although it also include Konqueror); Calligra for office applications rather than LibreOffice or OpenOffice, and much more.
Those who want to add their favorite non-KDE applications can usually do so directly from the KaOS repositories. I just checked and found firefox, google-chrome, libreoffice and vlc all available for installation in the octopi software manager.
According to the release announcement, the new version supports UEFI boot (using systemd-boot), but not Secure Boot. My experience so far has confirmed that, but I have run into a couple of quirks in this area, detailed below.
The ISO image can be obtained from the KaOS Download page, where there is also a link to the MD5 checksum. I couldn't find any information about GPG signing or other validation of either the downloaded image or the checksum value.
The ISO image is in hybrid format, so you can dd it directly to a USB stick or burn it to a DVD - at 1.7GB it is far too large for a CD. It can then be booted on either MBR or UEFI systems, but note that as mentioned above, on UEFI firmware you must disable Secure Boot first.
Installation is fairly straightforward. When the Live image is booted, a 'Welcome to KaOS' window is automatically displayed. Clicking the Install KaOS button (top left) starts the Calamares Installer - but be prepared to wait a bit, because it takes a long time to start.
I have written about Calamares in detail before, so I will not go through it step-by-step here. The one place that you have to be careful is in the disk partitioning, because KaOS wants the EFI Boot partition to mount on /boot, rather than /boot/efi like most other distributions. I suppose this is actually a characteristic of the systemd-boot package, but I have looked at that in detail yet.
Once installed, KaOS boots to a typical KDE Plasma 5 desktop.
I was disappointed to find that digiKam is not included in the base installation, but then I was very pleasantly surprised when I installed it using octopi, and saw that it was version 5.0 Beta! This is the first distribution I have seen which includes that. Oh, and I was also pleased to see that this release includes the new spectacle screen-shot utility rather than the older Ksnapshot.
The biggest surprise came, though, when I tried to reset the EFI boot sequence so that my laptop would boot openSuSE by default. I found that the efibootmgr program is not included in the base distribution. I can't quite get my head around that one, it must be a mistake or an oversight of some sort.
I then went to octopi (Add/Remove Software), expecting to simply install efibootmgr, and was even more surprised to find that it is not even listed there!? In fact, none of the EFI support packages is listed, so this really must be some kind of packaging mistake or oversight.
In summary I would say that if KDE Plasma 5 is your cup of tea, then KaOS could be worth your careful consideration. I have found it to be clean, simple and solid (despite the minor annoyance of the missing efibootmgr). Furthermore, if you are happy with only the KDE applications and utilities, it is ready to go out of the box, but if you want you can add some of the more popular general-use applications such as Firefox, LibreOffice, VLC and such, they are available in the KaOS Add/Remove Software utility.
As I frequently say when people ask me about these smaller distributions, when in doubt, give it a try. It doesn't take much time or effort to create and boot the Live media, and then see what you think.