I want to create customized usb live .iso based on ubuntu-16.04.1-server-amd64.iso. I've seen this guide for desktop edition, but for some reason /casper directory is missing in server installation image. There is another article customizing from scratch, but it requires Host system to be installed first. Is there any way to create ubuntu-server live image without installing it?
We are creating a live server for 18.04 LTS that will enable simpler installation in the common cases, but also be generally useful for everyday testing. See http://cdimage.ubuntu.com/ubuntu-server/daily-live/current/ for the current build, bugs and comments welcome.
There is no true "Live" option on Server editions (they don't have a "Try Ubuntu" option in boot menu). I think they are built only with installations in mind.
Also usually most Linux default liveCD/DVD editions refer only to their desktop variants. See this answer.
To achieve your goal i'll suggest making the LiveCD from scartch (not starting from existing LiveCD) following the instructions you already linked.
To do this, you need a linux host (it's a base and inevitable requirement). If you can't install on a true PC, i'll suggest doing it inside a virtual machine (maybe with VirtualBox o you preferred hypervisor) to make the LiveCD iso from there.
Hope it helps.
Please tell us how you intend to use your customized Ubuntu Server, and we can help you find what you need or at least help you along the way! (It is not easy to create an own iso file. You are basically asking how to create an own linux distro based on Ubuntu Server.)
For example, would this work for you: A basic text screen installed system, that boots in UEFI and BIOS mode and is quite portable between computers? I know that it is not exactly what you are asking for, but maybe the easiest way to get what you need. It is very easy to install to a USB pendrive from a compressed image file. See this link
We can suggest other and maybe better alternatives, when we know how you intend to use your customized operating system :-)
As posted above by Mark Shuttleworth (http://cdimage.ubuntu.com/ubuntu-server/daily-live/current/). You can use the image there to make a live usb.
This was a little more complicated than I was hoping, however, the end result works very well. I first attempted to create a live usb via a VM, installing directly to the USB from the bionic installer, however, it appears that it did not partition the drive correctly and would not boot.
Failing that, I created a virtual hdd for my vm, installed the bionic live server to that, and then created an image out of the virtual hdd. Once that was complete it was a simple matter of using
dd to move the image onto my usb.