These instructions (https://www.ubuntu.com/download/desktop/create-a-usb-stick-on-ubuntu) doesn't work for Ubuntu Server iso. Doing
dd if=ubuntuserver.iso of=/dev/sdb doesn't work either. In both situations, after the Ubuntu Server installer boots correctly, it says it hasn't found any CD drive and stops.
I've a USB stick where I've put the content of Ubuntu Server iso on it. I've configured Syslinux (with no APPEND parameter) pointing to vmlinuz+initrd present in "install" folder. The installer boots correctly but it hangs with an error saying it doesn't find the CD-ROM.
If I replace the vmlinuz+initrd with the "hd-media" ones (available here) I get another error: installer can't find any iso file anywhere (which is logical because I don't have any iso, I have the expanded tree on sdb1).
So I can't boot Ubuntu Server 16.04 from a USB stick.