I just buy another RPI3+ in order to install stellarmate on the PI . but i can't boot with ubuntu mate 16.04 installed on it .
the reason is this one find on internet . Ubuntu MATE does not boot on the 3B+ and 3A+. The Pi 3B and Pi 2B v1.2 use the first revision of the BCM2837 SoC, known as the BCM2837A0. The Pi 3B+ and 3A+ use the second revision of the BCM2837 SoC known as the BCM2837B0. This revision isn’t too different to the first revision other than the fact that it supports PoE (Power over Ethernet) and is clocked at 1.4GHz by default. For Pi models that use the BCM2837B0 to boot, the bootloader (bootcode.bin, *.elf, *.dat) needs to support this SoC. Unfortunately, Ubuntu MATE comes with an old version of the bootloader incompatible with the BCM2837B0. This is why you won’t get past the rainbow screen if you try to boot Ubuntu MATE on the 3B+ or 3A+.
Raspbian works well , is it possible to install Stellarmate on Raspbian or other system ?
So what I did is I found an image online where some people updated the ubuntu-mate image for 16.04 to boot on a Raspberry Pi 3b+. The official ubuntu mate distribution has not been updated to the latest pi, but numerous people have made images that do work. I don't remember right now which one I used, but I just did some google searches and tried one that said it was modified to work on the 3b+.