Hello.
I downloaded image of Ubuntu Mate 16.04 for RP2/RP3, installed it on sd card with dd.
After i adjusted config file for proper video mode and power on RP3.
I can see correct picture on HDMI output but kernel panic during kernel
boot. It says that can not mount rootfs on unknown block device.
Seems it is bug.
I did not dig deeply, just for information.
I will answer to my self 
during dd on 8Gb card as usual all cards have different amount of blocks. So my sd card was little bit smaller and ext4 file system was corrupted so:
2053 e2fsck -f /dev/sdb2
2055 resize2fs /dev/sdb2
2056 fsck.ext4 -f /dev/sdb2
it fixed problem
Hi Mikchel
I got this kernel Panic. 
vfs unable to mount root fs on unknown-block(179 2)
I’m using a Scandisk 8GB Class 10 model number:SDSDQUAN-008G-G4A.
I’m new to this,i couldn’t understand . how you fixed it. 
Could you please explain how you fixed the issue step by step and help me out 
sorry ubuntu mate moderate,by mistake i clicked flag. please dont remove this topic