Ubuntu for phones uses a fork of Linux
Most distros use their own fork of the linux kernel. There's nothing wrong with that
"In the same way, even though God has the right to show his anger and his power, he is very patient with those on whom his anger falls, who are destined for destruction."
-- Romans 9:22
"...a most excellent barbarian ... Genghis Kahn!" -- _Bill And Ted's Excellent Adventure_