Celebrating 20 Years of Linux presence (1991 - 2011), Obviously Linux has running so far. a picture above give illustration of  a journey of Linux (kernel) since 1991 till now, a part of image above tells us that Ubuntu now dominate a Linux user for 34% by July 2011 followed by Redhat/Fedora for 28%. Check the following interesting facts :

Note : Illistration above is taken from Linux Foundation