User Mode Linux: Coming to a Kernel Near You, Part 1

18/03/2003 Written by Eric Lubow

There are a num­ber of fun­da­men­tal addi­tions com­ing in the next Linux ker­nel. One of these will be a great boon to soft­ware devel­op­ers, beta testers, prod­uct review­ers, host­ing ser­vices, and more: User Mode Linux (UML). Just as VMware allows us to run a machine within a machine, UML lets us do run mul­ti­ple, sep­a­rate, iso­lated instances of Linux on a sin­gle Linux box.
Seems a bit too good to be true, doesn’t it? Let’s take a closer look at UML, how it works, and the pros and cons involved in deter­min­ing if this upcom­ing ker­nel fea­ture is for you.
The name for this fea­ture isn’t the most self-​explanatory. User Mode Linux is thusly named because it runs in user space. With a UML, you can run a minia­ture Linux sys­tem with its own ker­nel and filesys­tem with­out need­ing root access to the entire machine. Your UML is your own lit­tle world, and you can con­fig­ure its ker­nel, net­work­ing, and all other aspects of the vir­tual machine to your satisfaction.