What else does uml need?

UML requires a root file system, which is nothing more than a file formatted as a file system (ex. Ext2) containing the contents of what a Linux install would need. Things like /etc, /usr, /sbin, /dev, etc.
By default, uml expects this file to be called root_fs.

UML requires a root file system, which is nothing more than a file formatted as a file system (ex. Ext2) containing the contents of what a Linux install would need. Things like /etc, /usr, /sbin, /dev, etc.