$ linux --help User Mode Linux v2.4.20-6um available at http://user-mode-linux.sourceforge.net/ --showconfig Prints the config file that this UML binary was generated from. mem=<Amount of desired ram> This controls how much "physical" memory the kernel allocates for the system. The size is specified as a number followed by one of 'k', 'K', 'm', 'M', which have the obvious meanings. This is not related to the amount of memory in the physical machine. It can be more, and the excess, if it's ever used, will just be swapped out. Example: mem=64M iomem=<name>,<file> Configure <file> as an IO memory region named <name>. --version Prints the version number of the kernel. root=<file containing the root fs> This is actually used by the generic kernel in exactly the same way as in any other kernel. If you configure a number of block devices and want to boot off something other than ubd0, you would use something like: root=/dev/ubd5 mode=tt When both CONFIG_MODE_TT and CONFIG_MODE_SKAS are enabled, this option forces UML to run in tt (tracing thread) mode. It is not the default because it's slower and less secure than skas mode. --help Prints this message. umid=<name> This is used to assign a unique identity to this UML machine and is used for naming the pid file and management console socket. uml_dir=<directory> The location to place the pid and umid files. initrd=<initrd image> This is used to boot UML from an initrd image. The argument is the name of the file containing the image. jail Enables the protection of kernel memory from processes. debug Starts up the kernel under the control of gdb. See the kernel debugging tutorial and the debugging session pages at http://user-mode-linux.sourceforge.net/ for more information. debugtrace Causes the tracing thread to pause until it is attached by a debugger and continued. This is mostly for debugging crashes early during boot, and should be pretty much obsoleted by the debug switch. honeypot This makes UML put process stacks in the same location as they are on the host, allowing expoits such as stack smashes to work against UML. This implies 'jail'. hostfs=<root dir>,<flags>,... This is used to set hostfs parameters. The root directory argument is used to confine all hostfs mounts to within the specified directory tree on the host. If this isn't specified, then a user inside UML can mount anything on the host that's accessible to the user that's running it. The only flag currently supported is 'append', which specifies that all files opened by hostfs will be opened in append mode. ssl[0-9]*=<channel description> Attach a console or serial line to a host channel. See http://user-mode-linux.sourceforge.net/input.html for a complete description of this switch. eth[0-9]+=<transport>,<options> Configure a network device. mconsole=notify:<socket> Requests that the mconsole driver send a message to the named Unix socket containing the name of the mconsole socket. This also serves to notify outside processes when UML has booted far enough to respond to mconsole requests. fake_ide Create ide0 entries that map onto ubd devices. ubd<n>=<filename> This is used to associate a device with a file in the underlying filesystem. Usually, there is a filesystem in the file, but that's not required. Swap devices containing swap files can be specified like this. Also, a file which doesn't contain a filesystem can have its contents read in the virtual machine by running dd on the device. n must be in the range 0 to 7. Appending an 'r' to the number will cause that device to be mounted read-only. For example ubd1r=./ext_fs. Appending an 's' (has to be _after_ 'r', if there is one) will cause data to be written to disk on the host immediately. fakehd Change the ubd device name to "hd". dsp=<dsp device> This is used to specify the host dsp device to the hostaudio driver. The default is "/dev/sound/dsp". mixer=<mixer device> This is used to specify the host mixer device to the hostaudio driver. The default is "/dev/sound/mixer". xterm=<terminal emulator>,<title switch>,<exec switch> Specifies an alternate terminal emulator to use for the debugger, consoles, and serial lines when they are attached to the xterm channel. The values are the terminal emulator binary, the switch it uses to set its title, and the switch it uses to execute a subprocess, respectively. The title switch must have the form '<switch> title', not '<switch>=title'. Similarly, the exec switch must have the form '<switch> command arg1 arg2 ...'. The default values are 'xterm=xterm,-T,-e'. Values for gnome-terminal are 'xterm=gnome-terminal,-t,-x'. con[0-9]*=<channel description> Attach a console or serial line to a host channel. See http://user-mode-linux.sourceforge.net/input.html for a complete description of this switch.