Provided by: user-mode-linux_3.2.0-1um-0ubuntu1_amd64 bug


       linux — User-mode Linux


       linux [options ...]


       This manual page briefly documents User-mode Linux.

       This  manual  page  was written for the Debian GNU/Linux distribution because the original
       program does not have a manual page.  Check linux --help for an up-to-date synopsis.


                 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.

                 Configure file as a named IO memory region named name.

                 gdb-pid is used to attach an external debugger to UML.  This may be an  already-
                 running gdb or a debugger-like process like strace.

                 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 exploits such as stack smashes to work against UML.

       debug     Starts up the kernel under the control of gdb. See the kernel debugging tutorial
                 and  the  debugging  session  pages  in the user-mode-linux-doc package for more

       root=file 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".
                 Another  notation  is  the  use of the major and the minor number of the device,
                 i.e. root=98:0, for ubd0.

                 To  use  hostfs  for  the  root  filesystem,  use  the  syntax   "root=/dev/root
                 rootflags=/ rootfstype=hostfs"

       umid=name This  is  used  to assign a unique identity to this UML machine This is used for
                 naming the pid file and  management  console  socket.  I.e.  to  access  to  the
                 management  console  for  an already running image (i.e. umid=test), just launch
                 uml_mconsole test from the host command line.

                 The location to place the pid and umid files.

                 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

                 Attach  a  console  to a host channel.  Examples of channels include ttys, ptys,
                 pts terminals, xterms, and file descriptors.

                 tty       This will make UML attach the device to the specified tty.  If the tty
                           that  you  specify  is the slave end of a tty/pty pair, something else
                           must have already opened the corresponding pty in order  for  this  to


                 pty       This  will  cause  UML to allocate a free host pty for the device. The
                           pty will be announced in the boot log. You would attach to it via  the
                           corresponding tty.


                 pts terminal
                           This  is  similar  to  pty above, but the specified UML device will be
                           attached to a free pts device on the host. Look at the boot log to see
                           which one.


                 xterm     UML will run an xterm and the device will be attached to it.


                 file descriptors
                           If  you  set  up  a  file  descriptor on the UML command line, you can
                           attach a UML device to it. This is most commonly used to put the  main
                           console  back  on  stdin  and  stdout  after  assigning  all the other
                           consoles to something else.

                           con0=fd:0,fd:1 con=xterm

                 You can also specify different input and output channels for a device by putting
                 a comma between them:


                 See    Setting    up    Serial    Lines    and    Consoles    (link    to    URL
                 file:///usr/share/doc/user-mode-linux-doc/html/input.html)     for    a     more

                 Attach  a  serial line to a host channel.  The same options are supported as for
                 consoles, described above.

       fake_ide  Create ide0 entries that map onto ubd devices.





                 This is used to associate a device with a file or 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. Appending an 'r'  will  cause  that  device  to  be
                 mounted  read-only.  Appending  an  's'  tells UML to open the file using O_SYNC
                 (synchronous I/O).

                 The ubd option can no longer be used to specify a hostfs root  filesystem.   See
                 the "root" option for a more correct method.

       udb       This option is here solely to catch ubd -> udb typos, which can be to impossible
                 to catch visually unless you specifically look for them. The only result of  any
                 option starting with 'udb' is an error in the boot output.

       fakehd    Change  the  ubd device name to "hd", allowing programs within UML to access UBD
                 devices as if they were normal IDE disks.

                 Configure  a  network  device.   Formats  and  examples  follow  (one  for  each
                 configured transport).











       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.

                 Disables  SKAS3  usage,  so that SKAS0 is used, unless you specify mode=tt. Note
                 that this was recently added - on older kernels you must use simply "skas0".

       skas0     Disables SKAS3 usage, so that SKAS0 is used, unless you specify mode=tt.

                 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.

       aio=2.4   This is used to force UML to use 2.4-style AIO even when 2.6 AIO  is  available.
                 2.4  AIO  is  a single thread that handles one request at a time, synchronously.
                 2.6 AIO is a thread which uses the 2.6 AIO  interface  to  handle  an  arbitrary
                 number  of pending requests.  2.6 AIO is not available in tt mode, on 2.4 hosts,
                 or when UML is  built  with  /usr/include/linux/aio_abi.h  not  available.  Many
                 distributions don't include aio_abi.h, so you will need to copy it from a kernel
                 tree to your /usr/include/linux in order to build an AIO-capable UML.

                 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.

       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
                 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-

                 Turns off usage of PTRACE_LDT, even if host supports it.  To support PTRACE_LDT,
                 the host needs to be patched using the current skas3 patch.

                 Turns off usage of PTRACE_FAULTINFO,  even  if  host  supports  it.  To  support
                 PTRACE_FAULTINFO, the host needs to be patched using the current skas3 patch.

       noprocmm  Turns off usage of /proc/mm, even if host supports it.  To support /proc/mm, the
                 host needs to be patched using the current skas3 patch.

       nosysemu  Turns off  syscall  emulation  patch  for  ptrace  (SYSEMU)  on.   SYSEMU  is  a
                 performance-patch introduced by Laurent Vivier. It changes behaviour of ptrace()
                 and helps reducing host context switch rate.  To make it  working,  you  need  a
                 kernel         patch        for        your        host,        too.         See
        for further information.

       --help    Prints syntax information.

       --version Prints the version number of the kernel.

                 Prints the configuration used to build the kernel.  To  print  all  the  options
                 used to build the "linux" uml kernel and save them in "config_file" you can use

                 linux --showconfig > config_file


       The    UserModeLinux-HOWTO    (link    to    URL    file:///usr/share/doc/user-mode-linux-


       User-mode Linux was written by Jeff Dike and others.

       This manual page was written by Matt Zimmerman  for  the  Debian  GNU/Linux
       system, based on linux --help       and the user-mode-linux website.