NAME¶
linux — User-mode Linux
SYNOPSIS¶
linux [
options ...]
DESCRIPTION¶
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.
OPTIONS¶
- mem=memory
- 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.
- iomem=name,file
- Configure file as a named IO memory region named
name.
- gdb-pid=pid
- 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.
- 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 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 information.
- 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.
- uml_dir=directory
- The location to place the pid and umid files.
- initrd=file
- 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
- con[0-9]*=description
- 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
work.
con1=tty:/dev/tty3
- 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.
con1=pty
- 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.
con1=pts
- xterm
- UML will run an xterm and the device will be attached to
it.
con1=xterm
- 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:
ssl3=tty:/dev/tty2,xterm
-
- See Setting up Serial Lines and Consoles (link to
URL file:///usr/share/doc/user-mode-linux-doc/html/input.html) for a
more information.
- ssl[0-9]*=description
- 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.
- ubd[0-7][r][s]=file
-
-
-
ubd0r=/tmp/debian-woody.ext2
-
-
ubd0rs=/tmp/debian-woody.ext2
-
-
ubd0=/tmp/chroot
-
- 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.
- eth[0-9]+=transport,options
- Configure a network device. Formats and examples follow
(one for each configured transport).
-
- eth[0-9]+=ethertap,device,ethernet_address,tap_ip_address
-
-
eth0=ethertap,tap0,,192.168.0.1
-
- eth[0-9]+=tuntap,,ethernet_address,ip_address
-
-
eth0=tuntap,,fe:fd:0:0:0:1,192.168.0.1
-
- eth[0-9]+=daemon,ethernet_address,type,control_socket,data_socket
-
-
eth0=daemon,,unix,/var/run/uml-utilities/uml_switch.ctl
-
- eth[0-9]+=slip,slip_ip
-
-
eth0=slip,192.168.0.1
-
- eth[0-9]+=mcast,ethernet_address,address,port,ttl
-
-
eth0=mcast,,224.2.3.4:5555,3
- 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.
- mode=skas0
- 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.
- 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.
- 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.
- hostfs=rootdir,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.
- 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-terminal,-t,-x'.
- noptraceldt
- 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.
- noptracefaultinfo
- 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
http://perso.wanadoo.fr/laurent.vivier/UML/ for further information.
- --help
- Prints syntax information.
- --version
- Prints the version number of the kernel.
- --showconfig
- 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
SEE ALSO¶
The
UserModeLinux-HOWTO (link to URL
file:///usr/share/doc/user-mode-linux-doc/html/UserModeLinux-HOWTO.html)
AUTHOR¶
User-mode Linux was written by Jeff Dike and others.
This manual page was written by Matt Zimmerman mdz@debian.org for the
Debian
GNU/Linux system, based on
linux --help and the user-mode-linux
website.