Ubuntu Manpage: linux — User-mode Linux

Provided by: user-mode-linux_3.13.0-1um-0ubuntu1_amd64

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

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.

                                                                                         LINUX(1)

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

SEE ALSO

AUTHOR