Device and Hardware Specifications


The following options set configurations for virtual devices and hardware.

  • dsp=dsp device and mixer=mixer device These two options specify the host audio interfaces for the use of the UML audio pass-through driver. The default values are /dev/sound/dsp and /dev/sound/mixer, respectively. If you wish to play sound from within your UML instance, and the host digital signal processor (dsp) or mixer devices are different from these, you'll need to use these switches.

  • xterm=terminal emulator, title switch, exec switch This switch allows the use of terminal emulators besides xterm for UML consoles and serial lines. The arguments specify how to invoke the emulator with a given title and command running within it. The defaults, for xterm, are -T and -e, meaning that the title is specified with the -T switch and the command to run within the xterm follows the -e switch. The values for gnome-terminal are -t and -x, so xterm=gnome-terminal,-t,-x would make UML use gnome-terminal instead of xterm.

  • initrd=initrd image This switch makes UML boot from an initial ramdisk (initrd) image. The image must be specified as a filename on the host.

  • iomem=name, file This specifies the use of a host file as an I/O memory (iomem) region. name is the name of the driver that is going to own the region of memory. file is the name of the host file to be mapped into the UML instance's physical memory region. A demo iomem driver can be found in arch/um/drivers/ mmapper_kern.c in the UML source tree.

  • mem=size Use this to specify the size of the UML instance's physical memory as a certain number of kilobytes, megabytes, or gigabytes via the K, M, or G suffixes, respectively. This has no relation to the amount of physical memory on the host. The UML instance's memory size can be either less or more than the host's memory size. If the UML memory size is more, and it is all used by the UML instance, the host will swap out the portion of the UML instance's memory that it thinks hasn't been used recently.

  • root=root device This option specifies the device containing the root filesystem. By default, it is /dev/ubda.

  • ncpus=n With CONFIG_SMP enabled, this switch specifies the number of virtual processors in the UML instance. If this is less than or equal to the number of processors on the host, the switch will enable that many threads to be running simultaneously, subject to scheduling decisions on the host. If there are more virtual processors than host processors, you can use this switch to determine the amount of host CPU power the UML instances can consume relative to each other. For example, a UML instance with four processors is entitled to twice as much host CPU time as an instance with two processors.

  • ethn=interface configuration This configures the host side of a network interface, making the device available and able to receive and transmit packets. The interface configuration is summarized in Table 8.1 and described completely in Chapter 7.

  • fake_ide This switch creates IDE entries in /proc that correspond to the ubd devices in the UML instance, which sometimes helps make distribution install procedures work inside UML.

  • ubd<n><flags>=filename[:filename This configures a UML block device on the host. n specifies the device to be configured; either letters (a through z) or numbers can be used. Letters are preferred because they don't encourage the belief that the unit number on the command line is the same as the minor number within UML. ubda (and ubd0) has minor number 0 and ubdb (and ubd1) has minor number 16 since each device can have up to 16 partitions.

    flags can be one or more of the following.

    - r The device is read-onlyread-write mounts will fail, as will any attempt to write anything to the device.

    - s All I/O to the host will be done synchronously (O_SYNC will be set).

    - d This device is to be considered as strictly data (i.e., even if it looks like a COW file, it is to be treated as a standalone device).

    - c This device will be shared writable between this UML instance and something else, normally another UML instance.

    This would generally be done through a cluster filesystem.

    Either one or two filenames may be provided, separated by either a comma or a colon. If two filenames are specified, the first is a COW file and the second is its backing file. You can obtain the same effect by specifying the COW file by itself, as it contains the location of its backing file. Separating the two files by a colon allows shell filename completion to work on the second file.

  • udb This option exists for the sole purpose of catching ubd to udb typos, which can be impossible to spot visually unless you are specifically looking for them. Adding this to the UML command line will simply cause a warning to be printed, alerting you to the typo.




User Mode Linux
User Mode Linux
ISBN: 0131865056
EAN: 2147483647
Year: N/A
Pages: 116
Authors: Jeff Dike

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