poky: subtree update:0ac99625bf..796be0593a
Alexander Kanavin (31):
netbase: upgrade 6.1 -> 6.2
meson: upgrade 0.55.1 -> 0.56.0
vulkan-samples: update to latest revision
libcap: update 2.44 -> 2.45
bind: upgrade 9.16.7 -> 9.16.9
quota: upgrade 4.05 -> 4.06
pango: upgrade 1.46.2 -> 1.48.0
elfutils: upgrade 0.181 -> 0.182
ifupdown: upgrade 0.8.35 -> 0.8.36
createrepo-c: upgrade 0.16.1 -> 0.16.2
acpica: upgrade 20200925 -> 20201113
grep: upgrade 3.5 -> 3.6
man-pages: upgrade 5.08 -> 5.09
stress-ng: upgrade 0.11.23 -> 0.11.24
libhandy: upgrade 1.0.1 -> 1.0.2
piglit: upgrade to latest revision
xkbcomp: upgrade 1.4.3 -> 1.4.4
lz4: upgrade 1.9.2 -> 1.9.3
bison: upgrade 3.7.3 -> 3.7.4
python3-setuptools-scm: fix upstream version check
cantarell-fonts: update 0.0.25 -> 0.201
meta/lib/oe/reproducible.py: gitsm:// works just as fine as git:// for timestamps
llvm: fix reproducibility
ruby: fix reproducibility
webkitgtk: fix reproducibility
ffmpeg: fix reproducibility
piglit: fix reproducibility
serf: do not install the static library
llvm: sort the lists in generated source reproducibibly
kea: fix reproducibility
poky.conf: do not write current date into distro version, use git hash instead
Andrej Valek (1):
kernel-dummy: fix executing unexpected tasks
Anuj Mittal (1):
releases.rst: add gatesgarth to current releases
Brett Warren (1):
libffi: add patch to revert clang VFP workaround
Chandana kalluri (1):
populate_sdk_ext: use SDK_CUSTOM_TEPLATECONF variable to enable custom templateconf.cfg
Changqing Li (1):
buildtools-tarball: add wic dependency into extended buildtools
Diego Sueiro (2):
modutils-initscripts: Fix modules.dep creation when USE_DEPMOD="0"
initscripts: Change execution order between checkroot and modutils
Dmitry Baryshkov (2):
linux-firmware: upgrade 20201022 -> 20201118
linux-firmware: package ath11k firmware
Fabio Berton (1):
mesa: Update 20.2.1 -> 20.2.4
Gratian Crisan (1):
kernel-module-split.bbclass: fix kernel modules getting marked as CONFFILES
Jack Mitchell (3):
Revert "connman: set service to conflict with systemd-networkd"
systemd-conf: add PACKAGECONFIG to enable/disable auto ethernet DHCP
systemd-conf: match ethernet interfaces by type rather than globbing
Joshua Watt (2):
bitbake: hashserv: client: Fix AF_UNIX path length limits
bitbake: hashserv: Fix broken AF_UNIX path length limit
Kai Kang (2):
systemd-systemctl-native: capable to call without argument
systemd.bbclass: update command to check systemctl available
Kevin Hao (1):
tune-octeontx2.inc: Add tune for Marvell OCTEON TX2 core
Li Wang (2):
qemu: CVE-2020-29129 CVE-2020-29130
qemu: CVE-2020-25624
Luca Boccassi (1):
dbus: move messagebus user to dbus-common package
Michael Halstead (1):
releases: conf: add link to 3.1.4, update to include 3.1.4
Nicolas Dechesne (19):
sphinx: add .vscode in .gitignore
{dev,kernel,sdk}-manual: replace hardcoded release version with &DISTRO;
sphinx: replace bitbake labels with references to corresponding title
brief-yoctoprojectqs: replace labels with references to section title
dev-manual: replace labels with references to section title
ref-manual: replace labels with references to section title
sdk-manual: replace labels with references to section title
overview-manual: remove unused labels
dev-manual: remove unused labels
sphinx: rename top level document in each manual
sphinx: use absolute paths for :doc: references
test-manual: remove 'test-manual' from filenames
toaster-manual: remove 'toaster-manual' from filenames
dev-manual: remove 'dev-manual' from filenames
kernel-dev: remove 'kernel-dev' from filenames
profile-manual: remove 'profile-manual' from filenames
overview-manual: remove 'overview-manual' from filenames
sdk-manual: remove 'sdk' from filenames
ref-manual: remove 'ref' from filenames
Paul Barker (5):
documentation: Simplify yocto_wiki links
documentation: Simplify yocto_git links
ref-manual: Simplify oe_git links
poky.conf: Add opensuseleap-15.2 and fedora-33 to tested distros
poky.conf: Drop fedora-30 from tested distros
Peter Kjellerstedt (2):
pseudo: Simplify pseudo_client_ignore_path_chroot()
bitbake.conf: Add all layers (from BBLAYERS) to PSEUDO_IGNORE_PATHS
Richard Purdie (8):
lz4: Use the new branch naming from upstream
Revert "bitbake.conf: Add all layers (from BBLAYERS) to PSEUDO_IGNORE_PATHS"
build-appliance-image: Update to master head revision
bitbake: Revert "fetch2: use relative symlinks for anything pulled from PREMIRRORS"
build-appliance-image: Update to master head revision
metadata_scm: Fix signature handling of METADATA_REVISION and METADATA_BRANCH
poky: Set SDK_VERSION explicitly
build-appliance-image: Update to master head revision
Ross Burton (9):
oeqa/devtool: use Yocto mirror for pv-1.5.3 tarball
image_types: remove obsolete tar comment
image_types: sort tarball file listings
package_manager/ipk: neaten OPKGLIBDIR logic
ldconfig-native: don't write auxiliary cache
package_manager/ipk: improve remove_packaging_data
oeqa/selftest/containerimage: update for improved cleanup
coreutils: add SUSE-specific issues to CVE whitelist
bitbake: msg: use safe YAML loader
Sinan Kaya (1):
poky-tiny: enable section removal
Tomasz Dziendzielski (1):
pseudo: Update to print PSEUDO_LOGFILE in abort message on path mismatches
sangeeta jain (1):
meta/lib/oeqa/manual/oe-core.json: Update test_bitbake_devshell
zangrc (3):
libinput: upgrade 1.16.3 -> 1.16.4
lighttpd: upgrade 1.4.55 -> 1.4.56
sysstat: upgrade 12.4.0 -> 12.4.1
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: I65f2f1c9d44433f3e62609240012c42256679b51
diff --git a/poky/documentation/dev-manual/qemu.rst b/poky/documentation/dev-manual/qemu.rst
new file mode 100644
index 0000000..766691b
--- /dev/null
+++ b/poky/documentation/dev-manual/qemu.rst
@@ -0,0 +1,463 @@
+.. SPDX-License-Identifier: CC-BY-SA-2.0-UK
+
+*******************************
+Using the Quick EMUlator (QEMU)
+*******************************
+
+The Yocto Project uses an implementation of the Quick EMUlator (QEMU)
+Open Source project as part of the Yocto Project development "tool set".
+This chapter provides both procedures that show you how to use the Quick
+EMUlator (QEMU) and other QEMU information helpful for development
+purposes.
+
+Overview
+========
+
+Within the context of the Yocto Project, QEMU is an emulator and
+virtualization machine that allows you to run a complete image you have
+built using the Yocto Project as just another task on your build system.
+QEMU is useful for running and testing images and applications on
+supported Yocto Project architectures without having actual hardware.
+Among other things, the Yocto Project uses QEMU to run automated Quality
+Assurance (QA) tests on final images shipped with each release.
+
+.. note::
+
+ This implementation is not the same as QEMU in general.
+
+This section provides a brief reference for the Yocto Project
+implementation of QEMU.
+
+For official information and documentation on QEMU in general, see the
+following references:
+
+- `QEMU Website <https://wiki.qemu.org/Main_Page>`__\ *:* The official
+ website for the QEMU Open Source project.
+
+- `Documentation <https://wiki.qemu.org/Manual>`__\ *:* The QEMU user
+ manual.
+
+Running QEMU
+============
+
+To use QEMU, you need to have QEMU installed and initialized as well as
+have the proper artifacts (i.e. image files and root filesystems)
+available. Follow these general steps to run QEMU:
+
+1. *Install QEMU:* QEMU is made available with the Yocto Project a
+ number of ways. One method is to install a Software Development Kit
+ (SDK). See ":ref:`sdk-manual/intro:the qemu emulator`" section in the
+ Yocto Project Application Development and the Extensible Software
+ Development Kit (eSDK) manual for information on how to install QEMU.
+
+2. *Setting Up the Environment:* How you set up the QEMU environment
+ depends on how you installed QEMU:
+
+ - If you cloned the ``poky`` repository or you downloaded and
+ unpacked a Yocto Project release tarball, you can source the build
+ environment script (i.e. :ref:`structure-core-script`):
+ ::
+
+ $ cd ~/poky
+ $ source oe-init-build-env
+
+ - If you installed a cross-toolchain, you can run the script that
+ initializes the toolchain. For example, the following commands run
+ the initialization script from the default ``poky_sdk`` directory:
+ ::
+
+ . ~/poky_sdk/environment-setup-core2-64-poky-linux
+
+3. *Ensure the Artifacts are in Place:* You need to be sure you have a
+ pre-built kernel that will boot in QEMU. You also need the target
+ root filesystem for your target machine's architecture:
+
+ - If you have previously built an image for QEMU (e.g. ``qemux86``,
+ ``qemuarm``, and so forth), then the artifacts are in place in
+ your :term:`Build Directory`.
+
+ - If you have not built an image, you can go to the
+ :yocto_dl:`machines/qemu </releases/yocto/yocto-&DISTRO;/machines/qemu/>` area and download a
+ pre-built image that matches your architecture and can be run on
+ QEMU.
+
+ See the ":ref:`sdk-manual/appendix-obtain:extracting the root filesystem`"
+ section in the Yocto Project Application Development and the
+ Extensible Software Development Kit (eSDK) manual for information on
+ how to extract a root filesystem.
+
+4. *Run QEMU:* The basic ``runqemu`` command syntax is as follows:
+ ::
+
+ $ runqemu [option ] [...]
+
+ Based on what you provide on the command
+ line, ``runqemu`` does a good job of figuring out what you are trying
+ to do. For example, by default, QEMU looks for the most recently
+ built image according to the timestamp when it needs to look for an
+ image. Minimally, through the use of options, you must provide either
+ a machine name, a virtual machine image (``*wic.vmdk``), or a kernel
+ image (``*.bin``).
+
+ Here are some additional examples to help illustrate further QEMU:
+
+ - This example starts QEMU with MACHINE set to "qemux86-64".
+ Assuming a standard
+ :term:`Build Directory`, ``runqemu``
+ automatically finds the ``bzImage-qemux86-64.bin`` image file and
+ the ``core-image-minimal-qemux86-64-20200218002850.rootfs.ext4``
+ (assuming the current build created a ``core-image-minimal``
+ image).
+
+ .. note::
+
+ When more than one image with the same name exists, QEMU finds
+ and uses the most recently built image according to the
+ timestamp.
+
+ ::
+
+ $ runqemu qemux86-64
+
+ - This example produces the exact same results as the previous
+ example. This command, however, specifically provides the image
+ and root filesystem type.
+ ::
+
+ $ runqemu qemux86-64 core-image-minimal ext4
+
+ - This example specifies to boot an initial RAM disk image and to
+ enable audio in QEMU. For this case, ``runqemu`` set the internal
+ variable ``FSTYPE`` to "cpio.gz". Also, for audio to be enabled,
+ an appropriate driver must be installed (see the previous
+ description for the ``audio`` option for more information).
+ ::
+
+ $ runqemu qemux86-64 ramfs audio
+
+ - This example does not provide enough information for QEMU to
+ launch. While the command does provide a root filesystem type, it
+ must also minimally provide a `MACHINE`, `KERNEL`, or `VM` option.
+ ::
+
+ $ runqemu ext4
+
+ - This example specifies to boot a virtual machine image
+ (``.wic.vmdk`` file). From the ``.wic.vmdk``, ``runqemu``
+ determines the QEMU architecture (`MACHINE`) to be "qemux86-64" and
+ the root filesystem type to be "vmdk".
+ ::
+
+ $ runqemu /home/scott-lenovo/vm/core-image-minimal-qemux86-64.wic.vmdk
+
+Switching Between Consoles
+==========================
+
+When booting or running QEMU, you can switch between supported consoles
+by using Ctrl+Alt+number. For example, Ctrl+Alt+3 switches you to the
+serial console as long as that console is enabled. Being able to switch
+consoles is helpful, for example, if the main QEMU console breaks for
+some reason.
+
+.. note::
+
+ Usually, "2" gets you to the main console and "3" gets you to the
+ serial console.
+
+Removing the Splash Screen
+==========================
+
+You can remove the splash screen when QEMU is booting by using Alt+left.
+Removing the splash screen allows you to see what is happening in the
+background.
+
+Disabling the Cursor Grab
+=========================
+
+The default QEMU integration captures the cursor within the main window.
+It does this since standard mouse devices only provide relative input
+and not absolute coordinates. You then have to break out of the grab
+using the "Ctrl+Alt" key combination. However, the Yocto Project's
+integration of QEMU enables the wacom USB touch pad driver by default to
+allow input of absolute coordinates. This default means that the mouse
+can enter and leave the main window without the grab taking effect
+leading to a better user experience.
+
+Running Under a Network File System (NFS) Server
+================================================
+
+One method for running QEMU is to run it on an NFS server. This is
+useful when you need to access the same file system from both the build
+and the emulated system at the same time. It is also worth noting that
+the system does not need root privileges to run. It uses a user space
+NFS server to avoid that. Follow these steps to set up for running QEMU
+using an NFS server.
+
+1. *Extract a Root Filesystem:* Once you are able to run QEMU in your
+ environment, you can use the ``runqemu-extract-sdk`` script, which is
+ located in the ``scripts`` directory along with the ``runqemu``
+ script.
+
+ The ``runqemu-extract-sdk`` takes a root filesystem tarball and
+ extracts it into a location that you specify. Here is an example that
+ takes a file system and extracts it to a directory named
+ ``test-nfs``:
+
+ .. code-block:: none
+
+ runqemu-extract-sdk ./tmp/deploy/images/qemux86-64/core-image-sato-qemux86-64.tar.bz2 test-nfs
+
+2. *Start QEMU:* Once you have extracted the file system, you can run
+ ``runqemu`` normally with the additional location of the file system.
+ You can then also make changes to the files within ``./test-nfs`` and
+ see those changes appear in the image in real time. Here is an
+ example using the ``qemux86`` image:
+
+ .. code-block:: none
+
+ runqemu qemux86-64 ./test-nfs
+
+.. note::
+
+ Should you need to start, stop, or restart the NFS share, you can use
+ the following commands:
+
+ - The following command starts the NFS share:
+ ::
+
+ runqemu-export-rootfs start file-system-location
+
+ - The following command stops the NFS share:
+ ::
+
+ runqemu-export-rootfs stop file-system-location
+
+ - The following command restarts the NFS share:
+ ::
+
+ runqemu-export-rootfs restart file-system-location
+
+QEMU CPU Compatibility Under KVM
+================================
+
+By default, the QEMU build compiles for and targets 64-bit and x86 Intel
+Core2 Duo processors and 32-bit x86 Intel Pentium II processors. QEMU
+builds for and targets these CPU types because they display a broad
+range of CPU feature compatibility with many commonly used CPUs.
+
+Despite this broad range of compatibility, the CPUs could support a
+feature that your host CPU does not support. Although this situation is
+not a problem when QEMU uses software emulation of the feature, it can
+be a problem when QEMU is running with KVM enabled. Specifically,
+software compiled with a certain CPU feature crashes when run on a CPU
+under KVM that does not support that feature. To work around this
+problem, you can override QEMU's runtime CPU setting by changing the
+``QB_CPU_KVM`` variable in ``qemuboot.conf`` in the
+:term:`Build Directory` ``deploy/image``
+directory. This setting specifies a ``-cpu`` option passed into QEMU in
+the ``runqemu`` script. Running ``qemu -cpu help`` returns a list of
+available supported CPU types.
+
+QEMU Performance
+================
+
+Using QEMU to emulate your hardware can result in speed issues depending
+on the target and host architecture mix. For example, using the
+``qemux86`` image in the emulator on an Intel-based 32-bit (x86) host
+machine is fast because the target and host architectures match. On the
+other hand, using the ``qemuarm`` image on the same Intel-based host can
+be slower. But, you still achieve faithful emulation of ARM-specific
+issues.
+
+To speed things up, the QEMU images support using ``distcc`` to call a
+cross-compiler outside the emulated system. If you used ``runqemu`` to
+start QEMU, and the ``distccd`` application is present on the host
+system, any BitBake cross-compiling toolchain available from the build
+system is automatically used from within QEMU simply by calling
+``distcc``. You can accomplish this by defining the cross-compiler
+variable (e.g. ``export CC="distcc"``). Alternatively, if you are using
+a suitable SDK image or the appropriate stand-alone toolchain is
+present, the toolchain is also automatically used.
+
+.. note::
+
+ Several mechanisms exist that let you connect to the system running
+ on the QEMU emulator:
+
+ - QEMU provides a framebuffer interface that makes standard consoles
+ available.
+
+ - Generally, headless embedded devices have a serial port. If so,
+ you can configure the operating system of the running image to use
+ that port to run a console. The connection uses standard IP
+ networking.
+
+ - SSH servers exist in some QEMU images. The ``core-image-sato``
+ QEMU image has a Dropbear secure shell (SSH) server that runs with
+ the root password disabled. The ``core-image-full-cmdline`` and
+ ``core-image-lsb`` QEMU images have OpenSSH instead of Dropbear.
+ Including these SSH servers allow you to use standard ``ssh`` and
+ ``scp`` commands. The ``core-image-minimal`` QEMU image, however,
+ contains no SSH server.
+
+ - You can use a provided, user-space NFS server to boot the QEMU
+ session using a local copy of the root filesystem on the host. In
+ order to make this connection, you must extract a root filesystem
+ tarball by using the ``runqemu-extract-sdk`` command. After
+ running the command, you must then point the ``runqemu`` script to
+ the extracted directory instead of a root filesystem image file.
+ See the "`Running Under a Network File System (NFS)
+ Server <#qemu-running-under-a-network-file-system-nfs-server>`__"
+ section for more information.
+
+QEMU Command-Line Syntax
+========================
+
+The basic ``runqemu`` command syntax is as follows:
+::
+
+ $ runqemu [option ] [...]
+
+Based on what you provide on the command line, ``runqemu`` does a
+good job of figuring out what you are trying to do. For example, by
+default, QEMU looks for the most recently built image according to the
+timestamp when it needs to look for an image. Minimally, through the use
+of options, you must provide either a machine name, a virtual machine
+image (``*wic.vmdk``), or a kernel image (``*.bin``).
+
+Following is the command-line help output for the ``runqemu`` command:
+::
+
+ $ runqemu --help
+
+ Usage: you can run this script with any valid combination
+ of the following environment variables (in any order):
+ KERNEL - the kernel image file to use
+ ROOTFS - the rootfs image file or nfsroot directory to use
+ MACHINE - the machine name (optional, autodetected from KERNEL filename if unspecified)
+ Simplified QEMU command-line options can be passed with:
+ nographic - disable video console
+ serial - enable a serial console on /dev/ttyS0
+ slirp - enable user networking, no root privileges is required
+ kvm - enable KVM when running x86/x86_64 (VT-capable CPU required)
+ kvm-vhost - enable KVM with vhost when running x86/x86_64 (VT-capable CPU required)
+ publicvnc - enable a VNC server open to all hosts
+ audio - enable audio
+ [*/]ovmf* - OVMF firmware file or base name for booting with UEFI
+ tcpserial=<port> - specify tcp serial port number
+ biosdir=<dir> - specify custom bios dir
+ biosfilename=<filename> - specify bios filename
+ qemuparams=<xyz> - specify custom parameters to QEMU
+ bootparams=<xyz> - specify custom kernel parameters during boot
+ help, -h, --help: print this text
+
+ Examples:
+ runqemu
+ runqemu qemuarm
+ runqemu tmp/deploy/images/qemuarm
+ runqemu tmp/deploy/images/qemux86/<qemuboot.conf>
+ runqemu qemux86-64 core-image-sato ext4
+ runqemu qemux86-64 wic-image-minimal wic
+ runqemu path/to/bzImage-qemux86.bin path/to/nfsrootdir/ serial
+ runqemu qemux86 iso/hddimg/wic.vmdk/wic.qcow2/wic.vdi/ramfs/cpio.gz...
+ runqemu qemux86 qemuparams="-m 256"
+ runqemu qemux86 bootparams="psplash=false"
+ runqemu path/to/<image>-<machine>.wic
+ runqemu path/to/<image>-<machine>.wic.vmdk
+
+``runqemu`` Command-Line Options
+================================
+
+Following is a description of ``runqemu`` options you can provide on the
+command line:
+
+.. note::
+
+ If you do provide some "illegal" option combination or perhaps you do
+ not provide enough in the way of options, ``runqemu``
+ provides appropriate error messaging to help you correct the problem.
+
+- `QEMUARCH`: The QEMU machine architecture, which must be "qemuarm",
+ "qemuarm64", "qemumips", "qemumips64", "qemuppc", "qemux86", or
+ "qemux86-64".
+
+- `VM`: The virtual machine image, which must be a ``.wic.vmdk``
+ file. Use this option when you want to boot a ``.wic.vmdk`` image.
+ The image filename you provide must contain one of the following
+ strings: "qemux86-64", "qemux86", "qemuarm", "qemumips64",
+ "qemumips", "qemuppc", or "qemush4".
+
+- `ROOTFS`: A root filesystem that has one of the following filetype
+ extensions: "ext2", "ext3", "ext4", "jffs2", "nfs", or "btrfs". If
+ the filename you provide for this option uses "nfs", it must provide
+ an explicit root filesystem path.
+
+- `KERNEL`: A kernel image, which is a ``.bin`` file. When you provide a
+ ``.bin`` file, ``runqemu`` detects it and assumes the file is a
+ kernel image.
+
+- `MACHINE`: The architecture of the QEMU machine, which must be one of
+ the following: "qemux86", "qemux86-64", "qemuarm", "qemuarm64",
+ "qemumips", "qemumips64", or "qemuppc". The MACHINE and QEMUARCH
+ options are basically identical. If you do not provide a MACHINE
+ option, ``runqemu`` tries to determine it based on other options.
+
+- ``ramfs``: Indicates you are booting an initial RAM disk (initramfs)
+ image, which means the ``FSTYPE`` is ``cpio.gz``.
+
+- ``iso``: Indicates you are booting an ISO image, which means the
+ ``FSTYPE`` is ``.iso``.
+
+- ``nographic``: Disables the video console, which sets the console to
+ "ttys0". This option is useful when you have logged into a server and
+ you do not want to disable forwarding from the X Window System (X11)
+ to your workstation or laptop.
+
+- ``serial``: Enables a serial console on ``/dev/ttyS0``.
+
+- ``biosdir``: Establishes a custom directory for BIOS, VGA BIOS and
+ keymaps.
+
+- ``biosfilename``: Establishes a custom BIOS name.
+
+- ``qemuparams=\"xyz\"``: Specifies custom QEMU parameters. Use this
+ option to pass options other than the simple "kvm" and "serial"
+ options.
+
+- ``bootparams=\"xyz\"``: Specifies custom boot parameters for the
+ kernel.
+
+- ``audio``: Enables audio in QEMU. The MACHINE option must be either
+ "qemux86" or "qemux86-64" in order for audio to be enabled.
+ Additionally, the ``snd_intel8x0`` or ``snd_ens1370`` driver must be
+ installed in linux guest.
+
+- ``slirp``: Enables "slirp" networking, which is a different way of
+ networking that does not need root access but also is not as easy to
+ use or comprehensive as the default.
+
+- ``kvm``: Enables KVM when running "qemux86" or "qemux86-64" QEMU
+ architectures. For KVM to work, all the following conditions must be
+ met:
+
+ - Your MACHINE must be either qemux86" or "qemux86-64".
+
+ - Your build host has to have the KVM modules installed, which are
+ ``/dev/kvm``.
+
+ - The build host ``/dev/kvm`` directory has to be both writable and
+ readable.
+
+- ``kvm-vhost``: Enables KVM with VHOST support when running "qemux86"
+ or "qemux86-64" QEMU architectures. For KVM with VHOST to work, the
+ following conditions must be met:
+
+ - `kvm <#kvm-cond>`__ option conditions must be met.
+
+ - Your build host has to have virtio net device, which are
+ ``/dev/vhost-net``.
+
+ - The build host ``/dev/vhost-net`` directory has to be either
+ readable or writable and "slirp-enabled".
+
+- ``publicvnc``: Enables a VNC server open to all hosts.