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86 lines
4.1 KiB
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86 lines
4.1 KiB
Plaintext
New console I/O infrastructure in Xen 1.3
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=========================================
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Keir Fraser, University of Cambridge, 3rd June 2004
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I thought I'd write a quick note about using the new console I/O
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infrastructure in Xen 1.3. Significant new features compared with 1.2,
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and with older revisions of 1.3, include:
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- bi-directional console access
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- log in to a Xenolinux guest OS via its virtual console
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- a new terminal client (replaces the use of telnet in character mode)
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- proper handling of terminal emulation
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Accessing the virtual console from within the guest OS
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------------------------------------------------------
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Every Xenolinux instance owns a bidirectional 'virtual console'.
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The device node to which this console is attached can be configured
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by specifying 'xencons=' on the OS command line:
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'xencons=off' --> disable virtual console
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'xencons=tty' --> attach console to /dev/tty1 (tty0 at boot-time)
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'xencons=ttyS' --> attach console to /dev/ttyS0
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The default is to attach to /dev/tty1, and also to create dummy
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devices for /dev/tty2-63 to avoid warnings from many standard distro
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startup scripts. The exception is domain 0, which by default attaches
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to /dev/ttyS0.
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Domain 0 virtual console
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------------------------
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The virtual console for domain 0 is shared with Xen's console. For
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example, if you specify 'console=com1' as a boot parameter to Xen,
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then domain 0 will have bi-directional access to the primary serial
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line. Boot-time messages can be directed to the virtual console by
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specifying 'console=ttyS0' as a boot parameter to Xenolinux.
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Connecting to the virtual console
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---------------------------------
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Domain 0 console may be accessed using the supplied 'miniterm' program
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if raw serial access is desired. If the Xen machine is connected to a
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serial-port server, then the supplied 'xencons' program may be used to
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connect to the appropriate TCP port on the server:
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# xencons <server host> <server port>
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Logging in via virtual console
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------------------------------
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It is possible to log in to a guest OS via its virtual console if a
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'getty' is running. In most domains the virtual console is named tty1
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so standard startup scripts and /etc/inittab should work
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fine. Furthermore, tty2-63 are created as dummy console devices to
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suppress warnings from standard startup scripts. If the OS has
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attached the virtual console to /dev/ttyS0 then you will need to
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start a 'mingetty' on that device node.
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Virtual console for other domains
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---------------------------------
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Every guest OS has a virtual console that is accessible via
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'console=tty0' at boot time (or 'console=xencons0' for domain 0), and
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mingetty running on /dev/tty1 (or /dev/xen/cons for domain 0).
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However, domains other than domain 0 do not have access to the
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physical serial line. Instead, their console data is sent to and from
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a control daemon running in domain 0. When properly installed, this
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daemon can be started from the init scripts (e.g., rc.local):
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# /usr/sbin/xend start
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Alternatively, Redhat- and LSB-compatible Linux installations can use
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the provided init.d script. To integrate startup and shutdown of xend
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in such a system, you will need to run a few configuration commands:
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# chkconfig --add xend
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# chkconfig --level 35 xend on
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# chkconfig --level 01246 xend off
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This will avoid the need to run xend manually from rc.local, for example.
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Note that, when a domain is created using xc_dom_create.py, xend MUST
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be running. If everything is set up correctly then xc_dom_create will
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print the local TCP port to which you should connect to perform
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console I/O. A suitable console client is provided by the Python
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module xenctl.console_client: running this module from the command
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line with <host> and <port> parameters will start a terminal
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session. This module is also installed as /usr/bin/xencons, from a
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copy in tools/misc/xencons. For example:
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# xencons localhost 9600
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An alternative to manually running a terminal client is to specify
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'-c' to xc_dom_create.py, or add 'auto_console=True' to the defaults
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file. This will cause xc_dom_create.py to automatically become the
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console terminal after starting the domain.
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