FAQ
I want to give my clients access to their Xen domU consoles using VNC. This works great using vfb device configured as type=vnc.

However I have 2 problems:

* I can't figure out how I can add a vfb device to a running domain without restarting it (I have 100+ domU's I want to enable this on, and want to avoid restarting them all if possible)

* Related, I can't figure out how I can change the VNC password without restarting the domU, as the password is specified in the vfb config.

Is what I am trying to do possible? How?

In case it matters: # xm info
host : <my.supersecret.hostname>
release : 2.6.18-194.26.1.el5xen
version : #1 SMP Tue Nov 9 13:35:30 EST 2010
machine : x86_64
nr_cpus : 4
nr_nodes : 1
sockets_per_node : 1
cores_per_socket : 4
threads_per_core : 1
cpu_mhz : 2394
hw_caps : bfebfbff:28100800:00000000:00000140:0098e3fd:00000000:00000001
total_memory : 24566
free_memory : 8317
node_to_cpu : node0:0-3
xen_major : 3
xen_minor : 1
xen_extra : .2-194.26.1.el5
xen_caps : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32 hvm-3.0-x86_32p hvm-3.0-x86_64
xen_pagesize : 4096
platform_params : virt_start=0xffff800000000000
xen_changeset : unavailable
cc_compiler : gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)
cc_compile_by : mockbuild
cc_compile_domain : centos.org
cc_compile_date : Tue Nov 9 12:45:24 EST 2010
xend_config_format : 2


Thanks in advance

--
Chris Wik
Anu Internet Services Ltd

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  • Pasi Kärkkäinen at Jan 15, 2011 at 6:12 pm

    On Tue, Jan 11, 2011 at 01:16:28PM +0100, Chris Wik wrote:
    I want to give my clients access to their Xen domU consoles using VNC. This works great using vfb device configured as type=vnc.

    However I have 2 problems:

    * I can't figure out how I can add a vfb device to a running domain without restarting it (I have 100+ domU's I want to enable this on, and want to avoid restarting them all if possible)
    I've never heard about vfb hotplug..

    * Related, I can't figure out how I can change the VNC password without restarting the domU, as the password is specified in the vfb config.

    Is what I am trying to do possible? How?
    I wonder if the password is stored inside the qemu-dm process (vnc server),
    or in xenstore..

    If it's in xenstore then it's easy to change it.

    -- Pasi
  • Chris Wik at Jan 15, 2011 at 7:22 pm

    On 16.01.2011, at 00:12, Pasi K?rkk?inen wrote:

    * Related, I can't figure out how I can change the VNC password without restarting the domU, as the password is specified in the vfb config.

    Is what I am trying to do possible? How?
    I wonder if the password is stored inside the qemu-dm process (vnc server),
    or in xenstore..

    If it's in xenstore then it's easy to change it.

    Thanks for the tip, I never looked into xenstore before.

    So I found that the vncpass is stored in xenstore:

    # xenstore-read /local/domain/0/backend/vfb/<domain id>/0/vncpasswd
    -> test123

    # xenstore-write /local/domain/0/backend/vfb/19/0/vncpasswd test234

    # xenstore-read /local/domain/0/backend/vfb/<domain id>/0/vncpasswd
    -> test234

    OK, so I can read and write the password. However, when I open a VNC connection, the new password is not in effect, instead the old one is still valid.

    I noticed the qemu-dm process which looks like it might be responsible for setting up the vnc server:

    # ps ax | grep vnc
    ,,,
    12301 pts/0 Sl 0:00 /usr/lib64/xen/bin/qemu-dm -M xenpv -d <domain id> -domain-name <domain name> -vnc 0.0.0.0:<vnc port>,password -k en-us

    I tried sending this pid a HUP signal to see if it would reload the password, but instead it just died. Do you think I'm on the right track here? Any further suggestions would be very much appreciated.

    Chris

    --
    Chris Wik
    Anu Internet Services Ltd
  • Pasi Kärkkäinen at Jan 18, 2011 at 8:35 am

    On Sun, Jan 16, 2011 at 01:22:30AM +0100, Chris Wik wrote:
    On 16.01.2011, at 00:12, Pasi K?rkk?inen wrote:

    * Related, I can't figure out how I can change the VNC password without restarting the domU, as the password is specified in the vfb config.

    Is what I am trying to do possible? How?
    I wonder if the password is stored inside the qemu-dm process (vnc server),
    or in xenstore..

    If it's in xenstore then it's easy to change it.

    Thanks for the tip, I never looked into xenstore before.

    So I found that the vncpass is stored in xenstore:

    # xenstore-read /local/domain/0/backend/vfb/<domain id>/0/vncpasswd
    -> test123

    # xenstore-write /local/domain/0/backend/vfb/19/0/vncpasswd test234

    # xenstore-read /local/domain/0/backend/vfb/<domain id>/0/vncpasswd
    -> test234

    OK, so I can read and write the password. However, when I open a VNC connection, the new password is not in effect, instead the old one is still valid.

    I noticed the qemu-dm process which looks like it might be responsible for setting up the vnc server:

    # ps ax | grep vnc
    ,,,
    12301 pts/0 Sl 0:00 /usr/lib64/xen/bin/qemu-dm -M xenpv -d <domain id> -domain-name <domain name> -vnc 0.0.0.0:<vnc port>,password -k en-us

    I tried sending this pid a HUP signal to see if it would reload the password, but instead it just died. Do you think I'm on the right track here? Any further suggestions would be very much appreciated.
    Sorry, I don't know more about this..
    Try reading xen qemu-dm sources?

    -- Pasi

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postedJan 11, '11 at 7:16a
activeJan 18, '11 at 8:35a
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