Set hostname of guest during installation time

Tue May 5 07:26:58 UTC 2020

On 5/5/2020 8:29 AM, Michal Privoznik wrote:
> On 5/5/20 8:11 AM, john doe wrote:
>> On 3/30/2020 4:10 PM, Michal Prívozník wrote:
>>> On 30. 3. 2020 15:26, john doe wrote:
>>>> On 3/30/2020 1:20 PM, Andrea Bolognani wrote:
>>>>> On Mon, 2020-03-30 at 12:04 +0200, Michal Prívozník wrote:
>>>>>> On 27. 3. 2020 20:49, john doe wrote:
>>>>>>> If my understanding is correct, using 'try06' or 'debian' should
>>>>>>> do the
>>>>>>> same thing?
>>>>>>
>>>>>> Yes, that is the idea. However, these plugins were not introduced
>>>>>> at the
>>>>>> same time. I think that especially Debian has delayed libvirt_guest
>>>>>> plugin. You can check if both plugins exist:
>>>>>>
>>>>>> ls /usr/lib64/libnss_libvirt*
>>>>>>
>>>>>> /usr/lib64/libnss_libvirt_guest.so.2
>>>>>> /usr/lib64/libnss_libvirt.so.2
>>>>>
>>>>> Note that paths are different in Debian-based distros, so the correct
>>>>> ones in this case are actually
>>>>>
>>>>>    /lib/x86_64-linux-gnu/libnss_libvirt.so.2
>>>>>    /lib/x86_64-linux-gnu/libnss_libvirt_guest.so.2
>>>>>
>>>>
>>>> I have upgraded that Buster host to Bullseye, so I have now a 6...
>>>> version.
>>>> I have also the above two modules.
>>>>
>>>> I'm still not able to use 'libvirt_guest' though:
>>>>
>>>> --- Guest output (try06):
>>>>
>>>> root at try06:~# cat /etc/hostname
>>>> try06
>>>>
>>>> --- Host output (host):
>>>>
>>>> root at host:# grep hosts: /etc/ns*
>>>> hosts: libvirt_guest
>>>> root at host:# virsh net-dhcp-leases default
>>>>   Expiry Time           MAC address         Protocol   IP address
>>>>     Hostname   Client ID or DUID
>>>> ---------------------------------------------------------------------------------------------------------
>>>>
>>>>   2020-03-30 16:03:41   52:54:00:d4:e6:f0   ipv4 192.168.122.137/24
>>>>    -          -
>>>>
>>>>
>>>> root at host:# getent hosts try06; echo $?
>>>> 2
>>>>
>>>>
>>>> What am I missing?
>>>
>>> Hold on. 'libvirt_guest' NSS plugin is supposed to translate libvirt
>>> names to IP addresses. For instance:
>>>
>>>    virsh start myDomain; ssh myDomain
>>>
>>> The 'libvirt' NSS plugin is supposed to translate hostnames as sent by
>>> guests to IP addresses. These two can be viewed as the following:
>>>
>>> libvirt_guest: virsh domifaddr --source lease $dom
>>>        libvirt: virsh net-dhcp-leases $net | grep $hostname
>>>
>>> And this is where it gets interesting. In your previous e-mails,
>>> net-dhcp-leases (aka 'libvirt' plugin) worked because the guest did send
>>> hostname when doing DHCP. Now it doesn't (see '-' under 'Hostname' in
>>> the output). Therefore, the 'libvirt' NSS plugin won't work.
>>>
>>> And 'libvirt_guest' translates names of guests as seen by libvirt, i.e.
>>> names you pass to virsh commands. These are unrelated to '/etc/hostname'
>>> within guest. But hopefully, you haven't renamed your guest since then
>>> and it is still named 'try06', that is virsh list --all produces 'try06'
>>> in the list. If this is all true, can you share the output of:
>>>
>>>    strace $(which getent) hosts try06
>>>
>>>
>>
>> Thanks to the friendly feedback/support from Michal Privoznik and Andrea
>> Bolognani, I managed to get it working with the below command:
>>
>> virt-install --name=try06 --pxe --os-variant=debian10 --network
>> network=default
>>
>> What I think I mist while trying to implement the recommendation given
>> in here is that, if you change the network by doing 'virsh edit default'
>> the name of the interface in the guest might also change.
>>
>> I don't understand why libvirt_guest won't work if a network bridge is
>> used?
>
> Because interface type='bridge' and type='network' are not the same. The
> libvirt_guest plugin needs a list of MAC addresses because it tries to
> find a match across libvirt domain name -> list of domain's MAC
> addresses -> list of leases. And whenever a domain is started, all its
> interfaces with type='network' will notify the corresponding network and
> the code that handles libvirt networks will dump the MAC address into a
> file for the NSS plugin to use. But, if plain type='bridge' is used then
> all that is done is that the TAP is plugged into the bridge (which
> ensures the connectivity), but does not notify the network which in turn
> means that the MAC dumping code is not run and hence the NSS plugin
> won't find a match.
>

I don't understand why the network can not be notified, could it be a
feature request?

> Is there a reason why you are using interface type='bridge' with the
> default network?
>

I'm just starting with libvirt, so I could be missing something.

Yes, I don't need libvirt touching iptables at all.

In other words, is there a way to be able to use libvirt_guest without
having libvirt interacting with iptables.

>>
>>
>>
>> Also, from (1):
>>
>> "virsh net-dhcp-leases $network
>> where $network iterates through
>> all running network..."
>>
>> If I understand correctly, the below should list all running network:
>>
>> $ virsh net-dhcp-leases $network
>> error: command 'net-dhcp-leases' requires <network> option
>
> This lists DHCP leases for given network. To list all running networks
> you can use 'virsh net-list'.
>

I would suggest rephrasing the above to something along the lines of:

"virsh net-dhcp-leases $network, where '$network' is to be supstituted
by the desired network (E.G, 'default') or use virsh net-list to list
all available network."

>>
>>
>> In my case, I substituted '$network' by 'default'.
>
> It doesn't look like you did, otherwise you would either get leases or
> an error that there is no network named "default".
>
> # virsh net-dhcp-leases
> error: command 'net-dhcp-leases' requires <network> option
> # virsh net-dhcp-leases ""
> error: Failed to get option 'network': Option argument is empty
>
> # virsh net-dhcp-leases default
>   Expiry Time           MAC address         Protocol   IP address
>   Hostname   Client ID or DUID
> ----------------------------------------------------------------------------------------------------------
>
>   2020-05-05 09:01:11   52:54:00:a4:6f:91   ipv4       192.168.122.3/24
>   fedora     01:52:54:00:a4:6f:91
>

Thanks for this.

--
John Doe