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Re: Set hostname of guest during installation time



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 try06:~# cat /etc/hostname
try06

--- Host output (host):

root host:# grep hosts: /etc/ns*
hosts: libvirt_guest
root 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 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?



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


In my case, I substituted '$network' by 'default'.


1)  https://libvirt.org/nss.html#Internals


--
John Doe



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