How to run KVM from LIVE CD in Ubuntu?

Question

ubuntu

To reduce the size of the KVM image, it was necessary to run it from another Ubuntu 20.04 live image . I did the
following on the host machine:

like this

<disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <source file='/home/folder1/subfolder1/ubuntu-20.04.4-live-server-amd64.iso'/>
      <target dev='hdc' bus='ide'/>
      <readonly/>
      <address type='drive' controller='0' bus='1' target='0' unit='0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/home/folder1/subfolder2/main_dev.img'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </disk>

3. Executed virsh start vmname

KVM started up, but does not let you into its console via SSH. I tried the old login and password from KVM, host and default (ubuntu login and empty password). Doesn't let me in with the comment Permission denied, please try again. When starting from the old image, everything works as expected. Through the host console also does not let. virsh console vmname shows Connected to domain vmname Escape character is ^]

Why does this happen and how can I fix it?