hostnamectl; # tested on
Operating System: Debian GNU/Linux 12 (bookworm) 
Kernel: Linux 6.1.0-53-amd64
Architecture: x86-64

su - root
modprobe nbd max_part=16

# create thin provision new kvm harddisk file of size 1024GBytes
qemu-img create -f qcow2 /home/user/vms/transfer_host_guest.qcow2.qcow2 1024G

# connect to kvm host
qemu-nbd --connect=/dev/nbd0 /home/user/vms/transfer_host_guest.qcow2.qcow2
udevadm settle
lsblk /dev/nbd0
mkdir /media/user/nbd0
mount /dev/nbd0 /media/user/nbd0/
mkfs.ext4 -L "transfer" /dev/nbd0
mount /dev/nbd0 /media/user/nbd0/
chown -R user:user /media/user/nbd0/

# write files
cp -rv /home/user/thisfile /media/user/nbd0/
sync

# unmount and discconect from host
umount /media/user/nbd0/
qemu-nbd --disconnect /dev/nbd0

# attach to running vm
virsh attach-disk debian13_packettracer /home/user/vms/transfer_host_guest.qcow2.qcow2 vdb --targetbus virtio --driver qemu --subdriver qcow2 --persistent

if the spice tools are installed, clipboard sharing between host and guest (copy & pasting text and even images (!)) should (!) work 😀

What is not working virtualbox-easy-style (yet) is easy-host-to-guest-and-vice-versa-file-transfer (which IS VERY ANNOYING (RedHat are you listening? no?) having to “hack around” the problem with iso images)

hostnamectl; # tested with
  Operating System: Debian GNU/Linux 11 (bullseye)
            Kernel: Linux 5.10.0-22-amd64
      Architecture: x86-64

two possibilities:

  • first:
    • generate a iso image (but this is a bit cumbersome)
    • su - root
apt update && apt install genisoimage
genisoimage -o name-of-iso-file.iso ./add-this-file-to-the-iso.tar.gz
# if more than 4GB needs to be transfered
genisoimage -allow-limited-size -l -J -r -iso-level 3 -o <output.iso> <source file or directory>
# or
mkisofs -allow-limited-size -l -J -r -iso-level 3 -o <output.iso> <source file or directory>
    • then mount iso image via virt-manager
      • powerdown vm
      • edit vm details
      • add storage device DVD
      • click on new storage device and select just created image.iso
  •  second: (also not very conveniant as the user usually wants to exchange files online not offline, RedHat are you listening? no?)
    • shutdown the kvm guest
    • mount the qcow2 into the host filesystem like this:
  • third: setup a vm as samba file server (only on trusted networks! currently the best option for online file transfer)
# to mount a kvm.qcow2 harddisk image
su - root
modprobe nbd max_part=63
qemu-nbd -c /dev/nbd0 /home/user/vms/kvm/harddisk.image.qcow2

# non-gui way
# find mountable partitions

# with these two very helpful overview-harddisk alias no problem
# run this
alias harddisks='lsblk -o '\''NAME,MAJ:MIN,RM,SIZE,RO,FSTYPE,MOUNTPOINT,UUID'\'''
# run that
alias loop_df='while true; do (clear; echo '\''===== hostname:'\''; hostnamectl; echo '\''===== looped harddisk info '\''; datum; dmesg|tail -n20; echo '\''===== where is what'\''; harddisks; echo '\''===== harddisk usage'\''; df -Th;) ; sleep 1 ; done'
# then run
loop_df

# mount the root-partition of the guest
mount /dev/nbd0p1 /media/user/kvm_guest_mount/

# transfer files, then umount when done
umount /dev/nbd0p1

# gui-way: open up a filemanager (caja etc.)
# and click on the newly available virtual harddisk
# it will ask for password to mount it 

# to umount a kvm.qcow2 harddisk image
qemu-nbd -d /dev/nbd0

manpages:

qemu-nbd.man.txt

virt-manager.man.txt

liked this article?

  • only together we can create a truly free world
  • plz support dwaves to keep it up & running!
  • (yes the info on the internet is (mostly) free but beer is still not free (still have to work on that))
  • really really hate advertisement
  • contribute: whenever a solution was found, blog about it for others to find!
  • talk about, recommend & link to this blog and articles
  • thanks to all who contribute!
admin