Version used
1.9.26

Describe the bug
root@ubuntu:/tmp# virtnbdbackup -U qemu+ssh://root@192.168.207.167/system --ssh-user root -d kvm_test -l full -o /tmp/back/
[2023-06-28 03:58:57] INFO lib common - printVersion [MainThread]: Version: 1.9.26 Arguments: /usr/local/bin/virtnbdbackup -U qemu+ssh://root@192.168.207.167/system --ssh-user root -d kvm_test -l full -o /tmp/back/
[2023-06-28 03:58:57] INFO root virtnbdbackup - main [MainThread]: Backup level: [full]
root@192.168.207.167's password:
[2023-06-28 03:58:58] INFO root virtnbdbackup - main [MainThread]: Libvirt library version: [8000000]
[2023-06-28 03:58:58] INFO root disktype - Optical [MainThread]: Skipping attached [cdrom] device: [sda].
[2023-06-28 03:58:58] INFO root virtnbdbackup - main [MainThread]: Backup will save [1] attached disks.
[2023-06-28 03:58:58] INFO root virtnbdbackup - main [MainThread]: Concurrent backup processes: [1]
[2023-06-28 03:58:58] INFO root checkpoint - redefine [MainThread]: Loading checkpoint list from: [/tmp/back//checkpoints]
[2023-06-28 03:58:58] INFO root checkpoint - create [MainThread]: Checkpoint handling.
[2023-06-28 03:58:58] INFO root checkpoint - create [MainThread]: Using checkpoint name: [virtnbdbackup.0].
[2023-06-28 03:58:58] INFO root virtnbdbackup - main [MainThread]: Local NBD Endpoint socket: [/var/tmp/virtnbdbackup.3327]
[2023-06-28 03:58:58] INFO root virtnbdbackup - main [MainThread]: Temporary scratch file target directory: [/var/tmp]
[2023-06-28 03:58:58] INFO root virtnbdbackup - startBackupJob [MainThread]: Starting backup job.
[2023-06-28 03:58:58] WARNING fs fs - freeze [MainThread]: Guest agent is not responding: QEMU guest agent is not connected
[2023-06-28 03:58:58] INFO root virtnbdbackup - main [MainThread]: Started backup job with checkpoint, saving information.
[2023-06-28 03:58:58] INFO root checkpoint - backup [MainThread]: Saving checkpoint config to: [/tmp/back//checkpoints/virtnbdbackup.0.xml]
[2023-06-28 03:58:58] INFO nbd client - printVersion [vda]: libnbd version: 1.10.5
[2023-06-28 03:58:58] INFO nbd client - connect [vda]: Waiting until NBD server at [nbd+unix:///vda?socket=/var/tmp/virtnbdbackup.3327] is up.
[2023-06-28 03:58:59] INFO nbd client - connect [vda]: Waiting for NBD Server, Retry: 0
[2023-06-28 03:58:59] ERROR root virtnbdbackup - main [MainThread]: Disk backup failed: [NBD endpoint: [Unix(exportName='vda', metaContext='', backupSocket='/var/tmp/virtnbdbackup.3327', tls=False)]: connection failed: [Unable to connect nbd server: nbd_connect_uri: connect: No such file or directory (ENOENT)]]
[2023-06-28 03:58:59] INFO root virtnbdbackup - main [MainThread]: Backup jobs finished, stopping backup task.
[2023-06-28 03:58:59] INFO root metadata - backupConfig [MainThread]: Saving VM config to: [/tmp/back//vmconfig.virtnbdbackup.0.xml]
[2023-06-28 03:58:59] ERROR libvirtnbdbackup.qemu.command command - run [MainThread]: CMD: qemu-img info /root/kvm/image/ubuntu.qcow2 --output json --force-share
[2023-06-28 03:58:59] WARNING root metadata - backupDiskInfo [MainThread]: Failed to read qcow image info: [Unable to start [qemu-img] error: [qemu-img: Could not open '/root/kvm/image/ubuntu.qcow2': Could not open '/root/kvm/image/ubuntu.qcow2': No such file or directory]]
[2023-06-28 03:58:59] ERROR root virtnbdbackup - main [MainThread]: Error during backup

Expected behavior
A clear and concise description of what you expected to happen.

Hypervisor information:

• OS: ubuntu22.04
• HV type： plain libvirt

Is there something wrong with the way I use it?