I'm using qemu-nbd to setup the device with an offset into the image. Using libguestfs version 1.21.22 Code for adding the drive: char *server[] = { "localhost:3000", NULL }; if (guestfs_add_drive_opts (g, "" /* export name - see below */, GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw", GUESTFS_ADD_DRIVE_OPTS_PROTOCOL, "nbd", GUESTFS_ADD_DRIVE_OPTS_SERVER, server, -1) Here is some of the stdout. A mix of libguestfs and qemu-nbd messages. qemu-nbd -v -n -o 77824 -t -p 3000 -c /dev/nbd0 /home/skippy/mnt/mnt0/win7x64amdHP.vdi NBD device /dev/nbd0 is now connected to /home/skippy/mnt/mnt0/win7x64amdHP.vdi libguestfs: launch: attach-method=appliance libguestfs: launch: tmpdir=/tmp/libguestfsLFMzZI libguestfs: launch: umask=0022 libguestfs: launch: euid=0 libguestfs: [00000ms] begin testing qemu features libguestfs: command: run: /usr/bin/qemu-system-x86_64 libguestfs: command: run: \ -nographic libguestfs: command: run: \ -help libguestfs: command: run: /usr/bin/qemu-system-x86_64 libguestfs: command: run: \ -nographic libguestfs: command: run: \ -version libguestfs: qemu version 1.2 libguestfs: command: run: /usr/bin/qemu-system-x86_64 libguestfs: command: run: \ -nographic libguestfs: command: run: \ -machine accel=kvm:tcg libguestfs: command: run: \ -device ? libguestfs: [00131ms] finished testing qemu features \ libguestfs: child_cleanup: 0xbc4ba0: child process died libguestfs: sending SIGTERM to process 23981 libguestfs: closing guestfs handle 0xbc4ba0 (state 0) libguestfs: command: run: rm libguestfs: command: run: \ -rf /tmp/libguestfsLFMzZI skippy@DaneelOlivaw:~/tmp/bin$ /build/buildd/qemu-kvm-1.2.0+noroms/nbd.c:nbd_trip():L835: From: 18446744073709551104, Len: 0, Size: 20003880960, Offset: 77824 /build/buildd/qemu-kvm-1.2.0+noroms/nbd.c:nbd_trip():L836: requested operation past EOF--bad client? /build/buildd/qemu-kvm-1.2.0+noroms/nbd.c:nbd_receive_request():L516: read failed So I peppered some fprintfs in launch-appliance.c to try and narrow down the problem. Just below the comment: * does not mean the daemon is up until we read the * GUESTFS_LAUNCH_FLAG below. Failures in qemu startup can still Is the call where it fails: r = guestfs___recv_from_daemon (g, &size, &buf); r is -1 and size is zero How can I debug this problem further? I suppose I could build/debug the qemu side of this process... -Skippy