Public bug reported: On Ubuntu 12.10 through Ubuntu 16.04, something like this worked with 100% reliability in my experience:
sudo modprobe nbd sudo qemu-nbd -c /dev/nbd0 /my/vm/image.qcow2 sudo mount /dev/nbd0p1 /mnt But on Yakkety, this *almost* always fails because the /dev/nbd0p1 device doesn't exist by the time the `sudo mount /dev/nbd0p1 /mnt` command is run. I found an existing Debian bug about this: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=824553 Unfortunately, I feel the bug reporter got the brush off there, but I can confirm that `qemu-nbd` previously worked exactly as the bug reporter claims (on Ubuntu anyway, not sure about Debian). I have automated tooling that has done this exact thing many thousands of times on Ubuntu 12.10 through 16.04 without issue. Although in defense of the Debian maintainer, my hunch is this behavior change likely isn't the result of changes in the `qemu-img` package itself. A curiosity of note is that although this usually fails on Yakkety, it did work for me a few times (in my testing thus far, I'd say it succeeds less than 5% of the time). I haven't yet found a way to reproduce these successful cases, nor have I yet spotted any pattern in the cases in which it works vs. cases in which it doesn't work. On Yakkety I can *mostly* work-around this by calling `sudo partprobe /dev/nbd0` prior to trying to mount the device: sudo modprobe nbd sudo qemu-nbd -c /dev/nbd0 /my/vm/image.qcow2 sudo partprobe /dev/nbd0 sudo mount /dev/nbd0p1 /mnt At first I thought this was a 100% reliable solution on Yakkety, but it still sometimes fails. I haven't had as much time testing this yet, but I'd say it probably succeeds 80% of the time or so, fails the remaining 20%. I hate to say it, but on the surface this feels like a systemd bug as I've encountered systemd + qemu-nbd problems in the past: https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1435428 Plus whenever I hear of "weird problems mounting or unmounting devices" plus "non-determinism"... systemd comes to mind :P So my hunch is this isn't actually a `qemu-img` bug. My best guess is systemd, but it could also be the Linux 4.4 vs 4.8 kernel or something else I haven't thought of. Still, without stronger evidence, to me it seems `qemu-img` is the best package to initially file this bug against. Also, I'm not yet sure how best to debug this, but the most helpful logging I've found thus far is in /var/log/syslog. Thanks! ProblemType: Bug DistroRelease: Ubuntu 16.10 Package: qemu-utils 1:2.6.1+dfsg-0ubuntu5 ProcVersionSignature: Ubuntu 4.8.0-17.19-generic 4.8.0-rc7 Uname: Linux 4.8.0-17-generic x86_64 NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia ApportVersion: 2.20.3-0ubuntu7 Architecture: amd64 CurrentDesktop: Unity:Unity7 Date: Tue Oct 4 10:44:58 2016 KvmCmdLine: COMMAND STAT EUID RUID PID PPID %CPU COMMAND kvm-irqfd-clean S< 0 0 18420 2 0.0 [kvm-irqfd-clean] MachineType: System76, Inc. Serval WS ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.8.0-17-generic.efi.signed root=UUID=4b57bce3-eed0-426b-adfe-4f7a834e2ddf ro net.ifnames=0 quiet splash vt.handoff=7 SourcePackage: qemu UpgradeStatus: Upgraded to yakkety on 2016-10-03 (0 days ago) dmi.bios.date: 06/09/2015 dmi.bios.vendor: American Megatrends Inc. dmi.bios.version: 1.03.03RSY2 dmi.board.asset.tag: Tag 12345 dmi.board.name: Serval WS dmi.board.vendor: System76, Inc. dmi.board.version: serw8-17g dmi.chassis.asset.tag: No Asset Tag dmi.chassis.type: 9 dmi.chassis.vendor: System76, Inc. dmi.chassis.version: Serval WS dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr1.03.03RSY2:bd06/09/2015:svnSystem76,Inc.:pnServalWS:pvrserw8-17g:rvnSystem76,Inc.:rnServalWS:rvrserw8-17g:cvnSystem76,Inc.:ct9:cvrServalWS: dmi.product.name: Serval WS dmi.product.version: serw8-17g dmi.sys.vendor: System76, Inc. ** Affects: qemu (Ubuntu) Importance: Undecided Status: New ** Affects: qemu (Debian) Importance: Unknown Status: Unknown ** Tags: amd64 apport-bug yakkety ** Bug watch added: Debian Bug tracker #824553 http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=824553 ** Also affects: qemu (Debian) via http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=824553 Importance: Unknown Status: Unknown -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1630341 Title: yakkety: behavior change in `qemu-nbd -c $DEV $FILENAME`: doesn't automatically create partion devices To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1630341/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
