Troubleshooting

Here are some things to check if there are problems running syzkaller.

• Check that QEMU can successfully boot the virtual machine. For example, if IMAGE is set to the VM's disk image (as per the image config value) and KERNEL is set to the test kernel (as per the kernel config value) then something like the following command should start the VM successfully:

  qemu-system-x86_64 -hda $IMAGE -m 256 -net nic -net user,host=10.0.2.10,hostfwd=tcp::23505-:22 -enable-kvm -kernel $KERNEL -append root=/dev/sda
  

• Check that inbound SSH to the running virtual machine works. For example, with a VM running and with SSHKEY set to the SSH identity (as per the sshkey config value) the following command should connect:

  ssh -i $SSHKEY -p 23505 root@localhost
  

• If you are having SSH difficulties, make sure your kernel configuration has networking enabled. Sometimes defconfig errs minimalistic and omits the following necessary options:

  CONFIG_VIRTIO_NET=y
  CONFIG_E1000=y
  CONFIG_E1000E=y
  

• If the virtual machine reports that it has “Failed to start Raise network interfaces” or (which is a consequence of that) syzkaller is unable to connect to the virtual machines, try to disable the Predictable Network Interface Names mechanism. There are two ways to achieve this:

  • Add the following two lines to the kernel configuration file and recompile the kernel.

    CONFIG_CMDLINE_BOOL=y
    CONFIG_CMDLINE="net.ifnames=0"
    

  • Add the following line to the VM's properties inside the syzkaller manager configuration:

    "cmdline": "net.ifnames=0"
    

    The resulting configuration may look like this:

    {
      "target": "linux/amd64",
      "http": "127.0.0.1:56741",
      "workdir": "$GOPATH/src/github.com/google/syzkaller/workdir",
      "kernel_obj": "$KERNEL",
      "image": "$IMAGE/bullseye.img",
      "sshkey": "$IMAGE/bullseye.id_rsa",
      "syzkaller": "$GOPATH/src/github.com/google/syzkaller",
      "procs": 8,
      "type": "qemu",
      "vm": {
          "count": 4,
          "kernel": "$KERNEL/arch/x86/boot/bzImage",
          "cmdline": "net.ifnames=0",
          "cpu": 2,
          "mem": 2048
      }
    }
    

    This is, however, not guaranteed to work across all virtualization technologies.

• Check that the CONFIG_KCOV option is available inside the VM:

  • ls /sys/kernel/debug # Check debugfs mounted
  • ls /sys/kernel/debug/kcov # Check kcov enabled
  • Build the test program from Documentation/kcov.txt and run it inside the VM.

• Check that debug information (from the CONFIG_DEBUG_INFO option) is available

  • Pass the hex output from the kcov test program to addr2line -a -i -f -e $VMLINUX (where VMLINUX is the vmlinux file, as per the kernel_obj config value), to confirm that symbols for the kernel are available.

Also see this for generic troubleshooting advice.

If none of the above helps, file a bug on the bug tracker or ask us directly on the syzkaller@googlegroups.com mailing list. Please include syzkaller commit id that you use and syz-manager output with -debug flag enabled if applicable.