[Bug 1828749] Re: ifconfig dummy0 : Device not found

[Paride Legovini]

Thanks for sharing your findings. What you found out is indeed
interesting, however I'm not sure you can say the change happened in
modprobe, as you are using two different kernel versions. Perhaps insmod
and modprobe always behaved differently, and what changed is what the
kernel does.

Your suggestion for a more robust handling of dummy interfaces makes
sense, however even if this were done I don't think your use case alone
would be enough to justify an upgrade in Bionic (a so-called Stable
Release Upgrade). On the other side, newer releases of Ubuntu are
switching from ifupdown to netplan, so at this point it is unlikely that
any active work will be put into ifupdown unless there is a compelling
reason to do so.

Should a wider-impact use case come up then we will certainly re-
evaluate the importance of this report.

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https://bugs.launchpad.net/bugs/1828749

Title:
  ifconfig dummy0 : Device not found

Status in ifupdown package in Ubuntu:
  New
Status in net-tools package in Ubuntu:
  New

Bug description:
  Desired behavior:
    The ifconfig command should be able to deal with the
    dummy device.  This worked fine until recently.

  Observed behavior:
    :; ifconfig dummy0
    dummy0: error fetching interface information: Device not found

    This problem appeared when I upgraded to bionic.

  Highly informative workaround:
    :; ip link add dummy0 type dummy
    That command works, and makes the problem go away permanently.
    The ifconfig command works fine after that.
    The ifup and ifdown commands also work fine after that.

    For convenient debugging, you can use the command:
    :; ip link del dummy0 type dummy
    which makes the problem come back.
    You can also experiment with dummy1 et cetera.

  Package ownership issues:
    Compare: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=909204
    That report was filed against ippusbxd, which is almost certainly
    not the relevant package.

    For that matter, I have no idea whether the root cause is in the
    net-tools package or the kernel networking stack.  All I know is
    the ip command plays nicely with the kernel while the ifconfig
    command does not.

  
  Notes:
    The kernel module for the dummy interface is preloaded in
    all situations described here.  That's not the issue.

    An apport file is attached, to describe the environment.
    Also, since you asked:

    :; apt-cache policy net-tools
  net-tools:
    Installed: 1.60-26ubuntu1
    Candidate: 1.60-26ubuntu1
    Version table:
   *** 1.60-26ubuntu1 500
          500 http://ubuntu.cs.utah.edu/ubuntu xenial/main amd64 Packages
          100 /var/lib/dpkg/status

    :; lsb_release -rd
    Description:    Ubuntu 16.04.6 LTS
    Release:        16.04

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