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

[John Denker]

Here is better evidence.
Just now I ran the experiment using same kernel version, 4.19.42,
as in the xenial experiment reported above.

My conclusions are unchanged.  The newly-introduced incompatible
and inconsistent behavior depends on the modprobe release, not
on the kernel release.  I knew this to be true, as stated
previously, but now we have clearer evidence on the record.


** Attachment added: "bionic: (same kernel) insmod and modprobe behave differently"
   https://bugs.launchpad.net/ubuntu/+source/net-tools/+bug/1828749/+attachment/5265060/+files/dummy-beaver.logg

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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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