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

[John Denker]

Message 2 of 2:  This is easy to use and/or test ifup dummy0 and ifdown
dummy0

You don't need to know the complexities of the motivation for why this
is important;  the test case is very simple.

In the context of the ifupdown package, this requires putting a stanza like this in /etc/network/interfaces or /etc/network/interfaces.d/dummy:
auto dummy0
iface dummy0 inet static
  netmask 255.255.255.255
  address 10.10.2.105

Then the static dummy interface (a) should come up automagically at boot time, and can be further controlled by
:; ifup dummy0
:; ifdown dummy0

Desired behavior:  It should just work.

Observed behavior:
:; ifup dummy0
Cannot find device "dummy0"
Failed to bring up dummy0.

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

See the detailed workaround script attached previously.

FWIW the ifconfig command exhibits all the same misbehavior;  net-tools
and ifupdown are affected in the same way, but remarkably enough the ip
command (from the iproute2 package) is apparently not affected by this
bug.

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

Title:
  ifconfig dummy0 : Device not found

Status in ifupdown package in Ubuntu:
  Incomplete
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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