[Bug 1307429] Re: Existing allow-hotplug devices do not come up

[Benjamin Drung]

The difference between auto and allow-hotplug is the behaviour on boot.
When a device is marked as auto, it will be tried to be activated on
boot and the boot will wait for the device to come up. Following
interface config

-----
auto lo
iface lo inet loopback
auto eth0
iface eth0 inet dhcp
auto eth1
iface eth1 inet dhcp
auto eth2
iface eth2 inet dhcp
-----

will cause these plymouth output:

-----
waiting for network configuration
waiting an additional 60 seconds for network configuration
-----

So allow-hotplug is not equivalent to auto and is bug which should be
fixed in a SRU. Side note: allow-hotplug works on Debian.

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https://bugs.launchpad.net/bugs/1307429

Title:
  Existing allow-hotplug devices do not come up

Status in “ifupdown” package in Ubuntu:
  Triaged

Bug description:
  Devices that are listed with allow-hotplug in /etc/network/interfaces
  do not come up when they are hotplugged. "ip addr" shows that these
  devices are down.

  Steps to reproduce:

  1) Install Ubuntu 12.04, 13.10, or 14.04 in a virtual machine (e.g. with libvirt) with one network device.
  2) Modify /etc/network/interfaces to

  auto lo
  iface lo inet loopback
  allow-hotplug eth0
  iface eth0 inet dhcp
  allow-hotplug eth1
  iface eth1 inet dhcp
  allow-hotplug eth2
  iface eth2 inet dhcp

  3) Boot your virtual machine.
  4) Type "ip addr" to show your network devices. It should show eth0 which should be up (but isn't)
  5) Add/Hotplug one NIC to your virtual machine.
  6) "ip addr" should show that eth1 is up too (but isn't)

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