Friday, 25 September 2015

Re: Proposal v2: enable stateless persistant network interface names

Hey Jason,

Jason Gerard DeRose [2015-09-24 15:46 -0600]:
> Is it possible to turn this off, revert to (non persistent) eth0, eth1, etc,
> names?

Yes, see /usr/share/doc/udev/README.Debian.gz . You can either turn it
off globally (boot with net.ifnames=0 or create an empty
/etc/udev/rules.d/80-net-setup-link.rules), or change the name of
individual ethernet interfaces.

Note that this will then only work reliably if you have exactly one
ethernet card.

> The place where I've gotten stuck with this is when PXE booting with a
> rootfs exported over NFS.
>
> In this case you need to specify, eg, DEVICE=eth0, in your initramfs.conf
> when building the initrd image that you're going PXE boot with. But this is
> very problematic unless you can easily know in advance what the name of the
> first NIC will be, unless it will be the same NIC name across a range of
> arbitrary hardware.

Hardcoding DEVICE=eth0 is rather pointless. If there is only one NIC
there is nothing to select, and if you have multiple cards then this
still doesn't select which one you actually want. I guess this is a
bug/mis-design in initramfs-tools, so I'm not sure you can easily fix
this properly.

I guess an initrd with PXE enabled should just try to boot from any
found ethernet card by default, and if you explicitly give it a device
name (or properties) use that.

> Because we've needed to count on the first NIC being named eth0, we've
> always removed the biosdevname package when building this server
> environment.

So disabling net.ifnames would be the equivalent workaround.

But that's what it really is -- a workaround. Either you don't care
about which device you boot from, then it's pointless to specify a
hardcoded "eth0" value -- or you do care, then you need to have a
better way of identifying a device than the randomly assigned kernel
name (which doesn't help you at all).

Thanks,

Martin

--
Martin Pitt | http://www.piware.de
Ubuntu Developer (www.ubuntu.com) | Debian Developer (www.debian.org)

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