Device naming randomness (udev?)

Device naming randomness (udev?)

[Martin J. Bligh]

This PC has 1 ethernet interface, an e1000. Ubuntu Dapper.

On 2.6.14, my e1000 interface appears as eth0.
On 2.6.15 to 2.6.18, my e1000 interface appears as eth1.

In both cases, there are no other ethX interfaces listed in
"ifconfig -a". There are no modules involved, just a static
kernel build.

Is this a bug in udev, or the kernel? I'm presuming udev,
but seems odd it changes over a kernel release boundary.
Any ideas on how I get rid of it? Makes automatic switching
between kernel versions a royal pain in the ass.

M.

Re: Device naming randomness (udev?)

[Björn Steinbrink]

On 2006.12.03 14:39:44 -0800, Martin J. Bligh wrote:
> This PC has 1 ethernet interface, an e1000. Ubuntu Dapper.
> 
> On 2.6.14, my e1000 interface appears as eth0.
> On 2.6.15 to 2.6.18, my e1000 interface appears as eth1.
> 
> In both cases, there are no other ethX interfaces listed in
> "ifconfig -a". There are no modules involved, just a static
> kernel build.
> 
> Is this a bug in udev, or the kernel? I'm presuming udev,
> but seems odd it changes over a kernel release boundary.
> Any ideas on how I get rid of it? Makes automatic switching
> between kernel versions a royal pain in the ass.

Just a wild guess here... Debian's (and I guess Ubuntu's) udev rules
contain a generator for persistent interface name rules. Maybe these
start working with 2.6.15 and thus the switch (ie. the kernel would call
it eth0, but udev renames it to eth1).
The generated rules are written to
/etc/udev/rules.d/z25_persistent-net.rules on Debian, not sure if its
the same for Ubuntu. Editing/removing the rules should fix your problem.

HTH
Björn

Re: Device naming randomness (udev?)

[Greg KH]

On Mon, Dec 04, 2006 at 12:12:06AM +0100, Bj?rn Steinbrink wrote:
> On 2006.12.03 14:39:44 -0800, Martin J. Bligh wrote:
> > This PC has 1 ethernet interface, an e1000. Ubuntu Dapper.
> > 
> > On 2.6.14, my e1000 interface appears as eth0.
> > On 2.6.15 to 2.6.18, my e1000 interface appears as eth1.
> > 
> > In both cases, there are no other ethX interfaces listed in
> > "ifconfig -a". There are no modules involved, just a static
> > kernel build.
> > 
> > Is this a bug in udev, or the kernel? I'm presuming udev,
> > but seems odd it changes over a kernel release boundary.
> > Any ideas on how I get rid of it? Makes automatic switching
> > between kernel versions a royal pain in the ass.
> 
> Just a wild guess here... Debian's (and I guess Ubuntu's) udev rules
> contain a generator for persistent interface name rules. Maybe these
> start working with 2.6.15 and thus the switch (ie. the kernel would call
> it eth0, but udev renames it to eth1).
> The generated rules are written to
> /etc/udev/rules.d/z25_persistent-net.rules on Debian, not sure if its
> the same for Ubuntu. Editing/removing the rules should fix your problem.

Yes, I'd place odds on this one.

Martin, any followup?

thanks,

greg k-h

Re: Device naming randomness (udev?)

[Martin J. Bligh]

Greg KH wrote:
> On Mon, Dec 04, 2006 at 12:12:06AM +0100, Bj?rn Steinbrink wrote:
>> On 2006.12.03 14:39:44 -0800, Martin J. Bligh wrote:
>>> This PC has 1 ethernet interface, an e1000. Ubuntu Dapper.
>>>
>>> On 2.6.14, my e1000 interface appears as eth0.
>>> On 2.6.15 to 2.6.18, my e1000 interface appears as eth1.
>>>
>>> In both cases, there are no other ethX interfaces listed in
>>> "ifconfig -a". There are no modules involved, just a static
>>> kernel build.
>>>
>>> Is this a bug in udev, or the kernel? I'm presuming udev,
>>> but seems odd it changes over a kernel release boundary.
>>> Any ideas on how I get rid of it? Makes automatic switching
>>> between kernel versions a royal pain in the ass.
>> Just a wild guess here... Debian's (and I guess Ubuntu's) udev rules
>> contain a generator for persistent interface name rules. Maybe these
>> start working with 2.6.15 and thus the switch (ie. the kernel would call
>> it eth0, but udev renames it to eth1).
>> The generated rules are written to
>> /etc/udev/rules.d/z25_persistent-net.rules on Debian, not sure if its
>> the same for Ubuntu. Editing/removing the rules should fix your problem.
> 
> Yes, I'd place odds on this one.

Huh. Somehow there was this entry in /etc/iftab:

eth0 mac 00:0d:61:44:90:12 arp 1

But that's not my mac address. Damned if I know how that got there, but
if the persistent rules only work on later kernels, that'd explain it.
And indeed ... removing that entry makes it work more normally.

Thanks for the pointers - most helpful.

M.

Re: Device naming randomness (udev?)

[Tony Breeds]

On Sun, Dec 03, 2006 at 02:39:44PM -0800, Martin J. Bligh wrote:
> This PC has 1 ethernet interface, an e1000. Ubuntu Dapper.
> 
> On 2.6.14, my e1000 interface appears as eth0.
> On 2.6.15 to 2.6.18, my e1000 interface appears as eth1.
> 
> In both cases, there are no other ethX interfaces listed in
> "ifconfig -a". There are no modules involved, just a static
> kernel build.
> 
> Is this a bug in udev, or the kernel? I'm presuming udev,
> but seems odd it changes over a kernel release boundary.
> Any ideas on how I get rid of it? Makes automatic switching
> between kernel versions a royal pain in the ass.

Have a look at /etc/iftab.

Yours Tony

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