Using biosdevname by default?

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Using biosdevname by default?

Colin Watson
Dell has asked for biosdevname to be enabled by default on new Ubuntu
installations on Dell PowerEdge servers:

  https://bugs.launchpad.net/ubuntu/+source/biosdevname/+bug/891258

I do not feel that this is a decision I can take on my own, and would
like to seek guidance from the good folks on these lists.

For those unfamiliar with biosdevname, it's a udev helper intended to
handle the problem of unstable network device enumeration ordering by
mapping them into different namespaces according to BIOS-provided naming
information.  More information can be found here:

  http://linux.dell.com/biosdevname/
  http://manpages.ubuntu.com/biosdevname

This is supported on an opt-in basis from Ubuntu 11.04 on (modulo a bug
in 11.04 to the effect that it didn't work with a separate /usr, fixed
in 11.10) by passing the "biosdevname=1" kernel parameter when starting
the installer.


There are certainly some advantages to enabling biosdevname by default.
On systems that support it, it makes it somewhat easier to write scripts
that predictably apply to a certain interface without having to mess
around with looking up interfaces by MAC address.

However, I have a few concerns about enabling this by default.  Firstly,
I think it is in general unwise to make this kind of change for a single
class of machine, at least for Ubuntu itself as opposed to
vendor-specific builds.  The effect of doing that is to divide our
testing efforts, so that tests of relevant functionality on one class of
machine can no longer be presumed to be valid for others.  This usually
ends up being to the detriment of everyone: Dell servers would no longer
be able to take advantage of the testing we do on other classes of
system.

Of course, not many other systems support biosdevname anyway; HP
ProLiants are explicitly handled in the biosdevname source, but for many
systems, including at least kvm but many real machines as well,
biosdevname will just leave the kernel-provided interface names in
place.  (Even if biosdevname supported no non-Dell systems right now,
I'd still be of the opinion that we should be as consistent about it as
we can on the basis that other BIOSes might add support at some point in
the next five years.)

Secondly, while as I said above I agree that enabling biosdevname solves
some problems, it seems likely that this change will cause problems of
its own.  For example, any software that needs to know about network
interfaces (let's say it listens on a particular interface) might well
default to eth0; this will break on many wireless-only systems and
require manual configuration, but if it's not the sort of thing that you
use on a laptop, many users might not previously have noticed.  Using
biosdevname by default would extend these problems to many server-class
machines out of the box.  While anything like this is certainly a bug
already, with the new scheme we'd *have* to fix everything like that and
it'd be easy to miss something.  The question of whether you see this as
an opportunity to expose existing bugs or as a risk rather depends on
your point of view. :-)

Still, I'm not typically working in environments where unstable network
device naming causes me any problems, so I tend to see the downsides
rather than the upsides.  I'd like to hear from people who do suffer
from this kind of problem, as well as from the server team who would
presumably be at the sharp end either way.

Thanks,

--
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Re: Using biosdevname by default?

Stéphane Graber-2
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On 01/31/2012 09:29 AM, Colin Watson wrote:

> Dell has asked for biosdevname to be enabled by default on new
> Ubuntu installations on Dell PowerEdge servers:
>
> https://bugs.launchpad.net/ubuntu/+source/biosdevname/+bug/891258
>
> I do not feel that this is a decision I can take on my own, and
> would like to seek guidance from the good folks on these lists.
>
> For those unfamiliar with biosdevname, it's a udev helper intended
> to handle the problem of unstable network device enumeration
> ordering by mapping them into different namespaces according to
> BIOS-provided naming information.  More information can be found
> here:
>
> http://linux.dell.com/biosdevname/ 
> http://manpages.ubuntu.com/biosdevname
>
> This is supported on an opt-in basis from Ubuntu 11.04 on (modulo a
> bug in 11.04 to the effect that it didn't work with a separate
> /usr, fixed in 11.10) by passing the "biosdevname=1" kernel
> parameter when starting the installer.
>
>
> There are certainly some advantages to enabling biosdevname by
> default. On systems that support it, it makes it somewhat easier to
> write scripts that predictably apply to a certain interface without
> having to mess around with looking up interfaces by MAC address.
>
> However, I have a few concerns about enabling this by default.
> Firstly, I think it is in general unwise to make this kind of
> change for a single class of machine, at least for Ubuntu itself as
> opposed to vendor-specific builds.  The effect of doing that is to
> divide our testing efforts, so that tests of relevant functionality
> on one class of machine can no longer be presumed to be valid for
> others.  This usually ends up being to the detriment of everyone:
> Dell servers would no longer be able to take advantage of the
> testing we do on other classes of system.
>
> Of course, not many other systems support biosdevname anyway; HP
> ProLiants are explicitly handled in the biosdevname source, but for
> many systems, including at least kvm but many real machines as
> well, biosdevname will just leave the kernel-provided interface
> names in place.  (Even if biosdevname supported no non-Dell systems
> right now, I'd still be of the opinion that we should be as
> consistent about it as we can on the basis that other BIOSes might
> add support at some point in the next five years.)
>
> Secondly, while as I said above I agree that enabling biosdevname
> solves some problems, it seems likely that this change will cause
> problems of its own.  For example, any software that needs to know
> about network interfaces (let's say it listens on a particular
> interface) might well default to eth0; this will break on many
> wireless-only systems and require manual configuration, but if it's
> not the sort of thing that you use on a laptop, many users might
> not previously have noticed.  Using biosdevname by default would
> extend these problems to many server-class machines out of the box.
> While anything like this is certainly a bug already, with the new
> scheme we'd *have* to fix everything like that and it'd be easy to
> miss something.  The question of whether you see this as an
> opportunity to expose existing bugs or as a risk rather depends on
> your point of view. :-)
>
> Still, I'm not typically working in environments where unstable
> network device naming causes me any problems, so I tend to see the
> downsides rather than the upsides.  I'd like to hear from people
> who do suffer from this kind of problem, as well as from the server
> team who would presumably be at the sharp end either way.
>
> Thanks,
>

Hello,

As you know I've spent quite a bit of time looking at and fixing a
bunch of network related packages and hooks lately.

One thing I noticed in quite a few places is the use of wildcard like
"eth*.*|bond*.*|wlan*.*" to match any ethernet network interface on
which to create a VLAN.

Using em* or pci* will break these scripts and possibly much more than
the ones I found with a quick grep on my system.

If we are to do it, this will need extensive testing on systems where
 biosdevname would rename interfaces, including making sure we don't
have any race condition in udev/upstart as we use the udev events to
trigger interface configuration through upstart and through a bunch of
udev hooks (vlan, bridging, ...).

I personally find this change risky for 12.04, I agree the hardcoded
use of eth* and similar are hacks that we should get rid of, but I
doubt we have the resources or time to check and fix the whole archive
in time for 12.04.

It's the kind of change I'd be happy for us to do in early 12.10,
making it clear to all affected teams that this bit changed and to
look for bugs.
I'm quite happy at how stable networking is now in 12.04, it'd be a
shame to break it now by turning on something like biosdevname.

- --
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com
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Re: Using biosdevname by default?

Martin Pitt-4
In reply to this post by Colin Watson
Colin Watson [2012-01-31 14:29 +0000]:
> There are certainly some advantages to enabling biosdevname by default.
> On systems that support it, it makes it somewhat easier to write scripts
> that predictably apply to a certain interface without having to mess
> around with looking up interfaces by MAC address.

I agree that in many situations where you work with multiple
interfaces, stable names would be much preferrable.

> [...]
> Secondly, while as I said above I agree that enabling biosdevname solves
> some problems, it seems likely that this change will cause problems of
> its own.  For example, any software that needs to know about network
> interfaces (let's say it listens on a particular interface) might well
> default to eth0

Stephane confirmed that this is an actual problem in his reply.

This situation has a striking similarity with stable names for block,
sound, and input devices. There was a time when the "classic" names
like hda/sda went away entirely, but this situation never lasted very
long because of pretty much exactly this problem: too much software
making hardcoded assumptions about device names.

That's why the current policy eventually distilled itself: it is
actively wrong, and now even unsupported by udev to rename devices, so
schemas like "sd[a-z][0-9]"  or input/event* will always continue to
work. Instead, the only thing you can and should do is to create
aliases in the form of symlinks (/dev/disks/by-uuid/,
/dev/input/by-id/, etc.)

Now, unfortunately network devices have always been special in that
they are not proper character devices, so symlinks don't work.  But as
the kernel supports renaming devices, is there any way of providing
the same devices under two names, i. e. adding aliases instead of
ifrename? interfaces(5) already supports mappings and renames, so from
my naive POV it seems this shouldn't be too hard to get a concept of
aliases? Perhaps even the Dell folks would be interested in this, as
it would remove the main blocker for adoption?

If we can get this to work, then I see no reason to not introduce
biosdevname, as it would not break any existing setup, local
configuration, or hardcoded assumption.

Thanks,

Martin
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Re: Using biosdevname by default?

Scott Ritchie
In reply to this post by Stéphane Graber-2
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On 01/31/2012 06:57 AM, Stéphane Graber wrote:
> I personally find this change risky for 12.04, I agree the
> hardcoded use of eth* and similar are hacks that we should get rid
> of, but I doubt we have the resources or time to check and fix the
> whole archive in time for 12.04.
>

If I'm reading Dell's email right, it seems like they've volunteered
to help fix the archive in this regard :)

Thanks,
Scott Ritchie

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Re: Using biosdevname by default?

Stéphane Graber-2
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On 02/05/2012 07:03 PM, Scott Ritchie wrote:

> On 01/31/2012 06:57 AM, Stéphane Graber wrote:
>> I personally find this change risky for 12.04, I agree the
>> hardcoded use of eth* and similar are hacks that we should get
>> rid of, but I doubt we have the resources or time to check and
>> fix the whole archive in time for 12.04.
>
>
> If I'm reading Dell's email right, it seems like they've
> volunteered to help fix the archive in this regard :)
>
> Thanks, Scott Ritchie

Which I really appreciate but realistically for Ubuntu 12.04, all
these fixes would need to be in the archive before Feature Freeze so
we can consider turning on biosdevname by default.

And don't get me wrong, I'm not saying that if these issues get fixed
in time for Feature Freeze, we'll automatically turn biosdevname on,
I'm just saying, that we could then have the discussion on whether we
want the feature or not for 12.04.

I tend to agree with Martin, that this would cause confusion and
likely break much more than our distro packages and scripts.

This really should have been discussed at UDS rather than showing up
so late in the development cycle.

To be safe, I'd much prefer having DELL and other interested users of
the feature help get these networking scripts fixed during the rest of
the cycle (as long as they are still considered bugfixes) and have a
session at UDS in Oakland on biosdevname and turning it on by default.

This should allow Dell and other interested manufacturers and users to
have something working in 12.04 by manually installing biosdevname on
their system and in their custom builds while not risking regressions
for the rest of our users.

- --
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com
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Re: Using biosdevname by default?

Robbie Williamson-2
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On 02/05/2012 06:16 PM, Stéphane Graber wrote:

> On 02/05/2012 07:03 PM, Scott Ritchie wrote:
>> On 01/31/2012 06:57 AM, Stéphane Graber wrote:
>>> I personally find this change risky for 12.04, I agree the
>>> hardcoded use of eth* and similar are hacks that we should get
>>> rid of, but I doubt we have the resources or time to check and
>>> fix the whole archive in time for 12.04.
>
>
>> If I'm reading Dell's email right, it seems like they've
>> volunteered to help fix the archive in this regard :)
>
>> Thanks, Scott Ritchie
>
> Which I really appreciate but realistically for Ubuntu 12.04, all
> these fixes would need to be in the archive before Feature Freeze
> so we can consider turning on biosdevname by default.

Am I wrong, or did Dell request that we enable this feature by default
for Dell Poweredge servers *only*, by detecting at boot...and that
they had done something similar with Fedora?  If we can contain this
change to only affecting Dell servers, then any issues it creates
would also only affect Dell servers...and I'd think Dell would have a
self-interest in helping us resolve those asap. Right?


- --
Robbie Williamson <[hidden email]>
robbiew[irc.freenode.net]

"Don't make me angry...you wouldn't like me when I'm angry."
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Re: Using biosdevname by default?

Mario Limonciello-2
On 02/05/2012 06:16 PM, Stéphane Graber wrote:
> To be safe, I'd much prefer having DELL and other interested users of
> the feature help get these networking scripts fixed during the rest of
> the cycle (as long as they are still considered bugfixes) and have a
> session at UDS in Oakland on biosdevname and turning it on by default.
The real advantage to this feature is on servers. I anticipate that most server users will stick with an LTS release instead.

On 02/05/2012 07:03 PM, Scott Ritchie wrote:
> If I'm reading Dell's email right, it seems like they've volunteered
> to help fix the archive in this regard 

John's team has had experience fixing this in Fedora.  Their work was of sufficient quality to be picked up by RHEL by default.
On 02/06/2012 09:44 AM, Robbie Williamson wrote:
Am I wrong, or did Dell request that we enable this feature by default
for Dell Poweredge servers *only*, by detecting at boot...and that
they had done something similar with Fedora?  If we can contain this
change to only affecting Dell servers, then any issues it creates
would also only affect Dell servers...and I'd think Dell would have a
self-interest in helping us resolve those asap. Right?
This is similar to what RHEL6 is doing.  They enable biosdevname by default only a limited subset of Dell machines ( http://rhn.redhat.com/errata/RHEA-2011-0644.html).

If this feature is picked up specifically for Dell machines, there will obviously be a vested interest to ensure the rest of the stack doesn't have problem related to hardcoded interface names. 

I'm unsure the timeline John's team will be able to commit to finding and fixing these things.  Feature freeze sounds a bit tight to me.  I've offered to help to review and sponsor his team's fixes however as they find them.


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Re: Using biosdevname by default?

James M. Leddy-2
On 02/06/2012 01:06 PM, Mario Limonciello wrote:

> I'm unsure the timeline John's team will be able to commit to finding
> and fixing these things.  Feature freeze sounds a bit tight to me.  I've
> offered to help to review and sponsor his team's fixes however as they
> find them.

I suspect that the hard part of this is installer changes, especially
since the scripts and applications that break as a result of using
biosdevname are probably not too distro-specific.


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Re: Using biosdevname by default?

Colin Watson
In reply to this post by Robbie Williamson-2
On Mon, Feb 06, 2012 at 09:44:51AM -0600, Robbie Williamson wrote:
> Am I wrong, or did Dell request that we enable this feature by default
> for Dell Poweredge servers *only*, by detecting at boot...and that
> they had done something similar with Fedora?

I thought I covered that in my original mail:

  "Firstly, I think it is in general unwise to make this kind of change
  for a single class of machine, at least for Ubuntu itself as opposed
  to vendor-specific builds.  The effect of doing that is to divide our
  testing efforts, so that tests of relevant functionality on one class
  of machine can no longer be presumed to be valid for others.  This
  usually ends up being to the detriment of everyone: Dell servers would
  no longer be able to take advantage of the testing we do on other
  classes of system."

Now, I can see that to some extent this is the server team's problem
rather than mine, so if you're saying that the server team is willing to
take this on and fix the associated foundational issues that our
networking expert has said it's likely to trigger, then I guess that's
fine.  I just find it a slightly disturbing precedent, and it would be
very easy to end up with a distribution whose behaviour was in practice
fragmented across systems.

Furthermore, it may be that Dell requested that Fedora enable this only
for PowerEdge servers, but that's not what they appear to have actually
implemented.
http://fedoraproject.org/wiki/Features/ConsistentNetworkDeviceNaming
(owned by a Dell engineer) says:

  "This feature affects all physical systems that expose network port
  naming information in SMBIOS 2.6 or later (specifically field types 9
  and 41).  Dell PowerEdge 10G and newer servers (PowerEdge 1950 III
  family, PowerEdge R710 family, and newer), and HP ProLiant G6 servers
  and newer are known to expose this information, as do some newer
  desktop models.  Furthermore, most older systems expose some
  information in the PCI IRQ Routing Table, which will be consulted if
  information is not provided by SMBIOS."

So, without being yet decided about biosdevname by default, I'm
wholeheartedly in agreement with Fedora that it should be all or nothing
if we don't want to risk lowering the quality of Ubuntu just on
PowerEdge servers, which I'm sure isn't the goal.

> If we can contain this change to only affecting Dell servers, then any
> issues it creates would also only affect Dell servers...and I'd think
> Dell would have a self-interest in helping us resolve those asap.

On the other hand, the people who will end up being responsible for
fixing the bugs may not have desperately convenient access to Dell
servers.  By making this behaviour system-specific, we make it harder
for our own developers to track down obscure corner cases.

Personally, my preferred approach would be something like this:

 1) Come up with a QA plan for 12.04 involving installing a cohort of
    test systems with biosdevname=1 and tracking down the associated
    problems.  That would permit Dell and others to use this in
    deployments, without risking the quality of the golden 12.04 images.
    (The above Fedora specification should help, since it links to a
    number of application-specific bug reports.)

 2) At UDS, consider defaulting to biosdevname=1 for 12.10.  Presumably
    by that point we would have reasonably substantial experience with
    it as a result of 1).

Cheers,

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Re: Using biosdevname by default?

Colin Watson
In reply to this post by Mario Limonciello-2
On Mon, Feb 06, 2012 at 12:06:50PM -0600, Mario Limonciello wrote:

> On 02/06/2012 09:44 AM, Robbie Williamson wrote:
> >Am I wrong, or did Dell request that we enable this feature by default
> >for Dell Poweredge servers *only*, by detecting at boot...and that
> >they had done something similar with Fedora?  If we can contain this
> >change to only affecting Dell servers, then any issues it creates
> >would also only affect Dell servers...and I'd think Dell would have a
> >self-interest in helping us resolve those asap. Right?
>
> This is similar to what RHEL6 is doing.  They enable biosdevname by
> default only a limited subset of Dell machines (
> http://rhn.redhat.com/errata/RHEA-2011-0644.html).

It's interesting that this appears to be at variance with what Fedora is
doing.  Of course, RHEL can take advantage of the separate broad testing
work done in Fedora, and then minimise the risk for their enterprise
distribution.  We don't have that luxury in Ubuntu.

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Re: Using biosdevname by default?

Colin Watson
In reply to this post by James M. Leddy-2
On Mon, Feb 06, 2012 at 04:48:32PM -0500, James M. Leddy wrote:
> On 02/06/2012 01:06 PM, Mario Limonciello wrote:
> > I'm unsure the timeline John's team will be able to commit to finding
> > and fixing these things.  Feature freeze sounds a bit tight to me.  I've
> > offered to help to review and sponsor his team's fixes however as they
> > find them.
>
> I suspect that the hard part of this is installer changes, especially
> since the scripts and applications that break as a result of using
> biosdevname are probably not too distro-specific.

No, the necessary installer changes are small and easily handled.  It's
the knock-on effects on the rest of the distribution that will take
time.

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Re: Using biosdevname by default?

Stéphane Graber-2
On 02/07/2012 06:08 AM, Colin Watson wrote:

> On Mon, Feb 06, 2012 at 04:48:32PM -0500, James M. Leddy wrote:
>> On 02/06/2012 01:06 PM, Mario Limonciello wrote:
>>> I'm unsure the timeline John's team will be able to commit to finding
>>> and fixing these things.  Feature freeze sounds a bit tight to me.  I've
>>> offered to help to review and sponsor his team's fixes however as they
>>> find them.
>>
>> I suspect that the hard part of this is installer changes, especially
>> since the scripts and applications that break as a result of using
>> biosdevname are probably not too distro-specific.
>
> No, the necessary installer changes are small and easily handled.  It's
> the knock-on effects on the rest of the distribution that will take
> time.

Correct, and the bits that'd break are very distro-specific, think
upstart jobs, udev rules and scripts included in packages like
ifenslave-2.6, bridge-utils, vlan, ifupdown.

All of these either come from Debian or are completely Ubuntu specific,
as far as I know, none of these directly come from upstream, so it's
unlikely that anything that was fixed for Fedora can be applied as-is to
Ubuntu.



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Re: Using biosdevname by default?

Matthew Garrett
In reply to this post by Colin Watson
On Tue, Feb 07, 2012 at 01:51:59AM +0000, Colin Watson wrote:
> On Mon, Feb 06, 2012 at 12:06:50PM -0600, Mario Limonciello wrote:
> > This is similar to what RHEL6 is doing.  They enable biosdevname by
> > default only a limited subset of Dell machines (
> > http://rhn.redhat.com/errata/RHEA-2011-0644.html).
>
> It's interesting that this appears to be at variance with what Fedora is
> doing.  Of course, RHEL can take advantage of the separate broad testing
> work done in Fedora, and then minimise the risk for their enterprise
> distribution.  We don't have that luxury in Ubuntu.

The change in RHEL was limited to a subset of machines since it was made
in a point release of an already shipped OS.

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Re: Using biosdevname by default?

Colin Watson
In reply to this post by Colin Watson
On Tue, Feb 07, 2012 at 01:50:19AM +0000, Colin Watson wrote:
>  2) At UDS, consider defaulting to biosdevname=1 for 12.10.  Presumably
>     by that point we would have reasonably substantial experience with
>     it as a result of 1).

biosdevname is now enabled by default on 12.10 alternate/server
installs.  This will cause some machines to use different (and more
stable across reboots) network interface names.

If you see network configuration failures during installation and you're
doing preseeded installations, check whether you've hardcoded the
previous network interface name in your preseed file.  If that's the
case, you can try one of the following:

 * Use "IPAPPEND 2" in your pxelinux.cfg, and remove any
   netcfg/choose_interface preseeding.  This will cause pxelinux to pass
   a BOOTIF= parameter to the installer corresponding to the interface
   used for PXE-booting, which d-i will use to select the same network
   interface for use during installation.

 * If you are not using pxelinux, or if you need to select a different
   interface for use during installation, you may preseed
   netcfg/choose_interface to a hardware MAC address in the form
   aa:bb:cc:dd:ee:ff to use an interface with that hardware address.

 * Find out the biosdevname-generated name for your network interface
   (remove the preseeding for netcfg/choose_interface and you should be
   shown a list of the available network interfaces; or use 'ip link
   show' after biosdevname has done its work) and use that instead.

 * As a last resort, pass the "biosdevname=0" boot parameter to return
   to the previous scheme for naming network interfaces.

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Re: Using biosdevname by default?

Steve Langasek-6
On Thu, Aug 23, 2012 at 04:23:53PM +0100, Colin Watson wrote:
> On Tue, Feb 07, 2012 at 01:50:19AM +0000, Colin Watson wrote:
> >  2) At UDS, consider defaulting to biosdevname=1 for 12.10.  Presumably
> >     by that point we would have reasonably substantial experience with
> >     it as a result of 1).

> biosdevname is now enabled by default on 12.10 alternate/server
> installs.  This will cause some machines to use different (and more
> stable across reboots) network interface names.

Thanks, Colin!

Are we expecting this to be enabled for the desktop image as well, for
consistency?

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Re: Using biosdevname by default?

Colin Watson
On Thu, Aug 23, 2012 at 11:17:03AM -0700, Steve Langasek wrote:

> On Thu, Aug 23, 2012 at 04:23:53PM +0100, Colin Watson wrote:
> > On Tue, Feb 07, 2012 at 01:50:19AM +0000, Colin Watson wrote:
> > >  2) At UDS, consider defaulting to biosdevname=1 for 12.10.  Presumably
> > >     by that point we would have reasonably substantial experience with
> > >     it as a result of 1).
>
> > biosdevname is now enabled by default on 12.10 alternate/server
> > installs.  This will cause some machines to use different (and more
> > stable across reboots) network interface names.
>
> Thanks, Colin!
>
> Are we expecting this to be enabled for the desktop image as well, for
> consistency?

I'm not sure about this, and would welcome thoughts.  On the one hand,
consistency is valuable.  On the other hand, I would expect the benefit
on typical desktop systems to be much less, and the change undeniably
has a cost; it's not clear to me that the trade-off makes sense on the
desktop.

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