Re: Question to new network device names
On Thursday 24 August 2017 12:30:37 Dan Ritter wrote:
> On Thu, Aug 24, 2017 at 10:43:56AM -0500, David Wright wrote:
> > On Thu 24 Aug 2017 at 10:20:52 (-0400), Dan Ritter wrote:
> > > There are, of course, five different ways to do this (at a
> > > minimum):
> > >
> > > 1. /dev/sda1 is based on discovery order. Changes in discovery
> > > order may indicate a significant problem that you need to
> > > investigate -- or not.
> >
> > I'm having difficulty imagining a scenario where the identity
> > of sdaX, in particular, is unimportant (for most people).
>
> Say you boot from /dev/nvme0n1p1 (a high speed NVMe SSD) and
> have /dev/sda, b, c and d in an mdadm RAID10.
>
> mdadm will scan all disks looking for its signature, and will
> assemble them into /dev/md/0 regardless of physical disk
> location. So it really won't matter to you whether you have the
> same disks in /dev/sdX from boot to boot as long as they are
> all there.
>
> But for most people, most of the time, swapping /dev/sda and
> /dev/sdc would be a problem.
>
> > But in connection with the original NIC discussion, the absence
> > of disk/by-uuid would be sorely missed if it weren't there, which
> > is why some improvement on eth0, eth1 assignment was needed,
> > and the result was a very flexible system IMO.
> >
> > > 6. Various advanced systems -- mdadm, LVM, btrfs, ZFS, hardware
> > > RAID -- have their own ideas about what to do and how to do it,
> > > which may include any of the above methods as well as their own
> > > peculiarities.
> > >
> > > That said, if you have a laptop or a desktop with 1-2 disks, you
> > > are probably going to be perfectly happy with either /dev/sda1 or
> > > LABEL=root-$HOSTNAME addressing.
> >
> > With two disks on a BIOS computer, you have an immediate problem,
> > don't you? That what disk-swapping was all about. And that was when
> > everything was on ATA.
>
> On a well-working computer, device discovery order is constant without
> physical changes. sda will always be sda, until it breaks or
> something else (bad) happens.
>
> > But now look at the debates here on, for example, how an SD card
> > is going to appear to the system. The schematic diagram of any
> > laptop looks like a forest of USBs (and other types) so which is
> > going to win the race to become sda?
>
> They don't. The SATA, SATA-DOM or NVMe disk selected by the UEFI or
> BIOS will become sda. Or if you've got an internal USB port with a
> stick in it, that might be a selected candidate. In no case
> should it change without hardware failure or physical
> rearrangement.
>
> The question is, how will your newly plugged in SD card become
> sdk rather than sdj, and the answer is that mass storage devices
> that are expected to be rearranged should be treated differently
> from those which are expected to always be available from
> boot-time onwards.
>
> > > Getting back to the original point, NIC names -- virtually every
> > > computer has exactly one or two NICs, and is best served by eth0
> > > and wlan0. The computers with 3-5 NICs are usually best served
> > > that way. More complex naming schemes are helpful when you have a
> > > router or switch, and it's nice that Debian supports that, but
> > > hardly a good default.
> >
> > There are plenty of ways that you, or Debian, can set a default.
> > But it surprises me that so many people grumble about this change.
>
> People grumble about changes for several nonexclusive reasons:
>
> 1. The change broke what they were doing.
> 2. The change broke their mental model of what they were doing.
> 3. The change did not bring them perceived benefits.
> 4. The change appears arbitrary.
> 5. The change fixed a problem but they perceive better ways to
> solve the problem.
> 6. The change creates new problems.
>
> > The history of computing is littered with statements like
> > "virtually every computer has exactly one or two NICs".
>
> It used to be zero.
>
> We are currently in the phase of history where this statement is
> true. NICs are both ubiquitous and cheap, yet devices tend to
> come with one (only an ethernet port or only a wifi radio) or
> two (one of each of those, or a wifi radio and a cell radio).
>
> Devices can add more, but they are always special cases: my
> Debian-running firewall has 5 ethernet ports. I occasionally
> add a USB ethernet frob in order to isolate a device that I want
> to talk to directly. Special cases deserve special treatment.
>
> I expect the statement to remain true for the next ten years.
>
> Do you expect differently? If so, why?
>
> > This list is full of postings about the complex DNS system. But
> > how long did /etc/hosts last? Some complexity is unavoidable,
> > but if you try to avoid it, you pay for it later. Look at timezones.
> > Ever allowing computers' internal clocks to run on local time
> > was, with hindsight, a big mistake. Leap seconds might also
> > be seen the same way (still under debate).
>
> /etc/hosts still acts the way it always did -- put in an entry,
> it overrides DNS.
>
That depends entirely on who wrote your /etc/resolv.conf and whether or
not your did a sudo chattr +i /etc/resolv.conf, immediately after
verifying that it works. (and of course that implies it is a real file,
not a softlink to something else. With N-M in the mix and active that
is the only way to keep it from tearing down your network configuration
and leaving you empty files, and no network, if it cannot find a dhcpd
server)
> Timezones are a human legal-social problem, and the ability of
> technology to deal with those is known to be problematic.
Just as humans are known to be a problem...
> -dsr-
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>
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