Udev Question

[Lonni J Friedman]

I'm not sure of the why, but this is how udev works.  It keeps a
record of every piece of HW.  I've seen this very same behavior when
swapping hard disks between systems, and I usually need to either hack
udev's database to reset back to eth0, or just reconfigure the network
settings to work from the new ethernet numbering assignments.

On Sat, Jun 19, 2010 at 12:53 PM, C M Reinehr <cmr at amsent.com> wrote:
> Thursday what should have been a relatively simple problem became much more
> interesting owing the udev system.
>
> I have two identical servers -- identical hardware & running exactly the same
> version of Debian Linux (Lenny) with almost identical software (same system
> software but different applications).
>
> Both use a Tyan Thunder motherboard which came with three ethernet ports: two
> Broadcom gigabit Ethernet ports plus one Intel 10/100 Ethernet port. For five
> years, when booting, the system (udev?) would discover first one of the
> Broadcom ports and name it eth0, then the Intel port as eth1 & finally the
> remaining Broadcom port as eth2. My /etc/network/interfaces file was
> configured accordingly to assign static IP numbers and set up routes (copy
> below) per their MAC numbers.
>
> Thursday, while performing some minor software maintenance I rebooted one of
> the servers -- running my accounting software -- or, at least, attempted to
> reboot one of the servers. It wouldn't boot. The lights & fans powered up but
> no POST screen. This was a critical server: no accounting software, no sales
> order entry, no sales, no money, etc.
>
> After fooling with that for a while and deciding that the system was down for
> the count (probably with a failing power supply) I decided the simplest &
> fasted way of recovering was to remove the hard drives from the dead server &
> swap them for the hard drives of the running server (SCSI RAID enclosures
> with hot-swapable drives). I didn't hot swap them, but powered everything
> down, swapped the drives & restarted the good server.
>
> All was right with the world until I discovered that I had no network
> connectivity -- which meant I was back to being screwed, again. After about
> two hours of fumbling in the dark I finally figured out what was happening.
> Udev was now assigning my network ports as eth3, eth4 & eth5, instead of 0,
> 1, & 2. Since this didn't match was was configured in interfaces, the ports
> were not being initialized. After editing the interfaces file accordingly, I
> had network access again and this behavior repeated itself through several
> subsequent reboots.
>
> Finally, my question is why was udev reassigning the port names? Here's a
> snippet of the dmesg file:
>
> [   40.526949] ACPI: PCI Interrupt 0000:03:08.0[A] -> GSI 18 (level, low) ->
> IRQ 18
> [   40.630945] e100: eth0: e100_probe: addr 0xfeafb000, irq 18, MAC addr
> 00:e0:81:29:ae:1b
> [   40.630945] tg3.c:v3.92.1 (June 9, 2008)
> [   40.630945] ACPI: PCI Interrupt 0000:02:09.0[A] -> GSI 24 (level, low) ->
> IRQ 24
> [   40.647089] udev: renamed network interface eth0 to eth3
> [   40.651233] eth0: Tigon3 [partno(BCM95704A7) rev 2003 PHY(5704)]
> (PCIX:100MHz:64-bit) 10/100/1000Base-T Ethernet 00:e0:81:29:ae:5e
> [   40.651410] eth0: RXcsums[1] LinkChgREG[0] MIirq[0] ASF[0] WireSpeed[1]
> TSOcap[1]
> [   40.651562] eth0: dma_rwctrl[769f4000] dma_mask[64-bit]
> [   40.654946] ACPI: PCI Interrupt 0000:02:09.1[B] -> GSI 25 (level, low) ->
> IRQ 25
> [   40.671169] usb 1-2: new full speed USB device using ohci_hcd and address 2
> [   40.677140] eth1: Tigon3 [partno(BCM95704A7) rev 2003 PHY(5704)]
> (PCIX:100MHz:64-bit) 10/100/1000Base-T Ethernet 00:e0:81:29:ae:5f
> [   40.677318] eth1: RXcsums[1] LinkChgREG[0] MIirq[0] ASF[0] WireSpeed[1]
> TSOcap[1]
> [   40.677470] eth1: dma_rwctrl[769f4000] dma_mask[64-bit]
> [   40.680862] udev: renamed network interface eth0 to eth4
> [   40.708863] udev: renamed network interface eth1 to eth5
>
> If I'm reading this correctly, each port was initially assigned the usual
> eth0, 1 or 2, but then almost immediately renamed eth3, 4 or 5.
>
> Here is my interfaces file:
>
> # This file describes the network interfaces available on your system
> # and how to activate them. For more information, see interfaces(5).
>
> # The loopback network interface
> auto lo
> iface lo inet loopback
>
> # The first 100/1000 kbps ethernet nic
> auto eth4
> iface eth4 inet static
>        address 192.168.168.11
>        netmask 255.255.255.0
>        hwaddress ether 00:E0:81:29:AE:5F
>        gateway 192.168.168.168
>
> # The 10/100 kbps ethernet nic
> auto eth3
> iface eth3 inet static
>        address 192.168.168.10
>        netmask 255.255.255.0
>        hwaddress ether 00:E0:81:29:AE:1B
>        pointopoint 192.168.168.13
>        up route add -host 192.168.168.13 dev $IFACE
>        down route del -host 192.168.168.13 dev $IFACE
>
> # The second 100/1000 kbps ethernet nic
> auto eth5
> iface eth5 inet static
>        address 192.168.168.12
>        netmask 255.255.255.0
>        hwaddress ether 00:E0:81:29:AE:5E
>        pointopoint 192.168.168.9
>        up route add -host 192.168.168.9 dev $IFACE
>        down route del -host 192.168.168.9 dev $IFACE
>
> I almost left out, that since the MAC addresses were different I had to edit
> the interfaces file to correct for that, but that didn't cause or correct the
> udev renaming.
>
> If you've read this far, then very sincerely, thanks for your patience and any
> insights you may have. I'm up and running, but I really would like to
> understand what is happening here.



-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
L. Friedman                                    netllama at gmail.com
LlamaLand                       https://netllama.linux-sxs.org