Thanks, good ideas. I checked the UUIDs as you suggested and they are 
different. I then went ahead and hot-plugged another card I had with only a 
single partition. Lo and behold, this time it worked (mostly, see below).

I now also noticed on the board running Debian that the card with the two ext4 
partitions on it lacked a label for the second partition (it got auto-mounted 
under /media but using its UUID, not label). So I used e2label to give that 
partition a label, too. Then hot-plugged it into the board running the 
4.1.15-ti-r40 kernel under Ubuntu, which before would give the error with this 
card, and lo and behold it now worked (mostly, see below).

I wish I had re-tested the card just before doing this so it was clearer that 
all partitions having labels was really the only change. It’s a bit hard to 
believe that this would make the difference between the kernel succeeding or 
failing to initialize the card device. But other than a week of time having 
passed, I don’t know what else could have possibly changed. I also don’t have 
time right now to go back and recreate a card with 2 partitions one of which 
unlabeled (or is there a way to erase a label from a partition? tune2fs and 
e2label only talk about setting the label.).

By “worked mostly” I mean that the kernel properly recognizes the card and 
creates the block devices for both the card and the partitions on the card. 
Also, the symlinks under /dev/disk/by-id/ and /dev/disk/by-label are created 
(by udev rules, I believe?). What doesn’t happen on the Ubuntu/4.1.15-ti-r40 
board but does on the Debian/3.8.13-bone79 board is that the partitions get 
auto mounted under /media/<partitionLabel>. But I can now see and figure out 
what’s missing on the Ubuntu-running board, and at least right now for me that 
part isn’t so important.

  -hilmar

> On Feb 2, 2016, at 6:11 PM, Wally Bkg <[email protected]> wrote:
> 
> If you don't have another SD card to try and can lose these contents, its 
> worth trying a reformat to a single partition, although Ubuntu generally 
> seems very good at handling multi-partition SD cards.
> 
> I have hot plugged an SD card into Debian 7.9 (image 2015-11-12) same as you 
> have done, (the card I used to flash with) and it worked, although it didn't 
> automount.   I see in your first post you said your card worked on a Debian 
> 3.8 kernel, so  I'd suspect it may be a kernel version issue or something 
> wrong with the udev rules for your Ubuntu (sorry, I'm no help with these).
> 
> Just as I about to hit "POST" it occurred to me the flasher may have cloned 
> the image to the eMMC so the card may have the same UUID as the eMMC which 
> might mess up the udev rules.  Try blkid on your BBB to get the UUID of the 
> eMMC and do it with the SD card in another system to see if they are the same.
> 
> 
> On Monday, February 1, 2016 at 9:59:53 AM UTC-6, Hilmar Lapp wrote:
> Any chance someone has an idea what might be going wrong here? I’d be happy 
> to reformat the card or take other destructive measures, but right now the 
> device for the card is not even showing up under /dev when the card is 
> inserted.
> 
> Is it that the 4.1.15-ti-r40 kernel doesn’t support hot-plugging of uSD 
> cards? If so, anything I can do to change that? And I’m not sure how to boot 
> into the eMMC when the card is inserted in at boot. (The system will boot 
> into the SD card if inserted.)
> 
>   -hilmar
> 
>> On Jan 25, 2016, at 11:28 AM, Hilmar Lapp <[email protected] <javascript:>> 
>> wrote:
>> 
>> I am running the Ubuntu 14.04.3 image from Dec 11, 2015, on a Beaglebone 
>> Black, with updated packages and updated kernel. System details below. When 
>> I insert an SD card with 2 Linux partitions (and formatted ext4 filesystems) 
>> on it after boot, it fails to be recognized.  The following message appears 
>> in syslog:
>> 
>> Jan 25 11:01:52 hostname kernel: [47672.809891] mmc0: card never left busy 
>> state
>> Jan 25 11:01:52 hostname kernel: [47672.814264] mmc0: error -110 whilst 
>> initialising SD card
>> 
>> The odd thing is that first this is the same card onto which I wrote and 
>> then booted the downloaded image. I later flashed the card to the eMMC. So I 
>> can boot from the card successfully (which presumably means the kernel 
>> supports it), but when booting into the same kernel and rootfs from the 
>> eMMC, it's reported as failing to initialize. Also, I *can* insert the card 
>> perfectly fine into a BBB running Debian Wheezy with kernel 3.8.13-bone79 
>> booted from the eMMC - the kernel recognizes it, udisks-daemon fires, 
>> partitions get mounted etc, all without any errors. So I'm rather confident 
>> that the card is fine.
>> 
>> Anyone got any ideas what I might be missing?
>> 
>>   -hilmar
>> 
>> System details: starting image 
>> bone-ubuntu-14.04.3-console-armhf-2015-12-11-2gb.img
>> 
>> ubuntu@hostname:~$ lsb_release -a
>> No LSB modules are available.
>> Distributor ID:      Ubuntu
>> Description: Ubuntu 14.04.3 LTS
>> Release:     14.04
>> Codename:    trusty
>> ubuntu@hostname:~$ uname -a
>> Linux hostname 4.1.15-ti-r40 #1 SMP PREEMPT Fri Jan 8 09:45:11 UTC 2016 
>> armv7l armv7l armv7l GNU/Linux
>> 
>> 
>> 
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> -- 
> Hilmar Lapp -:- lappland.io <http://lappland.io/>
> 
> 
> 
> 
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