Snappy update fails because of its looking for non existing /writable/cache/assets/vmlinuz

It did not help that i renamed my kernel to vmlinuz - still the same error.

There is also some other initrd in that folder (not from my device tree)
ls /writable/cache/assets
initrd.img initrd.img-3.19.0.0-23-generic

Manuall faking update by setting the uboot.env variables boots just fine into the updated system.

(ODROIDC)root@odroid:~# snappy list -v
Name Date Version Developer
ubuntu-core 2015-07-23 129 ubuntu*
ubuntu-core 2015-07-23 129 ubuntu
odroidc 2015-07-23 0.3 *
(ODROIDC)root@odroid:~# snappy update
Installing ubuntu-core (130)
Starting download of ubuntu-core
Applying update[\]
Apply done
Updating boot files
25.77 MB / 25.77 MB [====================================] 100.00 % 932.14 KB/s
Done
can not find file /writable/cache/assets/vmlinuz
(ODROIDC)root@odroid:~# snappy list -v
Name Date Version Developer
ubuntu-core 2015-07-23 129 ubuntu*
ubuntu-core 2015-07-23 130 ubuntu!
odroidc 2015-07-23 0.3 *
Reboot to use the new ubuntu-core.
(ODROIDC)root@odroid:~# fw_setenv snappy_ab b
(ODROIDC)root@odroid:~# fw_setenv snappy_mode try
(ODROIDC)root@odroid:~# reboot

(ODROIDC)root@odroid:~# snappy list -v
Name Date Version Developer
ubuntu-core 2015-07-23 130 ubuntu*
ubuntu-core 2015-07-23 129 ubuntu
odroidc 2015-07-23 0.3 *

(ODROIDC)root@odroid:~# fw_printenv snappy_mode
snappy_mode=regular
(ODROIDC)root@odroid:~# fw_printenv snappy_ab
snappy_ab=b

I investigated this issue this morning. I can reproduce it by booting into 15.04/alpha on the BBB version r131. Then I set it back to r130 and got the same error message as you did. It appears the delta that got generated is faulty:

The delta from 130 to 131 is:
"""
        {
            "base": 130,
            "description": "ubuntu=20150723.5,raw-device=20150723.5,version=131",
            "files": [
...
                {
                    "checksum": "fbc5f3e27b4f8ad4325b6eca1f2a901adbaf5ffd15d5e813af596e45a06b1269",
                    "order": 1,
                    "path": "/pool/device-e800ea84eba34de0a6d7d05503e8324c40e4fbd56942d331b4acfb5bf1cd3ae0.delta-device-b318f1faee86d202efa9577e757b2769ed0f958a1a44378621ed14528850d1c8.tar.xz",
                    "signature": "/pool/device-e800ea84eba34de0a6d7d05503e8324c40e4fbd56942d331b4acfb5bf1cd3ae0.delta-device-b318f1faee86d202efa9577e757b2769ed0f958a1a44378621ed14528850d1c8.tar.xz.asc",
                    "size": 13594800
                },
...
            ],
            "type": "delta",
            "version": 131,
            "version_detail": "ubuntu=20150723.5,raw-device=20150723.5,version=131"
"""

When I download /pool/device-e800ea84eba34de0a6d7d05503e8324c40e4fbd56942d331b4acfb5bf1cd3ae0.delta-device-b318f1faee86d202efa9577e757b2769ed0f958a1a44378621ed14528850d1c8.tar.xz I see the following in the hardware.yaml:

kernel: assets/vmlinuz
initrd: assets/initrd.img
partition-layout: system-AB
hashes: 73d20f826ae7ec09671950057dee0db8-130377ee7d73559ee88a7279df5716d4
dtbs: assets/dtbs
bootloader: u-boot

but the assets directory does not contain a kernel - only the initrd.img. So this looks like a issue with either the delta generation or with our livecd-rootfs that generates the initrd.

I can reproduce it when updating in bbb from r146 to r147:

sudo ubuntu-device-flash core 15.04 -o bbb-1504-1-edge.img --revision=146 --channel edge --oem beagleblack --developer-mode

# dd and ssh

(BeagleBoneBlack)ubuntu@localhost:~$ sudo snappy list -v
Name Date Version Developer
ubuntu-core 2015-09-14 146 ubuntu*
ubuntu-core 2015-09-14 146 ubuntu
beagleblack 2015-09-15 1.12 canonical*
(BeagleBoneBlack)ubuntu@localhost:~$ sudo snappy update
Installing ubuntu-core (147)
Starting download of ubuntu-core
Applying update[/]
Apply done
Updating boot files
15.13 MB / 15.13 MB [=============================================================================================================================] 100.00 % 223.47 KB/s
Done
can not find file /writable/cache/assets/vmlinuz
(BeagleBoneBlack)ubuntu@localhost:~$ snappy list -v
Name Date Version Developer
ubuntu-core 2015-09-14 146 ubuntu*
ubuntu-core 2015-09-15 147 ubuntu!
beagleblack 2015-09-15 1.12 canonical*
Reboot to use the new ubuntu-core.
(BeagleBoneBlack)ubuntu@localhost:~$ ls /writable/cache/assets/
initrd.img initrd.img-3.19.0-28-generic

Reboot seems to work fine and let the system in the b partition with the system updated:

(BeagleBoneBlack)ubuntu@localhost:~$ snappy list -v
Name Date Version Developer
ubuntu-core 2015-09-15 147 ubuntu*
ubuntu-core 2015-09-14 146 ubuntu
beagleblack 2015-09-15 1.12 canonical*

Rollback and update work too from there.