$ sudo ubuntu-device-flash --verbose core --output=snappy.img --developer-mode --channel=stable 15.04
Determining oem configuration
Starting download of generic-amd64
40.93 KB / 40.93 KB [========================================================================================================] 100.00 % 99.47 KB/s 
Done
operation not supported
2015-06-09 08:55:24 ERROR snappy logger.go:199 generic-amd64 failed to install: unpack /tmp/generic-amd64310762128 to /tmp/oem535521461/oem/generic-amd64/1.1.1 failed with exit status 1
generic-amd64 failed to install: unpack /tmp/generic-amd64310762128 to /tmp/oem535521461/oem/generic-amd64/1.1.1 failed with exit status 1