$ cat /boot/uboot/snappy-system.txt 
# This is a snappy variables and boot logic file and is entirely generated and
# managed by Snappy. Modifications may break boot
######
# functions to load kernel, initrd and fdt from various env values
loadfiles=run loadkernel; run loadinitrd; run loadfdt
loadkernel=load mmc ${mmcdev}:${mmcpart} ${loadaddr} ${snappy_ab}/${kernel_file}
loadinitrd=load mmc ${mmcdev}:${mmcpart} ${initrd_addr} ${snappy_ab}/${initrd_file}; setenv initrd_size ${filesize}
loadfdt=load mmc ${mmcdev}:${mmcpart} ${fdtaddr} ${snappy_ab}/dtbs/${fdtfile}

# standard kernel and initrd file names; NB: fdtfile is set early from bootcmd
kernel_file=vmlinuz
initrd_file=initrd.img
fdtfile=am335x-boneblack.dtb

# extra kernel cmdline args, set via mmcroot
snappy_cmdline=init=/lib/systemd/systemd ro panic=-1 fixrtc

# boot logic
# either "a" or "b"; target partition we want to boot
snappy_ab=b
# stamp file indicating a new version is being tried; removed by s-i after boot
snappy_stamp=snappy-stamp.txt
# either "regular" (normal boot) or "try" when trying a new version
snappy_mode=regular
# if we're trying a new version, check if stamp file is already there to revert
# to other version
snappy_boot=if test "${snappy_mode}" = "try"; then if test -e mmc ${bootpart} ${snappy_stamp}; then if test "${snappy_ab}" = "a"; then setenv snappy_ab "b"; else setenv snappy_ab "a"; fi; else fatwrite mmc ${mmcdev}:${mmcpart} 0x0 ${snappy_stamp} 0; fi; fi; run loadfiles; setenv mmcroot /dev/disk/by-label/system-${snappy_ab} ${snappy_cmdline}; run mmcargs; bootz ${loadaddr} ${initrd_addr}:${initrd_size} ${fdtaddr}


$ snappy list
Name                Date       Version Developer 
ubuntu-core         2015-06-05 79      ubuntu    
hello-dbus-app      2015-06-01 1.0.1   canonical 
hello-dbus-fwk      2015-06-01 1.0.0             
hello-world         2015-06-08 1.0.17  canonical 
beagleblack         2015-06-01 1.7.1       


$ cat /etc/system-image/channel.ini 
[service]
base: system-image.ubuntu.com
http_port: 80
https_port: 443
channel: ubuntu-core/15.04/edge
device: generic_armhf
build_number: 79
version_detail: ubuntu=20150605.3,raw-device=20150605.3,version=79


$ cat /writable/cache/system/etc/system-image/channel.ini 
[service]
base: system-image.ubuntu.com
http_port: 80
https_port: 443
channel: ubuntu-core/15.04/edge
device: generic_armhf
build_number: 82
version_detail: ubuntu=20150609,raw-device=20150609,version=82