Maybe you already did this....
For the mrfixit distro, if you login as rock, there is an update icon, lower right, near time
Any other login does not have this
This update (mrfixit_update.sh,, in /usr/bin,, IIRR) update kernel and uboot, actually installs uboot (uniquely)
Later uboots have some capability to usb boot, doesn't always work, try both sockets
Do be aware that a LOT, majority of uSD are crap, at least as a hd for OS, OK for cameras etc
For the mrfixit distro, if you login as rock, there is an update icon, lower right, near time
Any other login does not have this
This update (mrfixit_update.sh,, in /usr/bin,, IIRR) update kernel and uboot, actually installs uboot (uniquely)
Later uboots have some capability to usb boot, doesn't always work, try both sockets
Do be aware that a LOT, majority of uSD are crap, at least as a hd for OS, OK for cameras etc