This topic has been addressed a few times - a lot of help, but no definitive answer. Here’s how I did it.
I gleaned a lot of good info in the post by @gasketse in the discussion with @TonyPh12345 here “Not enough space for upgrade error” . My heartfelt thanks guys! In fact, the symptoms I experienced, and the tack I took to attempt to resolve the problem were exactly those taken by @gasketse (including the long backup and the “System Only” factory restore). So, I’ll not reproduce the symptoms here.
@TonyPh12345 was 100% correct when he deduced that “The fact that it’s not finding DataVolume means the AWK command is returning “nul,” which gets interpreted as NO space.”
I executed “df -a”, in case the vanilla df itself was not working as expected, and voila - the output included /DataVolume.
I then (after making copies) modified the shell scripts /usr/local/sbin/updateFirmwareFromFile.sh and /usr/local/sbin/updateFirmwareToLatest.sh by adding the -a switch as follows:
df | grep /DataVolume”
was changed to
df -a | grep /DataVolume”
this modification fed the subsequent awk with the correct input allowing the script to continue.
The reason I changed both files, was that I was still undecided which method I was going to use to do the update.
As it turns out, it was too late for me to continue, so I decided to leave it till next day to continue. Lo and behold, at 05:39 the next morning the My Cloud decided to autoupdate anyway. The autoupdate feature had never worked for me and I was about two years behind in upgrades - due to the disk space problem.
All seems good now - but slow because system is re-scanning…
Oh, yes, and my df command now, after the update, works the way TonyPH’s did - no more need for the -a. I also suspect that my original problem occurred because of an apt-get - I’m sure WD could control that better. Anyhow, lesson learned and I’m back to standard. I ran the apt-get because of issues I was having with failing TimeMachine backups. Now I back up to a MyPassport - crude, I know…