Quick heads up - in case someone else gets this same error
It appears that apt-get upgrade needs a reasonable amount of memory to work with. It depends what you Raspberry Pi is doing (mine is running as a squid proxy server), but you may need to free up some memory when running the upgrade. You only need to follow this if you get the "Failed to fork" error during the upgrade.
The error I got during the upgrade was:
315 upgraded, 0 newly installed, 0 to remove and 11 not upgraded.
FATAL -> Failed to fork.
whilst this may sound like it's done the upgrade before the failure it hasn't in fact started downloading / installing packages.
Failed to fork may sound like a problem with trying to pick up peas at dinner time - but in simple terms it means it couldn't start the new process to perform the update - most likely a memory problem.
Quick check shows that I had 10MB free memory, although significant amount of swap in use.
Code: Select all
free
total used free shared buffers cached
Mem: 188104 177744 10360 0 5288 13632
-/+ buffers/cache: 158824 29280
Swap: 102396 102204 192
In my case a quick reboot helped clear the memory. If you don't want to completely reboot you could look at stopping some services or shutting down certain applications to see if that helps.
After reboot I had more available memory and swap usage was back to 0.
Code: Select all
free
total used free shared buffers cached
Mem: 188104 162808 25296 0 13532 73380
-/+ buffers/cache: 75896 112208
Swap: 102396 0 102396
and repeating the sudo apt-get upgrade is now progressing nicely.
Good that the plan for the Model A has the same memory as the Model B, otherwise I could see problems like this happening a bit more in future.