After upgrading to Ubuntu 20.04, Ruby on Rails gem installations fail. If you use rvm this fails with rvm-managed environments too. Running
You will see errors that look like this (in this case it's the byebug gem but other gems will also give the same error):
ERROR: Error installing byebug:
ERROR: Failed to build gem native extension.
make DESTDIR\= install
make: /usr/bin/mkdir: Command not found
The problem is that Ubuntu 20.04 changes the location of the mkdir command, moving it from /usr/bin to /bin.
The easiest solution is to symbolically link the mkdir command back into /usr/bin.
- su - to root (or use sudo to execute the command below)
- ln -s /bin/mkdir /usr/bin/