Because of a typo in the chmod command, the / usr / bin directory was blocked on Ubuntu 16.04.
Result of the ls -l :
d --------- 2 root root 69632 Oct 8 15:51 bin
When trying to use chmod error:
bash: / usr / lib / command-not-found: / usr / bin / python3: bad interpreter: Access denied
Is it possible to restore rights?