What does errno=13 mean when connecting via OpenVPN?

Question

The tail-end of an OpenVPN connection (that otherwise appears successful) says (with leading timestamps omitted):

Note: Cannot open TUN/TAP dev /dev/net/tun: Permission denied (errno=13)
Note: Attempting fallback to kernel 2.2 TUN/TAP interface
Cannot allocate TUN/TAP dev dynamically
Exiting

What is the problem here?

Answer 1

Preface you OpenVPN command (line) with sudo...

i.e. the command requires root access to operate successfully