Trying to get WiFi working on the Raspberry Pi 3 following the instructions found at https://www.raspberrypi.org/documentation/configuration/wireless/wireless-cli.md when I got to start the WiFi using
sudo wpa_cli reconfigure
sudo wpa_cli reconfigure
sudo wpa_cli reconfigure
It reports an error:
Failed to connect to non-global ctrl_ifname: (null) error: No such file or directory
Error messages like this are great as they don’t provide any clue’s, anyway the fix for me was simple once found. Run:
sudo ifdown wlan0
sudo ifdown wlan0
sudo ifdown wlan0
This may error with a message
ifdown: interface wlan0 not configured
ifdown: interface wlan0 not configured
ifdown: interface wlan0 not configured
Don’t give up! Still run
sudo ifup wlan0
sudo ifup wlan0
sudo ifup wlan0
That fixed it for me. Hope it helps you too! 
I’m using Raspbian GNU/Linux 8 (jessie). uname -a returns
Linux <hostname> 4.4.50-v7+ #970 SMP Mon Feb 20 19:18:29 GMT 2017 armv7l GNU/Linux
Linux <hostname> 4.4.50-v7+ #970 SMP Mon Feb 20 19:18:29 GMT 2017 armv7l GNU/Linux
Linux <hostname> 4.4.50-v7+ #970 SMP Mon Feb 20 19:18:29 GMT 2017 armv7l GNU/Linux
