Script for restarting wpa_supplicant in debug mode

wpa_debug.sh

#!/bin/sh

# set wpa_supplicant debug level to 1, disable timestamps, disable show_keys

[ "$UID" == 0 ] || { echo "Only root can run this"; exit 0;}

LOG="/var/log/wpa_supplicant.log"

echo "Stopping NetworkManager"
service network-manager stop
sleep 1 

echo "Killing current wpa_supplicant"
pkill -9  wpa_supplicant$
sleep 1 

echo "Starting wpa_supplicant in DBUS & DEBUG mode, log is in $LOG"
wpa_supplicant -dd -u -f $LOG -B
sleep 1

echo "Starting NetworkManager"
service network-manager start

What if just run sudo wpa_cli log_level debug ?

May be too late. In the latest wpa_supplicant, you have to enable logging by building it with DEBUG_LOG_FILE=y in the .config file to enable the -f flag.