Disable Beaglebone Black flashing heartbeat LED

persistently (permanently) disable BBB flashing heartbeat LED:

sudo nano /etc/rc.local

and paste in:

echo none > /sys/class/leds/beaglebone\:green\:usr0/trigger
echo none > /sys/class/leds/beaglebone\:green\:usr1/trigger
echo none > /sys/class/leds/beaglebone\:green\:usr2/trigger
echo none > /sys/class/leds/beaglebone\:green\:usr3/trigger

Reference

temporary disable heartbeat LED (only until rebooting)

sudo -s
echo none > /sys/class/leds/beaglebone:green:usr0/trigger
exit