apt install overlayroot
update-initramfs -uk `uname -r`

# Then in /boot/uEnv.txt:
cmdline=coherent_pool=1M net.ifnames=0 lpj=1990656 rng_core.default_quality=100 quiet overlayroot=tmpfs

root@BeagleBone:~# cat /etc/fstab
# /etc/fstab: static file system information.
#
# Auto generated by RootStock-NG: setup_sdcard.sh
#
/dev/mmcblk0p1  /  ext4  noatime,errors=remount-ro  0  0
debugfs  /sys/kernel/debug  debugfs  mode=755,uid=root,gid=gpio,defaults  0  0