I tried to install a custom firmware (w/ built-in Node v6) from this: http://www.joemotacek.com/putting-a-newer-version-of-node-js-on-linkit-smart-7688-duo/
And the problem is I can't mount root fs to SD Card anymore (from this instruction: https://docs.labs.mediatek.com/resource/linkit-smart-7688/en/tutorials/file-storage/mounting-the-root-fs-on-an-sd-card)
It used to work in the official firmware (0.9.4).
The error starts as some packages can't be downloaded from opkg update. And when I tried to type
mount /dev/mmcblk0p1 /mnt
mounting mmcblk0p1 failed with Invalid argument
And now It's getting worse, I can't even access /Media/SD anymore. With this error
can't open '/Media/SD-P1': Too many levels of symbolic links