Plug in Micro SD with reader or plug in USB flash into Linux Box:

fdisk -l
...
Disk /dev/sde: 16.6 GB, 16574840832 bytes
...
/dev/sde1            2048    32372735    16185344   83  Linux
mkdir -p /mnt/sde1
mount /dev/sde1 /mnt/sde1
cd /mnt/sde1

from here we could restore the file of Yun OS.