（1）首先查看空间：
firefly@firefly:~$ df -h
Filesystem Size Used Avail Use% Mounted on
udev 1.9G 8.0K 1.9G 1% /dev
tmpfs 391M 1.3M 389M 1% /run
/dev/mmcblk0p6 6.6G 6.6G 0 100% /root-ro
/dev/mmcblk0p7 22G 739M 22G 4% /userdata
overlayroot 22G 739M 22G 4% /
tmpfs 2.0G 0 2.0G 0% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 2.0G 0 2.0G 0% /sys/fs/cgroup
tmpfs 391M 0 391M 0% /run/user/0
tmpfs 391M 16K 391M 1% /run/user/1000
（3）运行ff_export_rootfs：
firefly@firefly:~$ sudo ff_export_rootfs /home/firefly/
MEDIA FREE SPACE SIZE 21564 MBytes
EXPORT IMAGE SIZE 8352 MBytes
BLOCK_COUNT 11380420
INODE_COUNT 363292
sync…
rsync: write failed on "/home/firefly/tmp.icvz6qxK9v/home/firefly/Ubuntu18.04.6LTS_Firefly_exspace left on device (28)
rsync error: error in file IO (code 11) at receiver.c(393) [receiver=3.1.2]
（3）我的空间为22G,rootfs也才10G，不知道为什么不够：
firefly@firefly:~$ df -h /home/firefly/
Filesystem Size Used Avail Use% Mounted on
overlayroot 22G 739M 22G 4% /