replace_rpi2_sdcard_copy_rootfs

wget http://cdimage.ubuntu.com/ubuntu/releases/16.04/release/ubuntu-16.04.5-preinstalled-server-armhf+raspi2.img.xz

# tarpipe backup rootfs (tar rootfs, one-filesystem to stdout)
tar -cpf - --one-file-system / | ssh user@remote "( cat > /path/to/backup/rootfs.tar )" 

# install rpi2 ubuntu image to sdcard (I used usb sdcard reader)
xzcat ubuntu-16.04.5* | dd of=/dev/sda bs=4M
sync;sync;sync
blockdev --rereadpt /dev/sda

# grow rootfs partition
growpart /dev/sda 2

# grow ext4 filesystem
e2fsck /dev/sda2
resize2fs /dev/sda2

# mount and unpack backup tar
mount /dev/sda2 /mnt
tar -C /mnt -xvpf /path/to/backup/rootfs.tar --numeric-owner