How to use overlayfs on Linux
Contents
1 What Is OverlayFS
OverlayFS is a union mount filesystem implementation for Linux. It allows a virtual merge of two partitions, while keeping their actual contents separate. One partition is the rootfs partition and the other is the data partition. It has the following advantages:
1) you can easily restore a system's factory settings by formatting the data partition;
2) you can still boot your system since the rootfs is read-only even when the data partition cannot be correctly mounted due to unexpected shutdown.
2 FriendlyELEC's Systems That Support OverlayFS
2.1 Hardware Systems
H3, H5, S5P4418, S5P6818, RK3399 based boards
2.2 OS Systems
FriendlyCore, FriendlyDesktop, Lubuntu
3 How to Check Whether OverlayFS Is Working
Run the df command. If the "/" partition is mounted as "overlay" it means OverlayFS is working;
pi@NanoPi-M1-Plus:~$ df Filesystem 1K-blocks Used Available Use% Mounted on udev 474848 0 474848 0% /dev tmpfs 102304 3564 98740 4% /run overlay 28925547 1315493 26112465 5% / tmpfs 511512 0 511512 0% /dev/shm tmpfs 5120 4 5116 1% /run/lock tmpfs 511512 0 511512 0% /sys/fs/cgroup /dev/mmcblk0p1 40862 11852 29010 30% /boot tmpfs 102304 0 102304 0% /run/user/1000
4 Partition Settings With OverlayFS
If OverlayFS is enabled in your system there will be three partitions:rootfs, data and boot, and these partitions correspond to a rootfs.img, a userdata.img and a boot.img separately:
root@NanoPi-M1-Plus:~# lsblk /dev/mmcblk0 NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT mmcblk0 179:0 0 29.7G 0 disk |-mmcblk0p2 179:2 0 1.2G 0 part |-mmcblk0p3 179:3 0 28.5G 0 part `-mmcblk0p1 179:1 0 40M 0 part /boot
The system data will be in the rootfs partition and the data written to the root directory will be in the data partition.
5 Restore Factory Settings With OverlayFS
5.1 Method 1: Operate in Userdata Partition
factory reset:
mount /dev/mmcblk0p3 /media/ && cd /media/ mv root/ deleteme.root mv work/ deleteme.work reboot
cleanup after reboot:
mount /dev/mmcblk0p3 /media/ && rm -rf /media/deleteme.*
5.2 Method 2: Restore by Setting Commandline Parameters
5.3 S5P4418 & S5P6818 platform
Add "wipedata=yes" to the kernel's commandline parameters. For S5P4418 and S5P6818 based boards you can do it after system boots;
5.3.1 恢复出厂设置
sudo fw_setenv bootargs "`sed 's/ wipedata=yes//g;s/ wipedata=no//g' /proc/cmdline` wipedata=yes" sudo reboot
5.3.2 Keep Data in Data Partition on System Reboot
sudo fw_setenv bootargs "`sed 's/ wipedata=yes//g;s/ wipedata=no//g' /proc/cmdline` wipedata=no" sudo reboot
For other SoC based boards you need to make changes in the kernel commandline by following the methods supported by their BSPs or by entering uboot to proceed.
5.3.3 RK3399 platform
echo wipedata=yes > /var/.init_wipedata; sync; reboot
The next time you boot to the ramdisk stage, the data partition will be formatted, and the /var/.init_wipedata file will also be deleted.
5.3.4 H3/H5 platform
5.3.4.1 change boot.cmd
Enter the boot directory and modify file boot.cmd, change the following:
setenv bootargs "console=${debug_port} earlyprintk
root=/dev/mmcblk0p2 rootfstype=ext4 rw rootwait fsck.repair=${fsck.repair}
panic=10 fbcon=${fbcon} ${hdmi_res} ${overlayfs} ${pmdown}"to:
setenv bootargs "console=${debug_port} earlyprintk
root=/dev/mmcblk0p2 rootfstype=ext4 rw rootwait fsck.repair=${fsck.repair}
panic=10 fbcon=${fbcon} ${hdmi_res} ${overlayfs} ${pmdown} wipedata=yes"Added wipedata=yes.
5.3.4.2 regenerate boot.scr
Enter the boot directory，execute the following command：
$ mkimage -C none -A arm -T script -d boot.cmd boot.scr
6 Disable OverlayFS
If you have an installation TF card, use the fdisk command to delete the data partition.
