View source for How to use overlayfs on S5P4418/S5P6818/H3/H5 platform

[[How to use overlayfs on Linux/zh|查看中文]]

==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:<br />
1) you can easily restore a system's factory settings by formatting the data partition;<br />
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.<br />

==FriendlyELEC's Systems That Support OverlayFS==
===Hardware Systems===
H3, H5, S5P4418, S5P6818, RK3399 based boards
===OS Systems===
FriendlyCore, FriendlyDesktop, Lubuntu

==How to Check Whether OverlayFS Is Working==
Run the df command. If the "/" partition is mounted as "overlay" it means OverlayFS is working;
<syntaxhighlight lang="bash">
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
</syntaxhighlight>

==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:
<syntaxhighlight lang="bash">
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
</syntaxhighlight>
The system data will be in the rootfs partition and the data written to the root directory will be in the data partition.

==Restore Factory Settings With OverlayFS==
===Method 1: Operate in Userdata Partition===
factory reset:
<syntaxhighlight lang="bash">
mount /dev/mmcblk0p3 /media/ && cd /media/
mv root/ deleteme.root
mv work/ deleteme.work
reboot
</syntaxhighlight>
cleanup after reboot:
<syntaxhighlight lang="bash">
mount /dev/mmcblk0p3 /media/ && rm -rf /media/deleteme.*
</syntaxhighlight>
===Method 2: Restore by Setting Commandline Parameters===
===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;
====恢复出厂设置====
<syntaxhighlight lang="bash">
sudo fw_setenv bootargs "`sed 's/ wipedata=yes//g;s/ wipedata=no//g' /proc/cmdline` wipedata=yes"
sudo reboot
</syntaxhighlight>
====Keep Data in Data Partition on System Reboot====
<syntaxhighlight lang="bash">
sudo fw_setenv bootargs "`sed 's/ wipedata=yes//g;s/ wipedata=no//g' /proc/cmdline` wipedata=no"
sudo reboot
</syntaxhighlight>
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.
====RK3399 platform====
<syntaxhighlight lang="bash">
echo wipedata=yes > /var/.init_wipedata; sync; reboot
</syntaxhighlight>
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.
====H3/H5 platform====
=====change boot.cmd=====
Enter the boot directory and modify file boot.cmd, change the following:
<syntaxhighlight lang="bash">
setenv bootargs "console=${debug_port} earlyprintk
root=/dev/mmcblk0p2 rootfstype=ext4 rw rootwait fsck.repair=${fsck.repair}
panic=10 fbcon=${fbcon} ${hdmi_res} ${overlayfs} ${pmdown}"
</syntaxhighlight>
to:
<syntaxhighlight lang="bash">
setenv bootargs "console=${debug_port} earlyprintk
root=/dev/mmcblk0p2 rootfstype=ext4 rw rootwait fsck.repair=${fsck.repair}
panic=10 fbcon=${fbcon} ${hdmi_res} ${overlayfs} ${pmdown} wipedata=yes"
</syntaxhighlight>
Added wipedata=yes.
=====regenerate boot.scr=====
Enter the boot directory，execute the following command：
<syntaxhighlight lang="bash">
$ mkimage -C none -A arm -T script -d boot.cmd boot.scr
</syntaxhighlight>
==Disable OverlayFS==
If you have an installation TF card, use the fdisk command to delete the data partition.