Difference between revisions of "How to use overlayfs on Linux"

Revision as of 03:00, 7 May 2021

查看中文

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平台设置下次开机时抹掉data分区的数据(即恢复出厂设置)

echo wipedata=yes > /var/.init_wipedata; sync; reboot

下次启动到ramdisk阶段，会对data分区进行格式化，/var/.init_wipedata 文件也会被清除。

6 Disable OverlayFS

If you have an installation TF card, use the fdisk command to delete the data partition.