Documentation for the script create_overlay_mount.sh

Last Update: 17.06.2025/bs

Documentation for the script create_overlay_mount.sh

Introduction

Since Android 10 many file systems in the Android OS are only mounted read-only and can no longer be mounted writable even by the root user. This is safe, but extremely unattractive.

One way to circumvent these restrictions is to install Magisk and Magisk modules. Magisk uses bind mounts to change or create files in the read-only file systems. This works very well to create or change binaries in /system/bin, for example. However, when creating the Magisk module you need to know which files are to be added or replaced.

To install new tools directly in Android via “make install”, for example, this does not work

A more flexible solution is the use of overlay mounts. As far as I know, overlay mounts have been supported in Android since Android 10 (at least partially).

For those who have Magisk installed, overlay mounts for the standard read-only directories can be created using the Magisk module

https://github.com/Magisk-Modules-Alt-Repo/magisk_overlayfs

That Magisk module also works perfectly in the Android 15.

(see How to create Magisk Modules that install new files in system for Details).

Because overlay mounts are supported by Android out-of-the-box, Magisk is not mandatory to use overlay mounts in Android.

Therefor I wrote a little script to manually create and use overlay mounts in Android on rooted devices:

create_overlay_mount.sh

The usage for the script is:

ASUS_I006D:/data/local/tmp $ ./create_overlay_mount.sh -h create_overlay_mount.sh - create one or more overlay mounts on a device running a rooted Android OS Usage: create_overlay_mount.sh [-h|--help] [--verbose|-v] [--noselinux] [--selinux] [--initdisk|--format] [--details] [--short] [--active] [var=value] [help] [vars] [list] [test] [undo] [diff] [get] [restore] [mount_only] [mount] [umount] [remount] [directory0] [... directory#] ASUS_I006D:/data/local/tmp #
To view the detailed usage help use the parameter -v -h or help:

./create_overlay_mount.sh help

ASUS_I006D:/data/local/tmp $ ./create_overlay_mount.sh help create_overlay_mount.sh - create one or more overlay mounts on a device running a rooted Android OS Usage: create_overlay_mount.sh [-h|--help] [--verbose|-v] [--noselinux] [--selinux] [--initdisk|--format] [--details] [--short] [--active] [var=value] [help] [vars] [list] [test] [undo] [diff] [get] [restore] [mount_only] [mount] [umount] [remount] [directory0] [... directory#] The parameter that neither start with a "-" or "/" nor contain a "=" are the action parameter that determine what is to be done. Only one action parameter for a run is allowed. Without an action parameter the script prints the short usage help. If one more directories are found in the parameter the default action is "mount". All parameter starting with a "/" are considered to be a filename or directory name. The parameter with the directory names are optional. The default directory list for the actions "mount", "diff", "get" and "undo" is the list of directories in the environment variable DIRS_TO_OVERLAY. The default directory list for the actions "test", "umount", and "remount" is the list of directories currently mounted to an overlay filesystem. There are no default values for the action "restore"; the actions "mount_only" and "list" ignore directory parameter. The actions "vars" and "help" only print help messages. If the variable DIRS_TO_OVERLAY is empty the script uses the hardcoded default value for this variable; that is: /system_ext /vendor /product /odm /system "directory#" must be either "default", "none", or the fully qualified directory name of a directory. The value "none" deletes the current list of directories in the variable DIRS_TO_OVERLAY; the value "default" adds the default directories to the list of directories.. The parameter can be used more than once. The known option parameter are: --verbose print more messages --noselinux disable SELinux at start of the script (SELinux is NOT enabled again by the script) --selinux enable SELinux at start of the script (SELinux is NOT disabled again by the script) --initdisk format the virtual disk before creating the overlay mounts; this will undo all previous changes in the filesystems Without this option the script never formats an existing virtual disk. --details print more details --short print only the important information --active the tasks diff, get, and undo work only on the currently mounted overlay filesystesm if this option is used The known action parameter are: help print verbose usage help vars print only the list of supported environment variables list list directories mounted on overlay filesystems test test write access to directories mounted on overlay filesystems; default is: test write access to all directories with mounted on overlay filesystems undo delete all changes done in a directory with an overlay mount default is: delete all changes done for all directories configured (regardless of the mount status) diff list the file changes for directories with overlay mounts default is: list the changes done for all directories configured (regardless of the mount status) get print the name of the backend used for a file or directory mounted on an overlay filesystem restore restore a file or directory mounted on an overlay filesystem mount_only mount the virtual disk and exit mount mount the overlays for the directories umount umount the overlays for the directories; default is to umount all overlays remount remount the overlay mounts Other supported parameter: var=value sets the variable "var" to the value "value" Notes Set the variable TRACE to any value before starting script execute it with "set -x" Supported environment variables: Name Default Value ---- ------------- IMAGE_FILE /data/local/tmp/image001 BASEDIR /data/local/tmp/ov DIRS_TO_OVERLAY /system_ext /vendor /product /odm /system FILESYSTEM_TO_USE ext4 FILESYSTEM_SIZE 100m MKFS_OPTIONS MOUNT_OPTIONS SELINUX_CONTEXT u:object_r:system_file:s0 ASUS_I006D:/data/local/tmp #

----

See the details below for usage examples of the script.

Author

Bernd Schemmer (Bernd.Schemmer@gmx.de)

LIcense

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History

ChangeLog

17.06.2025 /bs

Initial release

------

Details

The script must be executed by the root user to create the overlay mounts. In addition, root access is necessary to create or change files or directories in the system directories mounted to overlay mounts.

The filesystem type used for the filesystem mounted on /data does not support overlay mounts. Therefore, the script creates a file, configures that file as virtual disk, formats the virtual disk with the ext4 filesystem and mounts the virtual disk. The filesystem on the virtual disks is than used as backend for the overlay mounts. If the virtual disk already exists, the script uses it again without formating the virtual disk.

All changes in the directories mounted via overlay mounts are saved on the virtual disk. Therefore, the changes in the directories that are mounted via the overlay file system are persistent as long as the virtual disk used as the backend for the overlay mounts exists.

Overlay mounts can be created for most of the directories, except for directories in the filesystem mounted to /data and some directories with special meaning (like /dev, /sys, /proc detc.) or directories with special SELinux context like /oem.

If the script is executed without a parameter, the script prints the short usage help.

If there are one or more directories in the parameter but no action parameter, the default action is mount .

If the script is exeucted with an action parameter and one or more directories in the parameter, the requested action is done only for the directories in the parameter.

If the script is executed with an action parameter but without a directory, the action is done for the directories in the default directory list.

The default directory list used by the different actions are:

Action	Default directories	Comment
mount	directories listed in the environment variable DIRS_TO_OVERLAY
diff	directories listed in the environment variable DIRS_TO_OVERLAY	the action is done regardless of the mount status of the directories use the option --active to process only the mounted overlay filesystems
undo	directories listed in the environment variable DIRS_TO_OVERLAY	the action is done regardless of the mount status of the directories use the option --active to process only the mounted overlay filesystems

test	directories currently mounted with an overlay filesystem
umount	directories currently mounted with an overlay filesystem
remount	directories currently mounted with an overlay filesystem
get	directories listed in the environment variable DIRS_TO_OVERLAY	use the option --active to process only the mounted overlay filesystems

restore	n/a	there are no default files or directories for this action
list	n/a	The action always lists all directories currently mounted with an overlay filesystem Use the option --details to also list the backend directory and backend disk for each overlay mount
mount_only	n/a

To explicitly request one of the actions only for the directories listed in the variable DIRS_TO_OVERLAY, use the parameter default.

The default value for the variable DIRS_TO_OVERLAY hard-coded in the script is: /system_ext /vendor /product /odm /system

Usage examples

To create the overlay mounts, use the the script parameter mount.

Example output of executing the script with the parameter mount the first time:

/data/local/tmp/create_overlay_mount.sh mount

ASUS_I006D:/ # date Wed Jun 18 06:57:54 CEST 2025 ASUS_I006D:/ # ASUS_I006D:/ # id uid=0(root) gid=0(root) groups=0(root) context=u:r:magisk:s0 ASUS_I006D:/ # ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh create_overlay_mount.sh v1.0.0 - create one or more overlay mounts on a device running a rooted Android OS Usage: create_overlay_mount.sh [-h|--help] [--version] [--verbose|-v] [--noselinux] [--selinux] [--initdisk|--format] [--details] [--short] [--active] [var=value] [help] [vars] [list] [test] [undo] [diff] [get] [restore] [mount_only] [mount] [umount] [remount] [directory0] [... directory#] [default] ASUS_I006D:/ # ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh mount Creating the image file "/data/local/tmp/image001" with the size 100m ... 1+0 records in 1+0 records out 104857600 bytes (100 M) copied, 0.093 s, 1.0 G/s Creating the loop device for the file "/data/local/tmp/image001" .... Creating an "ext4" filesystem on the loop device "/dev/block/loop37" now ... mke2fs 1.46.6 (1-Feb-2023) Discarding device blocks: done Creating filesystem with 102400 1k blocks and 25584 inodes Filesystem UUID: 975b3b47-73af-4759-92bf-b83d80c5f85c Superblock backups stored on blocks: 8193, 24577, 40961, 57345, 73729 Allocating group tables: done Writing inode tables: done Creating journal (4096 blocks): done Writing superblocks and filesystem accounting information: done Mounting the loop device "/dev/block/loop37" to "/data/local/tmp/ov" ... Creating the directory "/data/local/tmp/ov/upper" ... Creating the directory "/data/local/tmp/ov/merged" ... Creating the directory "/data/local/tmp/ov/work" ... Creating and mounting the directories for the overlay mount for "/system_ext" ... Creating the directory "/data/local/tmp/ov/upper/system_ext" ... Creating the directory "/data/local/tmp/ov/merged/system_ext" ... Creating the directory "/data/local/tmp/ov/work/system_ext" ... Creating the overlay mount for "/system_ext" ... Creating the bind mount "/system_ext"... Checking the overlay mount for "/system_ext" ... Creating and mounting the directories for the overlay mount for "/vendor" ... Creating the directory "/data/local/tmp/ov/upper/vendor" ... Creating the directory "/data/local/tmp/ov/merged/vendor" ... Creating the directory "/data/local/tmp/ov/work/vendor" ... Creating the overlay mount for "/vendor" ... Creating the bind mount "/vendor"... Checking the overlay mount for "/vendor" ... Creating and mounting the directories for the overlay mount for "/product" ... Creating the directory "/data/local/tmp/ov/upper/product" ... Creating the directory "/data/local/tmp/ov/merged/product" ... Creating the directory "/data/local/tmp/ov/work/product" ... Creating the overlay mount for "/product" ... Creating the bind mount "/product"... Checking the overlay mount for "/product" ... Creating and mounting the directories for the overlay mount for "/odm" ... Creating the directory "/data/local/tmp/ov/upper/odm" ... Creating the directory "/data/local/tmp/ov/merged/odm" ... Creating the directory "/data/local/tmp/ov/work/odm" ... Creating the overlay mount for "/odm" ... Creating the bind mount "/odm"... Checking the overlay mount for "/odm" ... Creating and mounting the directories for the overlay mount for "/system" ... Creating the directory "/data/local/tmp/ov/upper/system" ... Creating the directory "/data/local/tmp/ov/merged/system" ... Creating the directory "/data/local/tmp/ov/work/system" ... Creating the overlay mount for "/system" ... Creating the bind mount "/system"... Checking the overlay mount for "/system" ... Summary: -------- 5 overlay mount(s) created: /system_ext /vendor /product /odm /system ASUS_I006D:/ #

---

To only create an overlay mount for the directory /odm_dlkm the script usage is

/data/local/tmp/create_overlay_mount.sh mount /odm_dlkm

or

/data/local/tmp/create_overlay_mount.sh /odm_dlkm

/data/local/tmp/create_overlay_mount.sh /odm_dlkm

ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh /odm_dlkm The image file "/data/local/tmp/image001" already exists - there should already be a filesystem Creating and mounting the directories for the overlay mount for "/odm_dlkm" ... Creating the directory "/data/local/tmp/ov/upper/odm_dlkm" ... Creating the directory "/data/local/tmp/ov/merged/odm_dlkm" ... Creating the directory "/data/local/tmp/ov/work/odm_dlkm" ... Creating the overlay mount for "/odm_dlkm" ... Creating the bind mount "/odm_dlkm"... Checking the overlay mount for "/odm_dlkm" ... Summary: -------- 1 overlay mount(s) created: /odm_dlkm ASUS_I006D:/ #

----

Further examples for the use of the script:

To list the overlay mounts created by the script use the parameter list :

/data/local/tmp/create_overlay_mount.sh list

ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh list Directories mounted on an overlay filesystem /system_ext /vendor /product /odm /system /odm_dlkm ASUS_I006D:/ # ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh list --details Directories mounted on an overlay filesystem Directory Backend Directory --------- ----------------- /system_ext /data/local/tmp/ov (Virtual disk: /data/local/tmp/image001) /vendor /data/local/tmp/ov (Virtual disk: /data/local/tmp/image001) /product /data/local/tmp/ov (Virtual disk: /data/local/tmp/image001) /odm /data/local/tmp/ov (Virtual disk: /data/local/tmp/image001) /system /data/local/tmp/ov (Virtual disk: /data/local/tmp/image001) ASUS_I006D:/ #

---

To test the write access in the directories with overlay mounts use the parameter test:

/data/local/tmp/create_overlay_mount.sh test

90|ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh test Testing the write access for directories mounted on overlay filesystems ... Testing write access for the directory "/system_ext" ... OK, the write access to the directory "/system_ext" works Testing write access for the directory "/vendor" ... OK, the write access to the directory "/vendor" works Testing write access for the directory "/product" ... OK, the write access to the directory "/product" works Testing write access for the directory "/odm" ... OK, the write access to the directory "/odm" works Testing write access for the directory "/system" ... OK, the write access to the directory "/system" works Testing write access for the directory "/odm_dlkm" ... OK, the write access to the directory "/odm_dlkm" works ASUS_I006D:/ #

---

To list the backend used for a file or directory use the parameter get:

./create_overlay_mount.sh get /system_ext/priv-app/OmniControl/testdir

ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh diff /system_ext List the changes in the directories ... ---------------------------------------------------------------------- List the changes in the directory "/system_ext" ... There is currently an overlay mounted for the directory "/system_ext" File changes in the directory "/system_ext" : ./priv-app ./priv-app/OmniControl ./priv-app/OmniControl/testdir ./priv-app/OmniControl/testdir/testdir2 ./priv-app/OmniControl/testdir/testdir2/testfile3 ./priv-app/OmniControl/testdir/testfile2 ./priv-app/OmniControl/testfile1 Files or directories deleted in the directory "/system_ext" : ./priv-app/OmniControl/oat/arm64/OmniControl.odex ./priv-app/OmniControl/oat/arm64/OmniControl.vdex ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh get /system_ext/priv-app/OmniControl/testdir /data/local/tmp/ov/upper/system_ext/priv-app/OmniControl/testdir # /system_ext/priv-app/OmniControl/testdir # the directory was changedASUS_I006D:/ # ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh get /system_ext/priv-app/OmniControl/testdir/testdir2 /data/local/tmp/ov/upper/system_ext/priv-app/OmniControl/testdir/testdir2 # /system_ext/priv-app/OmniControl/testdir/testdir2 # the directory was changedASUS_I006D:/ # ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh get /system_ext/priv-app/OmniControl/testdir/testdir2/testfile3 /data/local/tmp/ov/upper/system_ext/priv-app/OmniControl/testdir/testdir2/testfile3 # /system_ext/priv-app/OmniControl/testdir/testdir2/testfile3 # the file was changedASUS_I006D:/ # ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh get /system_ext/priv-app/OmniControl/testdir/testfile2 /data/local/tmp/ov/upper/system_ext/priv-app/OmniControl/testdir/testfile2 # /system_ext/priv-app/OmniControl/testdir/testfile2 # the file was changed ASUS_I006D:/ # ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh get /system_ext/priv-app/OmniControl/testfile1 /data/local/tmp/ov/upper/system_ext/priv-app/OmniControl/testfile1 # /system_ext/priv-app/OmniControl/testfile1 # the file was changed ASUS_I006D:/ # ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh get /system_ext/priv-app/OmniControl/testfile5 /data/local/tmp/ov/upper/system_ext/priv-app/OmniControl/testfile5 # /system_ext/priv-app/OmniControl/testfile5 # the file was not yet changed or deleted ASUS_I006D:/ #
ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh get /system_ext/priv-app/OmniControl/oat/arm64/OmniControl.odex
/data/local/tmp/ov/upper/system_ext/priv-app/OmniControl/oat/arm64/OmniControl.odex # the file/directory was deleted

ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh get /system_ext/priv-app/OmniControl/oat/arm64/OmniControl.vdex
/data/local/tmp/ov/upper/system_ext/priv-app/OmniControl/oat/arm64/OmniControl.vdex # the file/directory was deleted

ASUS_I006D:/ #

------

The options --short and --details can be used change the information printed by the action get:

Other example for get

ASUS_I006D:/data/local/tmp # ./create_overlay_mount.sh list Directories mounted on an overlay filesystem /odm/etc /vendor ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # /data/local/tmp/create_overlay_mount.sh diff /odm/etc /vendor List the changes in the directories ... ---------------------------------------------------------------------- List the changes in the directory "/odm/etc" ... There is currently an overlay mounted for the directory "/odm/etc" File changes in the directory "/odm/etc" : ./passwd ./selinux ./selinux/precompiled_sepolicy Files or directories deleted in the directory "/odm/etc" : ./group ---------------------------------------------------------------------- List the changes in the directory "/vendor" ... There is currently an overlay mounted for the directory "/vendor" File changes in the directory "/vendor" : ./etc ./etc/vmmgr.conf Files or directories deleted in the directory "/vendor" :
ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ./create_overlay_mount.sh get /vendor /vendor/etc /vendor/etc/vmmgr.conf /odm /odm/etc /odm/etc/passwd /odm/etc/group /vendor/etc/ueventd.rc /odm/etc/build.prop /data/local/tmp/ov/upper/vendor # /vendor # the directory was changed /data/local/tmp/ov/upper/vendor/etc # /vendor/etc # the directory was changed /data/local/tmp/ov/upper/vendor/etc/vmmgr.conf # /vendor/etc/vmmgr.conf # the file was changed # There is no overlay mount active for "/odm" /data/local/tmp/ov/upper/odm#etc # /odm/etc # the directory was changed /data/local/tmp/ov/upper/odm#etc/passwd # /odm/etc/passwd # the file was changed /data/local/tmp/ov/upper/odm#etc/group # the file/directory was deleted /data/local/tmp/ov/upper/vendor/etc/ueventd.rc # /vendor/etc/ueventd.rc # the file was not yet changed or deleted /data/local/tmp/ov/upper/odm#etc/build.prop # /odm/etc/build.prop # the file was not yet changed or deleted ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ./create_overlay_mount.sh get /vendor /vendor/etc /vendor/etc/vmmgr.conf /odm /odm/etc /odm/etc/passwd /odm/etc/group /vendor/etc/ueventd.rc /odm/etc/build.prop --short /data/local/tmp/ov/upper/vendor /data/local/tmp/ov/upper/vendor/etc /data/local/tmp/ov/upper/vendor/etc/vmmgr.conf # There is no overlay mount active for "/odm" /data/local/tmp/ov/upper/odm#etc /data/local/tmp/ov/upper/odm#etc/passwd /data/local/tmp/ov/upper/odm#etc/group /data/local/tmp/ov/upper/vendor/etc/ueventd.rc /data/local/tmp/ov/upper/odm#etc/build.propASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ./create_overlay_mount.sh get /vendor /vendor/etc /vendor/etc/vmmgr.conf /odm /odm/etc /odm/etc/passwd /odm/etc/group /vendor/etc/ueventd.rc /odm/etc/build.prop --details drwxr-xr-x 3 root shell u:object_r:vendor_file:s0 1024 2025-06-18 07:01 /data/local/tmp/ov/upper/vendor # /vendor # the directory was changed drwxr-xr-x 2 root shell u:object_r:vendor_configs_file:s0 1024 2025-06-18 09:04 /data/local/tmp/ov/upper/vendor/etc # /vendor/etc # the directory was changed -rw-r--r-- 1 root root u:object_r:vendor_configs_file:s0 25 2025-06-18 09:04 /data/local/tmp/ov/upper/vendor/etc/vmmgr.conf # /vendor/etc/vmmgr.conf # the file was changed # There is no overlay mount active for "/odm" drwxr-xr-x 3 root root u:object_r:vendor_configs_file:s0 1024 2025-06-18 09:05 /data/local/tmp/ov/upper/odm#etc # /odm/etc # the directory was changed -rw-r--r-- 1 root root u:object_r:vendor_configs_file:s0 7 2025-06-18 09:04 /data/local/tmp/ov/upper/odm#etc/passwd # /odm/etc/passwd # the file was changed c--------- 1 root root u:object_r:vendor_configs_file:s0 0, 0 2025-06-18 09:05 /data/local/tmp/ov/upper/odm#etc/group # the file/directory was deleted /data/local/tmp/ov/upper/vendor/etc/ueventd.rc # /vendor/etc/ueventd.rc # the file was not yet changed or deleted /data/local/tmp/ov/upper/odm#etc/build.prop # /odm/etc/build.prop # the file was not yet changed or deleted ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ./create_overlay_mount.sh get /vendor /vendor/etc /vendor/etc/vmmgr.conf /odm /odm/etc /odm/etc/passwd /odm/etc/group /vendor/etc/ueventd.rc /odm/etc/build.prop --details --short drwxr-xr-x 3 root shell u:object_r:vendor_file:s0 1024 2025-06-18 07:01 /data/local/tmp/ov/upper/vendor drwxr-xr-x 2 root shell u:object_r:vendor_configs_file:s0 1024 2025-06-18 09:04 /data/local/tmp/ov/upper/vendor/etc -rw-r--r-- 1 root root u:object_r:vendor_configs_file:s0 25 2025-06-18 09:04 /data/local/tmp/ov/upper/vendor/etc/vmmgr.conf # There is no overlay mount active for "/odm" drwxr-xr-x 3 root root u:object_r:vendor_configs_file:s0 1024 2025-06-18 09:05 /data/local/tmp/ov/upper/odm#etc -rw-r--r-- 1 root root u:object_r:vendor_configs_file:s0 7 2025-06-18 09:04 /data/local/tmp/ov/upper/odm#etc/passwd c--------- 1 root root u:object_r:vendor_configs_file:s0 0, 0 2025-06-18 09:05 /data/local/tmp/ov/upper/odm#etc/group /data/local/tmp/ov/upper/vendor/etc/ueventd.rc /data/local/tmp/ov/upper/odm#etc/build.prop ASUS_I006D:/data/local/tmp #

-----

To umount all overlay mounts created by the script use the parameter umount (Note that umounting /system fails in most cases due to open files and therefore, a reboot is necessary to umount /system):

/data/local/tmp/create_overlay_mount.sh umount

ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh umount Umounting the bind mounts ... Umounting "/system_ext" ... Umounting "/vendor" ... Umounting "/product" ... Umounting "/odm" ... Umounting "/system" ... umount: /system: Device or resource busy ... done Sleeping 8 seconds now ... Umounting the overlay mounts ... Umounting "/data/local/tmp/ov/merged/system_ext" ... Umounting "/data/local/tmp/ov/merged/vendor" ... Umounting "/data/local/tmp/ov/merged/product" ... Umounting "/data/local/tmp/ov/merged/odm" ... ... done 1|ASUS_I006D:/ #

---

To umount only the overlays of the directories /vendor and /odm use this command:

/data/local/tmp/create_overlay_mount.sh umount /vendor /odm

ASUS_I006D:/ #/data/local/tmp/create_overlay_mount.sh umount /vendor /odmUmounting the directories found in the parameter ...Umounting the bind mounts ...Umounting "/vendor" ...Umounting "/odm" ... ... doneSleeping 8 seconds now ...Umounting the overlay mounts ...Umounting "/data/local/tmp/ov/merged/vendor" ...Umounting "/data/local/tmp/ov/merged/odm" ... ... done ASUS_I006D:/ #

------

Note:

The sleep between umounting the bind mounts and umounting the overlay mounts seems to be necessary. The number of seconds to wait is defined in the variable UMOUNT_WAIT_TIME in the script.

To test another value for this variable use this Syntax:

/data/local/tmp/create_overlay_mount.sh umount UMOUNT_WAIT_TIME=<new_number_of_seconds>

If the new value is okay, change the value for UMOUNT_WAIT_TIME in the script.

To create an overlay mount for an additional directory, execute the script again, e.g. to create an additional overlay mount for the directory /vendor_dlkm/etc:

/data/local/tmp/create_overlay_mount.sh /vendor_dlkm/etc

ASUS_I006D:/data/local/tmp # /data/local/tmp/create_overlay_mount.sh /vendor_dlkm/etc The image file "/data/local/tmp/image001" already exists - there should already be a filesystem Creating and mounting the directories for the overlay mount for "/vendor_dlkm/etc" ... ERROR: "/vendor_dlkm/etc" is a symbolic link for "/vendor/vendor_dlkm/etc" -- ignored Summary: -------- 1 directory(s) missing: /vendor_dlkm/etc ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # /data/local/tmp/create_overlay_mount.sh /vendor/vendor_dlkm/etc The image file "/data/local/tmp/image001" already exists - there should already be a filesystem Creating and mounting the directories for the overlay mount for "/vendor/vendor_dlkm/etc" ... Creating the directory "/data/local/tmp/ov/upper/vendor#vendor_dlkm#etc" ... Creating the directory "/data/local/tmp/ov/merged/vendor#vendor_dlkm#etc" ... Creating the directory "/data/local/tmp/ov/work/vendor#vendor_dlkm#etc" ... Creating the overlay mount for "/vendor/vendor_dlkm/etc" ... Creating the bind mount "/vendor/vendor_dlkm/etc"... Checking the overlay mount for "/vendor/vendor_dlkm/etc" ... Summary: -------- 1 overlay mount(s) created: /vendor/vendor_dlkm/etc ASUS_I006D:/data/local/tmp # ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh list Directories mounted on overlay filesystem /system /system_ext /vendor /product /odm
/vendor/vendor_dlkm/etc ASUS_I006D:/ #

---

Directory parameters for the script overwrite the variable DIRS_TO_OVERLAY. To create an overlay mount for the default directories and additional directories, use the parameter default, e.g.: to create overlay mounts for the default directories and the directories /vendor_dlkm/etc and /odm_dlkm, execute:

/data/local/tmp/create_overlay_mount.sh default /vendor_dlkm/etc /odm_dlkm

ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh default /vendor_dlkm/etc /odm_dlkm Creating the loop device for the file "/data/local/tmp/image001" .... The image file already exists - there should already be a filesystem Mounting the loop device "/dev/block/loop31" to "/data/local/tmp/ov" ... Creating and mounting the directories for the overlay mount for "/system_ext" ... Creating the overlay mount for "/system_ext" ... Creating the bind mount "/system_ext"... Creating and mounting the directories for the overlay mount for "/vendor" ... Creating the overlay mount for "/vendor" ... Creating the bind mount "/vendor"... Creating and mounting the directories for the overlay mount for "/product" ... Creating the overlay mount for "/product" ... Creating the bind mount "/product"... Creating and mounting the directories for the overlay mount for "/odm" ... Creating the overlay mount for "/odm" ... Creating the bind mount "/odm"... Creating and mounting the directories for the overlay mount for "/system" ... Creating the overlay mount for "/system" ... Creating the bind mount "/system"... Creating and mounting the directories for the overlay mount for "/vendor_dlkm/etc" ... Creating the overlay mount for "/vendor_dlkm/etc" ... Creating the bind mount "/vendor_dlkm/etc"... Creating and mounting the directories for the overlay mount for "/odm_dlkm" ... Creating the overlay mount for "/odm_dlkm" ... Creating the bind mount "/odm_dlkm"... Summary: -------- 7 overlay mount(s) created: /system_ext /vendor /product /odm /system /vendor_dlkm/etc /odm_dlkm ASUS_I006D:/ #

----

To check the contents of the virtual disk used as backend without creating the overlay mounts use the parameter mount_only:

/data/local/tmp/create_overlay_mount.sh mount_only

# create some test files

ASUS_I006D:/ # for i in /system /system_ext /vendor /product /odm/ /vendor_dlkm/etc ; do touch $i/test.$$ ; ls -l $i/test.$$ ; done-rw-r--r-- 1 root root 0 2025-03-15 21:01 /system/test.5491-rw-r--r-- 1 root root 0 2025-03-15 21:01 /system_ext/test.5491-rw-r--r-- 1 root root 0 2025-03-15 21:01 /vendor/test.5491-rw-r--r-- 1 root root 0 2025-03-15 21:01 /product/test.5491-rw-r--r-- 1 root root 0 2025-03-15 21:01 /odm//test.5491-rw-r--r-- 1 root root 0 2025-03-15 21:01 /vendor_dlkm/etc/test.5491

# and reboot the phone

ASUS_I006D:/ # reboot
...

# execute in an adb shell after the reboot

ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh mount_onlyCreating the loop device for the file "/data/local/tmp/image001" ....The image file already exists - there should already be a filesystemMounting the loop device "/dev/block/loop31" to "/data/local/tmp/ov" ...The virtual disk is mounted to "/data/local/tmp/ov" ASUS_I006D:/ #

The new files are in the sub directory ./upper:
ASUS_I006D:/ # ls -l /data/local/tmp/ov/upper/*/*-rw-r--r-- 1 root root 0 2025-03-15 21:01 /data/local/tmp/ov/upper/odm/test.5491-rw-r--r-- 1 root root 0 2025-03-15 21:01 /data/local/tmp/ov/upper/product/test.5491-rw-r--r-- 1 root root 0 2025-03-15 21:01 /data/local/tmp/ov/upper/system/test.5491-rw-r--r-- 1 root root 0 2025-03-15 21:01 /data/local/tmp/ov/upper/system_ext/test.5491-rw-r--r-- 1 root root 0 2025-03-15 21:01 /data/local/tmp/ov/upper/vendor/test.5491-rw-r--r-- 1 root root 0 2025-03-15 21:01 /data/local/tmp/ov/upper/vendor_dlkm#etc/test.5491 ASUS_I006D:/ #

---

To create a new virtual disk /data/local/tmp/image001_ext3 with 50 MB and ext3 filesystem withoud creating any overlay filesystem use this command:

/data/local/tmp/create_overlay_mount.sh IMAGE_FILE=/data/local/tmp/image001_ext3 FILESYSTEM_TO_USE=ext3 FILESYSTEM_SIZE=50m mount_only

ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh IMAGE_FILE=/data/local/tmp/image001_ext3 FILESYSTEM_TO_USE=ext3 FILESYSTEM_SIZE=50m mount_onlyCreating the image file "/data/local/tmp/image001_ext3" with the size 50m ...1+0 records in1+0 records out52428800 bytes (50 M) copied, 0.072 s, 694 M/sCreating the loop device for the file "/data/local/tmp/image001_ext3" ....Creating an "ext3" filesystem on the loop device "/dev/block/loop37" now ...mke2fs 1.46.6 (1-Feb-2023)128-byte inodes cannot handle dates beyond 2038 and are deprecatedDiscarding device blocks: done Creating filesystem with 51200 1k blocks and 12824 inodesFilesystem UUID: 709aad6f-53d0-4a2a-adc6-c230fb7f283dSuperblock backups stored on blocks: 8193, 24577, 40961Allocating group tables: done Writing inode tables: done Creating journal (4096 blocks): doneWriting superblocks and filesystem accounting information: doneMounting the loop device "/dev/block/loop37" to "/data/local/tmp/ov" ...The virtual disk is mounted to "/data/local/tmp/ov" ASUS_I006D:/ # ASUS_I006D:/ # ls -alZ /data/local/tmp/ov total 17 drwxr-xr-x 3 root root u:object_r:system_file:s0 1024 2025-06-14 10:57 . drwxrwx--x 9 shell shell u:object_r:shell_data_file:s0 3452 2025-06-14 10:57 .. drwx------ 2 root root u:object_r:unlabeled:s0 12288 2025-06-14 10:57 lost+found ASUS_I006D:/ # ASUS_I006D:/ # df -h /data/local/tmp/ov Filesystem Size Used Avail Use% Mounted on /dev/block/loop37 44M 31K 44M 1% /data/local/tmp/ov ASUS_I006D:/ # 130|ASUS_I006D:/ # mount | grep /data/local/tmp/ov /dev/block/loop37 on /data/local/tmp/ov type ext3 (rw,seclabel,relatime) ASUS_I006D:/ # ASUS_I006D:/ # ls -lZh /data/local/tmp/image001_ext3 -rw-r--r-- 1 root root u:object_r:shell_data_file:s0 50M 2025-06-14 11:01 /data/local/tmp/image001_ext3 ASUS_I006D:/ #

------

To use the file /data/local/tmp/image001_ext3 for overlay mounts later use:

/data/local/tmp/create_overlay_mount.sh IMAGE_FILE=/data/local/tmp/image001_ext3 /vendor /vendor_dlkm/

ASUS_I006D:/ # /data/local/tmp/create_overlay_mount.sh IMAGE_FILE=/data/local/tmp/image001_ext3 /vendor /vendor_dlkm/The image file already exists - there should already be a filesystemCreating the directory "/data/local/tmp/ov/upper" ...Creating the directory "/data/local/tmp/ov/merged" ...Creating the directory "/data/local/tmp/ov/work" ...Creating and mounting the directories for the overlay mount for "/vendor" ...Creating the directory "/data/local/tmp/ov/upper/vendor" ...Creating the directory "/data/local/tmp/ov/merged/vendor" ...Creating the directory "/data/local/tmp/ov/work/vendor" ...Creating the overlay mount for "/vendor" ...Creating the bind mount "/vendor"...Checking the overlay mount for "/vendor" ...Creating and mounting the directories for the overlay mount for "/vendor_dlkm/" ...Creating the directory "/data/local/tmp/ov/upper/vendor_dlkm" ...Creating the directory "/data/local/tmp/ov/merged/vendor_dlkm" ...Creating the directory "/data/local/tmp/ov/work/vendor_dlkm" ...Creating the overlay mount for "/vendor_dlkm" ...Creating the bind mount "/vendor_dlkm"...Checking the overlay mount for "/vendor_dlkm" ...Summary:--------2 overlay mount(s) created: /vendor /vendor_dlkmASUS_I006D:/ #

To use different virtual disks in parallel the variable BASEDIR must also be different:

Example for using multiple virtual disks

ASUS_I006D:/data/local/tmp # IMAGE_FILE=/data/local/tmp/virtualdisk001 BASEDIR=/data/local/tmp/virtualfs001 ./create_overlay_mount.sh /vendor /vendor_dlkm Creating the image file "/data/local/tmp/virtualdisk001" with the size 100m ... 1+0 records in 1+0 records out 104857600 bytes (100 M) copied, 0.091 s, 1.0 G/s Creating the loop device for the file "/data/local/tmp/virtualdisk001" .... Creating an "ext4" filesystem on the loop device "/dev/block/loop37" now ... mke2fs 1.46.6 (1-Feb-2023) 128-byte inodes cannot handle dates beyond 2038 and are deprecated Discarding device blocks: done Creating filesystem with 102400 1k blocks and 25688 inodes Filesystem UUID: 2e0dbca9-6030-44a1-bff5-49d6a0c4f152 Superblock backups stored on blocks: 8193, 24577, 40961, 57345, 73729 Allocating group tables: done Writing inode tables: done Creating journal (4096 blocks): done Writing superblocks and filesystem accounting information: done Creating the directory "/data/local/tmp/virtualfs001" ... Mounting the loop device "/dev/block/loop37" to "/data/local/tmp/virtualfs001" ... Creating the directory "/data/local/tmp/virtualfs001/upper" ... Creating the directory "/data/local/tmp/virtualfs001/merged" ... Creating the directory "/data/local/tmp/virtualfs001/work" ... Creating and mounting the directories for the overlay mount for "/vendor" ... Creating the directory "/data/local/tmp/virtualfs001/upper/vendor" ... Creating the directory "/data/local/tmp/virtualfs001/merged/vendor" ... Creating the directory "/data/local/tmp/virtualfs001/work/vendor" ... Creating the overlay mount for "/vendor" ... Creating the bind mount "/vendor"... Checking the overlay mount for "/vendor" ... Creating and mounting the directories for the overlay mount for "/vendor_dlkm" ... Creating the directory "/data/local/tmp/virtualfs001/upper/vendor_dlkm" ... Creating the directory "/data/local/tmp/virtualfs001/merged/vendor_dlkm" ... Creating the directory "/data/local/tmp/virtualfs001/work/vendor_dlkm" ... Creating the overlay mount for "/vendor_dlkm" ... Creating the bind mount "/vendor_dlkm"... Checking the overlay mount for "/vendor_dlkm" ... Summary: -------- 2 overlay mount(s) created: /vendor /vendor_dlkm ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # IMAGE_FILE=/data/local/tmp/virtualdisk002 BASEDIR=/data/local/tmp/virtualfs002 ./create_overlay_mount.sh /odm /odm_dlkm SELinux is currently enabled Creating the image file "/data/local/tmp/virtualdisk002" with the size 100m ... 1+0 records in 1+0 records out 104857600 bytes (100 M) copied, 0.094 s, 1.0 G/s Creating the loop device for the file "/data/local/tmp/virtualdisk002" .... Creating an "ext4" filesystem on the loop device "/dev/block/loop38" now ... mke2fs 1.46.6 (1-Feb-2023) 128-byte inodes cannot handle dates beyond 2038 and are deprecated Discarding device blocks: done Creating filesystem with 102400 1k blocks and 25688 inodes Filesystem UUID: b7e73573-093d-4038-8efa-c7f3975b8932 Superblock backups stored on blocks: 8193, 24577, 40961, 57345, 73729 Allocating group tables: done Writing inode tables: done Creating journal (4096 blocks): done Writing superblocks and filesystem accounting information: done Creating the directory "/data/local/tmp/virtualfs002" ... Mounting the loop device "/dev/block/loop38" to "/data/local/tmp/virtualfs002" ... Creating the directory "/data/local/tmp/virtualfs002/upper" ... Creating the directory "/data/local/tmp/virtualfs002/merged" ... Creating the directory "/data/local/tmp/virtualfs002/work" ... Creating and mounting the directories for the overlay mount for "/odm" ... Creating the directory "/data/local/tmp/virtualfs002/upper/odm" ... Creating the directory "/data/local/tmp/virtualfs002/merged/odm" ... Creating the directory "/data/local/tmp/virtualfs002/work/odm" ... Creating the overlay mount for "/odm" ... Creating the bind mount "/odm"... Checking the overlay mount for "/odm" ... Creating and mounting the directories for the overlay mount for "/odm_dlkm" ... Creating the directory "/data/local/tmp/virtualfs002/upper/odm_dlkm" ... Creating the directory "/data/local/tmp/virtualfs002/merged/odm_dlkm" ... Creating the directory "/data/local/tmp/virtualfs002/work/odm_dlkm" ... Creating the overlay mount for "/odm_dlkm" ... Creating the bind mount "/odm_dlkm"... Checking the overlay mount for "/odm_dlkm" ... Summary: -------- 2 overlay mount(s) created: /odm /odm_dlkm ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ./create_overlay_mount.sh list --details Directories mounted on an overlay filesystem Directory Backend Directory --------- ----------------- /vendor /data/local/tmp/virtualfs001 (Virtual disk: /data/local/tmp/virtualdisk001) /vendor_dlkm /data/local/tmp/virtualfs001 (Virtual disk: /data/local/tmp/virtualdisk001) /odm /data/local/tmp/virtualfs002 (Virtual disk: /data/local/tmp/virtualdisk002) /odm_dlkm /data/local/tmp/virtualfs002 (Virtual disk: /data/local/tmp/virtualdisk002) ASUS_I006D:/data/local/tmp #

------

Note that in this case you must always use BASEDIR=<base_directory> and, for some commands IMAGE_FILE=<image_file>, to process the overlay mounts (e.g. for the actions undo, umount, diff, etc). Therefore it's recommended to create different wrapper scripts for using multiple virtual disks.

This feature can be used for example to create different test environments.

The script can also be used to create overlay mounts for sub directories, e.g. to create overlay filesystems for the directories /*/bin and the directory /system_ext/usr/share do

/data/local/tmp/create_overlay_mount.sh /*/bin /system_ext/usr/share

ASUS_I006D:/data/local/tmp # /data/local/tmp/create_overlay_mount.sh /*/bin /system_ext/usr/share The image file already exists - there should already be a filesystem Creating and mounting the directories for the overlay mount for "/product/bin" ... Creating the directory "/data/local/tmp/ov/upper/product#bin" ... Creating the directory "/data/local/tmp/ov/merged/product#bin" ... Creating the directory "/data/local/tmp/ov/work/product#bin" ... Creating the overlay mount for "/product/bin" ... Creating the bind mount "/product/bin"... Creating and mounting the directories for the overlay mount for "/system/bin" ... There is already an overlay mount for the directory "/system/bin" in place Creating and mounting the directories for the overlay mount for "/system_ext/bin" ... Creating the directory "/data/local/tmp/ov/upper/system_ext#bin" ... Creating the directory "/data/local/tmp/ov/merged/system_ext#bin" ... Creating the directory "/data/local/tmp/ov/work/system_ext#bin" ... Creating the overlay mount for "/system_ext/bin" ... Creating the bind mount "/system_ext/bin"... Creating and mounting the directories for the overlay mount for "/vendor/bin" ... Creating the directory "/data/local/tmp/ov/upper/vendor#bin" ... Creating the directory "/data/local/tmp/ov/merged/vendor#bin" ... Creating the directory "/data/local/tmp/ov/work/vendor#bin" ... Creating the overlay mount for "/vendor/bin" ... Creating the bind mount "/vendor/bin"... Creating and mounting the directories for the overlay mount for "/system_ext/usr/share" ... Creating the directory "/data/local/tmp/ov/upper/system_ext#usr#share" ... Creating the directory "/data/local/tmp/ov/merged/system_ext#usr#share" ... Creating the directory "/data/local/tmp/ov/work/system_ext#usr#share" ... Creating the overlay mount for "/system_ext/usr/share" ... Creating the bind mount "/system_ext/usr/share"... Summary: -------- 4 overlay mount(s) created: /product/bin /system_ext/bin /vendor/bin /system_ext/usr/share 1 overlay mount(s) already created: /system/bin ASUS_I006D:/data/local/tmp #

------

To list the file changes for a directory with overlay mount use the parameter diff, e.g. to list all changes for the directories /odm_dlkm and /system:

./create_overlay_mount.sh diff /odm_dlkm /system

90|ASUS_I006D:/data/local/tmp # ./create_overlay_mount.sh diff /odm_dlkm /system List the changes in the directories ... ---------------------------------------------------------------------- List the changes in the directory "/odm_dlkm" ... There is currently an overlay mounted for the directory "/odm_dlkm" File changes in the directory "/odm_dlkm" : ./testdir ./testdir/testfile1 ./testdir/testfile2 ./testfile0 Files or directories deleted in the directory "/odm_dlkm" : ./etc ---------------------------------------------------------------------- List the changes in the directory "/system" ... There is currently no overlay mounted for the directory "/system" File changes in the directory "/system" : ./bin ./bin/0001logcatboot ./bin/configure_microg.sh ./bin/correct_dev_pn553.sh ./bin/disable_intent_filter_verification.sh ./bin/enable_microg.sh ./bin/enable_wifi.sh ./bin/enable_wireless_adb.sh ./bin/install_apk.sh ./bin/install_mm.sh ./bin/list_bind_mounts.sh ./bin/list_logical_device_backends.sh ./bin/list_logical_device_usage.sh ./bin/list_magisk_root_permissions.sh ./bin/list_magisk_settings.sh ./bin/lmm ./bin/myldd ./bin/rcbm.sh ./bin/recreate_bind_mount.sh ./bin/remount_dynamic_partitions.sh ./bin/remove_screenlock.sh ./bin/rename_apk.sh ./bin/search_magisk_package.sh ./bin/setpath.sh ./bin/sudo ./bin/switch_adb_via_wifi.sh Files or directories deleted in the directory "/system" : ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ./create_overlay_mount.sh diff /odm_dlkm /system --details SELinux is currently enabled List the changes in the directories ... ---------------------------------------------------------------------- List the changes in the directory "/odm_dlkm" ... There is currently an overlay mounted for the directory "/odm_dlkm" File changes in the directory "/odm_dlkm" : drwxr-xr-x 3 root root u:object_r:vendor_file:s0 1024 2025-06-17 08:59 ./testdir -rw-r--r-- 1 root root u:object_r:vendor_file:s0 0 2025-06-17 08:59 ./testdir/testfile1 drwxr-xr-x 2 root root u:object_r:vendor_file:s0 1024 2025-06-17 09:00 ./testdir/testfile2 -rw-r--r-- 1 root root u:object_r:vendor_file:s0 0 2025-06-17 09:00 ./testfile0 Files or directories deleted in the directory "/odm_dlkm" : ./etc ---------------------------------------------------------------------- List the changes in the directory "/system" ... There is currently no overlay mounted for the directory "/system" File changes in the directory "/system" : drwxr-x--x 2 root shell u:object_r:system_file:s0 1024 2025-06-16 21:04 ./bin -rwxr-xr-x 1 root root u:object_r:system_file:s0 156 2025-06-16 21:04 ./bin/0001logcatboot -rwxr-xr-x 1 root root u:object_r:system_file:s0 2919 2025-06-16 21:04 ./bin/configure_microg.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 354 2025-06-16 21:04 ./bin/correct_dev_pn553.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 51 2025-06-16 21:04 ./bin/disable_intent_filter_verification.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 146 2025-06-16 21:04 ./bin/enable_microg.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 2956 2025-06-16 21:04 ./bin/enable_wifi.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 22230 2025-06-16 21:04 ./bin/enable_wireless_adb.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 10108 2025-06-16 21:04 ./bin/install_apk.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 16046 2025-06-16 21:04 ./bin/install_mm.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 4432 2025-06-16 21:04 ./bin/list_bind_mounts.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 7271 2025-06-16 21:04 ./bin/list_logical_device_backends.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 9463 2025-06-16 21:04 ./bin/list_logical_device_usage.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 223 2025-06-16 21:04 ./bin/list_magisk_root_permissions.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 449 2025-06-16 21:04 ./bin/list_magisk_settings.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 19701 2025-06-16 21:04 ./bin/lmm -rwxr-xr-x 1 root root u:object_r:system_file:s0 1038 2025-06-16 21:04 ./bin/myldd lrwxrwxrwx 1 root root u:object_r:system_file:s0 24 2025-06-16 21:04 ./bin/rcbm.sh -> ./recreate_bind_mount.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 3774 2025-06-16 21:04 ./bin/recreate_bind_mount.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 16866 2025-06-16 21:04 ./bin/remount_dynamic_partitions.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 69 2025-06-16 21:04 ./bin/remove_screenlock.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 2708 2025-06-16 21:04 ./bin/rename_apk.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 1434 2025-06-16 21:04 ./bin/search_magisk_package.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 42 2025-06-16 21:04 ./bin/setpath.sh -rwxr-xr-x 1 root root u:object_r:system_file:s0 13 2025-06-16 21:04 ./bin/sudo -rwxr-xr-x 1 root root u:object_r:system_file:s0 5273 2025-06-16 21:04 ./bin/switch_adb_via_wifi.sh Files or directories deleted in the directory "/system" : ASUS_I006D:/data/local/tmp #

----

The default directory list for the action diff is the list of directories in the variable DIRS_TO_OVERLAY. Use the options --active to list only the changes in all mounted overlay filesystems:

./create_overlay_mount.sh diff --active

----

To undo all changes for a directory with an overlay mount use the parameter undo, e.g. to undo all changes in the directory /system execute:

/create_overlay_mount.sh undo /system

ASUS_I006D:/data/local/tmp # ./create_overlay_mount.sh undo /systemUndoing the change in the directories ...Undoing the changes for the directory "/system" ...ASUS_I006D:/data/local/tmp #

------

To undo all the changes for all directories currently mounted on overlay filesystems do:

./create_overlay_mount.sh undo

ASUS_I006D:/data/local/tmp # ./create_overlay_mount.sh undoUndoing the change in the directories ...Undoing the changes for the directory "/system_ext" ...Undoing the changes for the directory "/vendor" ...Undoing the changes for the directory "/product" ...Undoing the changes for the directory "/odm" ...Undoing the changes for the directory "/system" ...ASUS_I006D:/data/local/tmp #

------

Note that there is no redo.

To undo the changes only for specific files use the parameter restore:

./create_overlay_mount.sh restore /system/etc/hosts

|ASUS_I006D:/data/local/tmp # cat /system/etc/hosts127.0.0.1 localhost::1 ip6-localhostASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # echo "1.1.1.1 dnsserver" >>/system/etc/hostsASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # cat /system/etc/hosts 127.0.0.1 localhost::1 ip6-localhost1.1.1.1 dnsserverASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ./create_overlay_mount.sh restore /system/etc/hostsDeleting the files "/data/local/tmp/ov/upper/system/etc/hosts" and "/data/local/tmp/ov/merged/system/etc/hosts" ...Restoring the file "/system/etc/hosts" ...ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # cat /system/etc/hosts127.0.0.1 localhost::1 ip6-localhostASUS_I006D:/data/local/tmp #

To restore a deleted file on a filesystem mount with overlays use the parameter restore :

./create_overlay_mount.sh restore /odm/etc/build.prop

ASUS_I006D:/data/local/tmp # ls -l /odm/etc/build.prop-rw------- 1 root root 999 2009-01-01 01:00 /odm/etc/build.propASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # rm /odm/etc/build.propASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ls -l /odm/etc/build.propls: /odm/etc/build.prop: No such file or directory1|ASUS_I006D:/data/local/tmp # 1|ASUS_I006D:/data/local/tmp # ./create_overlay_mount.sh restore /odm/etc/build.propRestoring the file "/odm/etc/build.prop" ...ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ls -l /odm/etc/build.prop-rw------- 1 root root 999 2009-01-01 01:00 /odm/etc/build.propASUS_I006D:/data/local/tmp #

------

In case of an error in a directory with an overlay you may remount the directory using the script parameter remount:

./create_overlay_mount.sh remount /vendor

ASUS_I006D:/data/local/tmp # ./create_overlay_mount.sh remount /vendorRemounting the bind mounts ...Remounting "/vendor" ... ... doneASUS_I006D:/data/local/tmp #

------

Environment variables used by the script

The script uses these environment variables:

Variable	Usage	Default value	Comment
IMAGE_FILE	file used for the virtual disk	/data/local/tmp/image001
BASEDIR	the mount point for the virtual disk	/data/local/tmp/ov
DIRS_TO_OVERLAY	the directories for which the script creates an overlay mount	/system_ext /vendor /product /odm /system
FILESYSTEM_TO_USE	the filesystem used on the virtual disk	ext4	must be a filesystem known by the running Android that supports overlay mounts (e.g. ext4 or ext3) The parameter is only used when creating a new filesystem on the virtual disk.
FILESYSTEM_SIZE	the size of the virtual disk	100m	the value can be any value that is known by the binary dd for the parameter bs (see the output of "`dd --help`") The variable is only used when the virtual disk is created.
MKFS_OPTIONS	additional options for the mkfs* command to create the filesysten on the loop device		The variable is only used when the virtual disk is created.
MOUNT_OPTIONS	additional options for the mount command to mount the filesystem on the loop device
SELINUX_CONTEXT	the SELinux context used for new directories if the script can not read the SELinux context of an existing directory	u:object_r:system_file:s0

To change one or more of these variables use either a command like this

IMAGE_FILE="/data/local/tmp/image002" BASEDIR="/data/local/tmp/ov2" create_overlay_mount.sh

or this

create_overlay_mount.sh IMAGE_FILE="/data/local/tmp/image002" BASEDIR="/data/local/tmp/ov2"

Note:

Use

create_overlay_mount.sh vars

to only print the current list of supported environment variables with default values.

The new files created in the directories with overlay mounts can be found in the directory

${BASEDIR}/upper/${DIR_NAME}

e.g.

ASUS_I006D:/data/local/tmp # df -h /odm Filesystem      Size Used Avail Use% Mounted on overlay          93M 71K   93M   1% /odm ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # touch /odm/testfile.$$ ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ls -l /odm/testfile.$$                                                                                    -rw-r--r-- 1 root root 0 2025-06-14 14:13 /odm/testfile.7172 ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ls -l /data/local/tmp/ov/upper/odm/testfile.7172 -rw-r--r-- 1 root root 0 2025-06-14 14:13 /data/local/tmp/ov/upper/odm/testfile.7172 ASUS_I006D:/data/local/tmp #

For sub directories with overlay mounts the directory name in the directory ${BASEDIR}/upper is in the format subir1#subdir2#....#subdirN,

For an overlay mount for /vendor/etc the directory name is vendor#etc:

ASUS_I006D:/data/local/tmp # df -h /vendor Filesystem      Size Used Avail Use% Mounted on /dev/block/dm-4 0.9G 983M   29M 98% /vendor ASUS_I006D:/data/local/tmp #                                                                                                           ASUS_I006D:/data/local/tmp # df -h /vendor/etc Filesystem      Size Used Avail Use% Mounted on overlay          93M 76K   93M   1% /vendor/etc ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # touch /vendor/etc/testfile.$$ ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ls -l /vendor/etc/testfile.$$                                                                             -rw-r--r-- 1 root root 0 2025-06-14 14:15 /vendor/etc/testfile.7172 ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ls -l /data/local/tmp/ov/upper/vendor\#etc/testfile.7172                                                  -rw-r--r-- 1 root root 0 2025-06-14 14:15 /data/local/tmp/ov/upper/vendor#etc/testfile.7172 ASUS_I006D:/data/local/tmp #

For deleted files or directories a character device with major 0 and minor 0 is created in the directory ./upper, e.g:

ASUS_I006D:/data/local/tmp # rm /vendor/etc/ueventd.rc                                                                                 ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ls -l /vendor/etc/ueventd.rc                                                                              ls: /vendor/etc/ueventd.rc: No such file or directory 1|ASUS_I006D:/data/local/tmp # 1|ASUS_I006D:/data/local/tmp # ls -l /data/local/tmp/ov/upper/vendor\#etc/ueventd.rc                                                   c--------- 1 root root 0,   0 2025-06-14 14:17 /data/local/tmp/ov/upper/vendor#etc/ueventd.rc ASUS_I006D:/data/local/tmp #

ext3 and ext4 filesystems can be increased while mounted:

Instructions to increase the virtual disk used as backend

# Note: only the commands in bold are necessary to increase the virtual disk ASUS_I006D:/ # ls -lh /data/local/tmp/image001 -rw-r--r-- 1 root root 10M 2025-03-15 20:36 /data/local/tmp/image001 ASUS_I006D:/ # # -> the size of the file used as virtual disk is 10 MB ASUS_I006D:/ # df -h /data/local/tmp/ov Filesystem Size Used Avail Use% Mounted on /dev/block/loop31 8.6M 39K 8.6M 1% /data/local/tmp/ov ASUS_I006D:/ # # increase the size of the file /data/local/tmp/image001 by 50M ASUS_I006D:/ # dd if=/dev/zero count=1 bs=50m >>/data/local/tmp/image001 1+0 records in 1+0 records out 52428800 bytes (50 M) copied, 0.058147 s, 860 M/s ASUS_I006D:/ # ASUS_I006D:/ # ls -lh /data/local/tmp/image001 -rw-r--r-- 1 root root 60M 2025-03-15 20:38 /data/local/tmp/image001 ASUS_I006D:/ #
# -> the size of the file used as virtual disk is now 60 MB # update the loop device # ASUS_I006D:/ # losetup -j /data/local/tmp/image001 -c ASUS_I006D:/ # # resize the filesystem on the virtual disk # ASUS_I006D:/ # resize2fs /dev/block/loop31 resize2fs 1.46.2 (28-Feb-2021) Filesystem at /dev/block/loop31 is mounted on /data/local/tmp/ov; on-line resizing required old_desc_blocks = 1, new_desc_blocks = 1 The filesystem on /dev/block/loop31 is now 61440 (1k) blocks long. ASUS_I006D:/ # ASUS_I006D:/ # df -h /data/local/tmp/ov Filesystem Size Used Avail Use% Mounted on /dev/block/loop31 58M 39K 58M 1% /data/local/tmp/ov ASUS_I006D:/ #

Note:

ext4 filesystem can also be decreased when the filesystem is not mounted but it is not that easy to shrink the file used for the virtual disk.

----

Notes

Run the script only in an adb session as root user -- do not execute it via "su - -c ...." (after creating an overlay mount for /system, the binary su is not available anymore!)

For first tests, I strongly recommend NOT to create an overlay mount for the directory /system:

If something fails when creating an overlay for /system, there is no access to any of the executables and files in /system anymore and a reboot via Android GUI is required to fix that

The script does not support directory names with a hash "#" in the name.

To check, if overlay filesystems are supported in the Android OS use the command:

grep overlay /proc/filesystems

The output should look like this:

ASUS_I006D:/data/local/tmp # grep overlay /proc/filesystemsnodev overlayASUS_I006D:/data/local/tmp #

Please note that files created with Magisk modules, e.g. in /system/bin, are no longer visible after configuring an overlay mount for /system using the script create_overlay_mount.sh. That's also true for the executable "su" necessary to become root user if Magisk is installed. Therefore, either open enough adb sessions with root access before doing the overlay mount for /system or use a CustomROM with enabled root access.

You can copy the files from the Magisk module to /system after creating an overlay mount for that directory, example

Copy the files from the Magisk module myscripts to /system:

cp -r /data/adb/modules/myscripts/system/* /system

Another way to work around the problem of the missing su command is to start the sshd as root user on the phone before creating the overlay mount for /system.

Or use a Magisk Module to start the adb daemon as root user (see here)
https://xdaforums.com/t/how-to-automatically-start-adbd-as-root-user-after-starting-the-phone.4682701/

If Magisk is installed, I recommend using the Magisk module for the implementation of overlay mounts, as the overlay mounts are created very early in the boot process in the Magisk module. The overlay mounts created by the Magisk module also do not overwrite bind mounts created by other Magisk modules and "su" via Magisk is still possible in adb sessions when using this Magisk module.

Do not use the Magisk module for the implementation of overlay mounts and the script create_overlay_mount.sh in parallel.

create_overlay_mount.sh can be used to mount the virtual disk used by the Magisk Module for overlay mounts, /data/adb/modules/magisk_overlayfs/overlay.img, but the directory structure on that virtual disk is different and therefore the virtual disk should not be used to create overlay mounts with create_overlay_mount.sh .

Details

ASUS_I006D:/data/local/tmp # IMAGE_FILE=/data/adb/modules/magisk_overlayfs/overlay.img ./create_overlay_mount.sh mount_only SELinux is currently enabled Creating the loop device for the file "/data/adb/modules/magisk_overlayfs/overlay.img" .... The image file "/data/adb/modules/magisk_overlayfs/overlay.img" already exists - there should already be a filesystem Mounting the loop device "/dev/block/loop37" to "/data/local/tmp/ov" ... The virtual disk is mounted to "/data/local/tmp/ov" ASUS_I006D:/data/local/tmp # ASUS_I006D:/data/local/tmp # ls -ld $( find /data/local/tmp/ov ) drwxr-xr-x 4 root root 1024 2025-06-16 21:10 /data/local/tmp/ov drwx------ 2 root root 12288 2025-06-16 21:10 /data/local/tmp/ov/lost+found drwxr-xr-x 3 root root 1024 2025-06-16 21:10 /data/local/tmp/ov/system drwxr-xr-x 2 root root 1024 2025-06-16 21:10 /data/local/tmp/ov/system/bin lrwxrwxrwx 1 root root 18 2025-06-16 21:10 /data/local/tmp/ov/system/bin/magic_remount_ro -> ./overlayfs_system lrwxrwxrwx 1 root root 18 2025-06-16 21:10 /data/local/tmp/ov/system/bin/magic_remount_rw -> ./overlayfs_system -rwxrwxrwx 1 root root 6960576 2025-06-16 21:10 /data/local/tmp/ov/system/bin/overlayfs_system ASUS_I006D:/data/local/tmp #

------

Test Environment

ASUS Zenfone 8 with

/e/ 3.0 (= Android 13)
LineageOS 20 (= Android 13)
LineageOS 21 (= Android 14)
OmniROM 14 (= Android 14)
OmniROM 15 (= Android 15)

Note:

According to ChatGPT this functionality does not work on all Android versions (but ChatGTP is sometimes also a great liar ...)

Trouble Shooting

An overlay mount for sub directories like /system_ext/bin or /system/etc may or may not work.

If it does not work, the files in the sub directory with overlay mount do not have any permission, example:

ASUS_I006D:/data/local/tmp # ls -ldZ /system_ext/bin/*---------- 1 root root u:object_r:unlabeled:s0 0 1970-01-04 04:35 /system_ext/bin/adb_rootlrwxrwxrwx 1 root root u:object_r:unlabeled:s0 16 1970-01-04 04:35 /system_ext/bin/bash -> /system/bin/bash---------- 1 root root u:object_r:unlabeled:s0 0 1970-01-04 04:35 /system_ext/bin/dpmdlrwxrwxrwx 1 root root u:object_r:unlabeled:s0 3 1970-01-04 04:35 /system_ext/bin/eview -> vimlrwxrwxrwx 1 root root u:object_r:unlabeled:s0 3 1970-01-04 04:35 /system_ext/bin/evim -> vimlrwxrwxrwx 1 root root u:object_r:unlabeled:s0 3 1970-01-04 04:35 /system_ext/bin/ex -> vimlrwxrwxrwx 1 root root u:object_r:unlabeled:s0 3 1970-01-04 04:35 /system_ext/bin/gview -> vimlrwxrwxrwx 1 root root u:object_r:unlabeled:s0 3 1970-01-04 04:35 /system_ext/bin/gvim -> vimlrwxrwxrwx 1 root root u:object_r:unlabeled:s0 3 1970-01-04 04:35 /system_ext/bin/gvimdiff -> vim---------- 1 root root u:object_r:unlabeled:s0 0 1970-01-04 04:35 /system_ext/bin/htop---------- 1 root root u:object_r:unlabeled:s0 0 1970-01-04 04:35 /system_ext/bin/nano...
create_overlay_mount.sh prints a warning in this case, example:

WARNING: Seems like the overlay mount for "/system_ext/bin" works only partial -- please check the directory contents

To work around this problem, create an overlay mount for the upper directory (e.g. /system or /system_ext) -- at least in my tests, overlay mounts for these directories have always worked.

In my tests on the different Android versions there were always such errors, but not for the same subdirectories. There is no error message in logcat or dmesg, so I don't know the reason for this error yet.

Use the script parameter -v or --verbose to print more messages

Set the variable TRACE to any string before executing the script to run it with "set -x"

Most problems with overlay mounts are caused by missing or invalid SELinux contexts for the files and directories for which an overlay mount is configured. It is therefore recommended to
temporarily disable SELinux either by using the command

setenforce 0

or use the script parameter "--noselinux"

Start a parallel adb session with the command

logcat | grep denied

or, on the PC, :

adb logcat | grep denied

while testing the overlay mounts.

Links

The Linux Kernel - overlay filesystems

How to use Overlay FS?