I've mentioned this elsewhere in some of my howtos, but I think this feature is important and useful enough to get its own howto.
Nowadays in the current Android OS version a lot filesystems are mounted read-only and remounting the filesystem read-write does not work anymore. Therefor the files in these filesystems can not be changed anymore.
That's pretty good from a safety standpoint, but sometimes a real showstopper.
But fortunately Android is a Linux based system and therefor there is a solution for this problem called bind mounts. bind mounts are some kind of symbolic links that only exist in memory and are therefor also supported for read-only mounted filesystems. Of course, this is a very simple description for this Linux feature but it should be enough here -- for more in depth details I recommend the Linux documentation.
bind mounts are used by Magisk but they can also be used manually without an installed Magisk - the only requirement for using it manually is root access to the phone.
Here is an example to replace the file /system/etc/hosts with a writable file using a bind mount:
Spoiler: replace the file /system/etc/hosts with a changed version of the file
Code:
#
# use a filesystem that supports all necessary permissions and attributes for the new file
#
# Therefor files in /sdcard/<something> can not be used to replace most of the files in the read-only filesystems
#
# Make sure that the file used to replace the other file is readable by all user that can also read the original file
#
ASUS_I006D:/ # cp -a /system/etc/hosts /data/local/tmp/my_hosts
ASUS_I006D:/ #
# add some additional data to the new file
#
ASUS_I006D:/ # echo "127.0.0.1 www.heise.de" >>/data/local/tmp/my_hosts
ASUS_I006D:/ #
# check the result
#
ASUS_I006D:/ # cat /data/local/tmp/my_hosts
127.0.0.1 localhost
::1 ip6-localhost
127.0.0.1 www.heise.de
ASUS_I006D:/ #
ASUS_I006D:/ # ls -l /system/etc/hosts /data/local/tmp/my_hosts
-rw-r--r-- 1 root root 80 2023-06-11 14:57 /data/local/tmp/my_hosts
-rw-r--r-- 1 root root 56 2009-01-01 01:00 /system/etc/hosts
ASUS_I006D:/ #
# "replace" the file /system/etc/hosts now
#
ASUS_I006D:/ # su - -c mount -o bind /data/local/tmp/my_hosts /system/etc/hosts
ASUS_I006D:/ #
# check the results
#
ASUS_I006D:/ # cat /system/etc/hosts
127.0.0.1 localhost
::1 ip6-localhost
127.0.0.1 www.heise.de
ASUS_I006D:/ #
# add some more data to the file
#
ASUS_I006D:/ # echo "127.0.0.1 www.spiegle.de" >>/system/etc/hosts
ASUS_I006D:/ #
# check the result
#
ASUS_I006D:/ # cat /system/etc/hosts
127.0.0.1 localhost
::1 ip6-localhost
127.0.0.1 www.heise.de
127.0.0.1 www.spiegle.de
ASUS_I006D:/ #
bind mounts are only possible for existing files - bind mounts for non-existent files will fail, e.g:
Spoiler: Example for a bind mount for an non-existent file
Code:
ASUS_I006D:/ $ ls /system/bin/bash
ls: /system/bin/bash: No such file or directory
1|ASUS_I006D:/ $
1|ASUS_I006D:/ $ su - -c mount -o bind /system/bin/sh /system/bin/bash
mount: '/system/bin/sh'->'/system/bin/bash': No such file or directory
1|ASUS_I006D:/ $
bind mounts are also allowed for directories therefor to "create" a new file just copy the directory, create the new file in that new directory, and then do a bind mount for the existing directory.
Example:
Spoiler: create the executable bash by copying the executable sh
Code:
#
# "create" the executable "bash" by copying the executable "sh"
#
# This is only an example that should work on every phone! In real life you should copy a real bash executable to the new directory
#
#
# check for a bash executable in the PATH
#
ASUS_I006D:/ $ which bash
1|ASUS_I006D:/ $
# -> bash does currently not exist on the phone
# create a new directory to be used for the bind mount /system/xbin
#
# Note that this directory must be on a filesystem supporting the standard linux file permissions therefor a directory in /sdcard/<something> is not possible here
# And again the directory used must be readable by all uesrs.
#
ASUS_I006D:/ $ mkdir /data/local/tmp/xbin
ASUS_I006D:/ $
# copy all files from /system/xbin to the new directory
#
ASUS_I006D:/ $ su - -c cp -a -r /system/xbin/* /data/local/tmp/xbin
ASUS_I006D:/ $
ASUS_I006D:/ $ ls -l /data/local/tmp/xbin
total 1772
lrwxrwxrwx 1 root shell 3 2009-01-01 01:00 vi -> vim
-rwxr-xr-x 1 root shell 1813848 2009-01-01 01:00 vim
ASUS_I006D:/ $
# create fake "bash" executable in the new directory
#
ASUS_I006D:/ $ cp /system/bin/sh /data/local/tmp/xbin/bash
ASUS_I006D:/ $
ASUS_I006D:/ $ ls -l /data/local/tmp/xbin
total 2080
-rwxr-xr-x 1 shell shell 312024 2023-06-11 13:56 bash
lrwxrwxrwx 1 root shell 3 2009-01-01 01:00 vi -> vim
-rwxr-xr-x 1 root shell 1813848 2009-01-01 01:00 vim
ASUS_I006D:/ $
# bind mount the directory /system/xbin on the new directory
#
ASUS_I006D:/ $ su - -c mount -o bind /data/local/tmp/xbin /system/xbin
ASUS_I006D:/ $
# and now there is "bash" executable in /system/xbin available
#
ASUS_I006D:/ $ ls -l /system/xbin
total 2080
-rwxr-xr-x 1 shell shell 312024 2023-06-11 13:56 bash
lrwxrwxrwx 1 root shell 3 2009-01-01 01:00 vi -> vim
-rwxr-xr-x 1 root shell 1813848 2009-01-01 01:00 vim
ASUS_I006D:/ $ which bash
/system/xbin/bash
# You can now even copy additional files to the bind mounted directory, e.g.:
ASUS_I006D:/ $ cp /sdcard/Download/zip /system/xbin
ASUS_I006D:/ $
ASUS_I006D:/ $ chmod 755 /system/xbin/zip
ASUS_I006D:/ $
ASUS_I006D:/ $ ls -ltr /system/xbin
total 2576
-rwxr-xr-x 1 root shell 1813848 2009-01-01 01:00 vim
lrwxrwxrwx 1 root shell 3 2009-01-01 01:00 vi -> vim
-rwxr-xr-x 1 shell shell 312024 2023-06-11 13:56 bash
-rwxr-xr-x 1 shell shell 503992 2023-06-11 14:03 zip
ASUS_I006D:/ $
ASUS_I006D:/ $ zip -h
Copyright (c) 1990-2008 Info-ZIP - Type 'zip "-L"' for software license.
Zip 3.0 (July 5th 2008). Usage:
zip [-options] [-b path] [-t mmddyyyy] [-n suffixes] [zipfile list] [-xi list]
The default action is to add or replace zipfile entries from list, which
can include the special name - to compress standard input.
If zipfile and list are omitted, zip compresses stdin to stdout.
-f freshen: only changed files -u update: only changed or new files
-d delete entries in zipfile -m move into zipfile (delete OS files)
-r recurse into directories -j junk (don't record) directory names
-0 store only -l convert LF to CR LF (-ll CR LF to LF)
-1 compress faster -9 compress better
-q quiet operation -v verbose operation/print version info
-c add one-line comments -z add zipfile comment
[email protected] read names from stdin -o make zipfile as old as latest entry
-x exclude the following names -i include only the following names
-F fix zipfile (-FF try harder) -D do not add directory entries
-A adjust self-extracting exe -J junk zipfile prefix (unzipsfx)
-T test zipfile integrity -X eXclude eXtra file attributes
-y store symbolic links as the link instead of the referenced file
-e encrypt -n don't compress these suffixes
-h2 show more help
Hints
bind mounts are supported by the filesystems ext4, vfat, f2fs. and most probably a lot of other filesystems used on machines running Android.
Be careful when replacing executables, especially when replacing an important file like /system/bin/sh. And you should never replace a file that is just a symbolic link for toybox or busybox.
bind mounts created while the OS is running are only useful for files that are dynamically read by the OS. It does not make sense to replace for example one of the *.rc files using a bind mount because these files are only read once while booting the OS.
The filesystems used for source and target for a bind mount should support the same set of attributes and permissions or the result may not be like expected. E.g. you can not bind mount an executable with a file in the directory /sdcard/<something> because that filesystem for /sdcard does not support the executable permission:
Spoiler: Example for bind mount an executable in /sdcard/Download
Code:
ASUS_I006D:/ $ ls -l /bin/ziptool
-rwxr-xr-x 1 root shell 28688 2009-01-01 01:00 /bin/ziptool
ASUS_I006D:/ $
ASUS_I006D:/ $ cp -a /bin/ziptool /sdcard/Download/
ASUS_I006D:/ $
ASUS_I006D:/ $ chmod 755 /sdcard/Download/ziptool
ASUS_I006D:/ $
ASUS_I006D:/ $ ls -l /bin/ziptool /sdcard/Download/ziptool
-rwxr-xr-x 1 root shell 28688 2009-01-01 01:00 /bin/ziptool
-rw-rw---- 1 u0_a121 media_rw 28688 2023-06-11 18:09 /sdcard/Download/ziptool
ASUS_I006D:/ $
ASUS_I006D:/ $ su - -c mount -o bind /sdcard/Download/ziptool /bin/ziptool
ASUS_I006D:/ $
ASUS_I006D:/ $ ziptool
/system/bin/sh: ziptool: can't execute: Permission denied
126|ASUS_I006D:/ $ /bin/ziptool
/system/bin/sh: /bin/ziptool: can't execute: Permission denied
126|ASUS_I006D:/ $ ls -l /bin/ziptool
-rw-rw---- 1 u0_a121 media_rw 28688 2023-06-11 18:09 /bin/ziptool
ASUS_I006D:/ $
The source for the bind mount must be in a directory that is readable for all user that use the bind mounted file, e.g.
Spoiler: Example for bind mount an executable in a directory not accessable by all user
Code:
ASUS_I006D:/ $ su - -c cp -a /bin/ziptool /data/adb/ziptool
ASUS_I006D:/ $
ASUS_I006D:/ $ su - -c ls -l /data/adb/ziptool
-rwxr-xr-x 1 root shell 28688 2009-01-01 01:00 /data/adb/ziptool
ASUS_I006D:/ $
ASUS_I006D:/ $ su - -c mount -o bind /data/adb/ziptool /bin/ziptool
ASUS_I006D:/ $
ASUS_I006D:/ $ ziptool
/system/bin/sh: ziptool: inaccessible or not found
127|ASUS_I006D:/ $
127|ASUS_I006D:/ $ file /bin/ziptool
/bin/ziptool: cannot open: Permission denied
ASUS_I006D:/ $
Use the mount command to check if a file is bind mounted. e.g.
Spoiler: Check if a file is bind mounted
Code:
|ASUS_I006D:/ # mount | grep /system/etc/hosts
1|ASUS_I006D:/ #
1|ASUS_I006D:/ # mount -o bind /data/local/tmp/hosts /system/etc/hosts
ASUS_I006D:/ #
ASUS_I006D:/ # mount | grep /system/etc/hosts
/dev/block/dm-33 on /system/etc/hosts type f2fs (rw,lazytime,seclabel,nosuid,nodev,noatime,background_gc=on,discard,no_heap,user_xattr,inline_xattr,acl,inline_data,inline_dentry,flush_merge,extent_cache,mode=adaptive,active_logs=6,reserve_root=32768,resuid=0,resgid=1065,inlinecrypt,alloc_mode=default,fsync_mode=nobarrier)
ASUS_I006D:/ #
To remove a bind mount just do a umount, e.g:
Spoiler: Example for remove a bind mount
Code:
#
# remove the bind mount
#
ASUS_I006D:/ $ su - -c umount /bin/ziptool
ASUS_I006D:/ $
ASUS_I006D:/ $ which ziptool
/system/bin/ziptool
ASUS_I006D:/ $ ziptool
ziptool: run as ziptool with unzip or zipinfo as the first argument, or symlink
1|ASUS_I006D:/ $
Another method to remove all bind mounts is a reboot of the phone
It's recommended to use a sub directory in the directory /data/local/tmp for executables used in bind mounts, example:
Spoiler: Example for bind mount an executable in /data/local/tmp/
Code:
ASUS_I006D:/ $ mkdir /data/local/tmp/bind_mounts
ASUS_I006D:/ $
ASUS_I006D:/ $ cp -a /bin/ziptool /data/local/tmp/bind_mounts
ASUS_I006D:/ $
ASUS_I006D:/ $ ls -l /data/local/tmp/bind_mounts/ziptool
-rwxr-xr-x 1 shell shell 28688 2009-01-01 01:00 /data/local/tmp/bind_mounts/ziptool
ASUS_I006D:/ $
ASUS_I006D:/ $ su - -c mount -o bind /data/local/tmp/bind_mounts/ziptool /bin/ziptool
ASUS_I006D:/ $
ASUS_I006D:/ $ ziptool
ziptool: run as ziptool with unzip or zipinfo as the first argument, or symlink
1|ASUS_I006D:/ $
bind mounts are also useful for writable files to be able to revert the changes to a file. Example:
Spoiler: Example for using bind mount for a writable file
Code:
ASUS_I006D:/ $ cat /data/local/tmp/testfile.txt
This is a test file
ASUS_I006D:/ $
#
# create a copy of the writable file
#
ASUS_I006D:/ $ cat /data/local/tmp/testfile_for_tests.txt
This is another test file
#
# bind mount the file with the copy of the file
#
ASUS_I006D:/ $ su - -c mount -o bind /data/local/tmp/testfile_for_tests.txt /data/local/tmp/testfile.txt
ASUS_I006D:/ $
#
# check the result
#
ASUS_I006D:/ $ cat /data/local/tmp/testfile.txt
This is another test file
ASUS_I006D:/ $
#
# add some data to the bind mounted file now
#
ASUS_I006D:/ $ echo "This text will not change the original file" >> /data/local/tmp/testfile.txt
ASUS_I006D:/ $
ASUS_I006D:/ $ cat /data/local/tmp/testfile.txt
This is another test file
This text will not change the original file
ASUS_I006D:/ $
#
# remove the bind mount to restore the original file contents
#
ASUS_I006D:/ $ su - -c umount /data/local/tmp/testfile.txt
ASUS_I006D:/ $
ASUS_I006D:/ $ cat /data/local/tmp/testfile.txt
This is a test file
ASUS_I006D:/ $
Of course, this can also be done by creating a backup copy of the file and restoring the backup copy if necessary. But if the changes to the file make the phone unusable or cause it to crash, it is more difficult to restore the file. If you use a bind mount, the file will be restored "automatically" at the next reboot.
Notes
see the forum entry How to upgrade the OS with another Android "distribution" for an example usage for this method
See the forum entry How To change any file or directory using Magisk for how to use this method in Magisk module for persisent changes
See the forum entry How to make files in /system writable for another exampe how to use this feature in Magisk
Up to version 25.x of Magisk (at least in Magisk v24.x and v25.x) Magisk mounted the /system/bin directory read-write, so that temporary changes for the files in /system/bin were possible. But because of the more or less not existent free space in the filesystem used for /system the use of this feature was very limited. And this feature does not exist in Magisk v26.x or newer anymore.
(see also this forum message: https://forum.xda-developers.com/t/magisk-general-support-discussion.3432382/page-2815#post-88617909 )
Related
Hello everybody,
I rooted my dream phone with :
Code:
fastboot boot boot.img
# mount -o remount,rw -t yaffs2 /dev/block/mtdblock3 /system
# cd system
# cd bin
# cat sh > su
# chmod 4755 su
All work fine !
I tried to install busybox like this :
Code:
adb push busybox /data/local/tmp
cat /data/local/tmp/busybox > /system/bin/busybox
chmod 4755 /system/bin/busybox
No problem with this step, but now if I type :
Code:
$su
#busybox ls /data
I have a permission denied
If I type
Code:
$su
#ls /data
all work fine
(ls is an symbolic link to toolbox)
ls -l /system/bin
Code:
-rwsr-xr-x root root 1745016 2009-07-28 11:01 busybox
-rwsr-xr-x root root 86936 2009-07-28 11:11 su
-rwxr-xr-x root shell 68472 2009-03-03 22:31 toolbox
...
I think busybox is not launch with root permission.. why?
I tried : ln -s busybox ls
but same problem !
What is wrong ?
Thanks.
Any particular reason why you setuid busybox? Try chmod 0755 busybox; chown root:shell busybox
I FINALY FOUND MY PROBLEM
I have two binaries one in /system/xbin/su and the other in /system/bin/su
#ls -l /system/*/su gives me this:
-rwxrwxr- system sdcard_rw 380532 2013-05-22 17:13 su
-rwsr-xr-x root root 22236 2013-05-22 17:13 su
#chmod 06775 /system/bin/su gives me this:
unable to chmod /system/bin/su: readonly filesystem
#echo $PATH gives me this
/system/bin/su: /system/Xbin/su
so what should i do next?
is it possible to swap the path variables
i mean to make "echo $path give /system/Xbin/su:/system/bin/su"
10Q
GAEENG said:
I FINALY FOUND MY PROBLEM
I have two binaries one in /system/xbin/su and the other in /system/bin/su
#ls -l /system/*/su gives me this:
-rwxrwxr- system sdcard_rw 380532 2013-05-22 17:13 su
-rwsr-xr-x root root 22236 2013-05-22 17:13 su
#chmod 06775 /system/bin/su gives me this:
unable to chmod /system/bin/su: readonly filesystem
#echo $PATH gives me this
/system/bin/su: /system/Xbin/su
so what should i do next?
is it possible to swap the path variables
i mean to make "echo $path give /system/Xbin/su:/system/bin/su"
10Q
Click to expand...
Click to collapse
Switch to SuperSU!
How to backup the data from the phone using rsync and ssh (including some hints for using sshd on an Android phone)
Like for all computer it's important to have a backup of the data on the phone.
For those who like me don't like to store their private data in one of the suspicious clouds there is a solution with standard Linux tools:
Use rsync and ssh to backup the data from the phone to your local workstation (see the man page for rsync for details regarding rsync and why it is useful for this task)
The neccessary tools for Android for this method can be installed with the Magisk Module MagiskSSH.
Download the Magisk Module with MagiskSSH from here
https://gitlab.com/d4rcm4rc/MagiskSSH_releases
Copy the ZIP file with the Magisk Module to the phone :
Code:
adb push magisk_ssh_v0.14.zip /sdcard/Download/
and install it via the module installation from within the Magisk App or manuell using :
Code:
adb shell su - -c /data/adb/magisk/magisk64 --install-module /sdcard/Download/magisk_ssh_v0.14.zip
Sample output of the installation:
Code:
ASUS_I006D:/ # /data/adb/magisk/magisk64 --install-module /sdcard/Download/magisk_ssh_v0.14.zip
- Current boot slot: _a
- Device is system-as-root
*******************************
OpenSSH for Android
*******************************
[0/7] Preparing module directory
[1/7] Extracting architecture unspecific module files
[2/7] Extracting libraries and binaries for arm64
[3/7] Configuring library path wrapper
[4/7] Recreating symlinks
[5/7] Creating SSH user directories
[6/7] Found sshd_config, will not copy a default one
[7/7] Cleaning up
- Setting permissions
- Done
ASUS_I006D:/ #
A reboot is required now.
Code:
adb shell reboot
For the next tasks open an adb shell and become root user.
Next create the authorized_keys file for the user root :
Code:
touch /data/ssh/root/.ssh/authorized_keys
chmod 600 /data/ssh/root/.ssh/authorized_keys
and add your public ssh key to the file /data/ssh/root/.ssh/authorized_keys.
To make sure that the keys and other data files for the MagiskSSH module are not removed while deinstalling the module you should create the file /data/ssh/KEEP_ON_UNINSTALL:
Code:
touch /data/ssh/KEEP_ON_UNINSTALL
The MagiskSSH module also installs a service to start sshd after each reboot: to disable this start create the file /data/ssh/no-autostart:
Code:
touch /data/ssh/no-autostart
To manually start or stop the sshd use the script /data/adb/modules/ssh/opensshd.init :
Code:
# start the sshd (as user root)
#
/data/adb/modules/ssh/opensshd.init start
# to stop the sshd (as user root)
#
/data/adb/modules/ssh/opensshd.init stop
Now test the access via ssh from your Linux workstation:
Code:
ssh -l root <phone_ip_address> id
Use this command to retrieve the current IP address of the phone:
Code:
PHONE_IP_ADDRESS=$( adb shell ifconfig wlan0 | grep "inet addr:" | sed -e "s/.*inet addr://g" -e "s/[[:space:]]*Bcast.*//g" )
example :
Code:
[[email protected] ~]$ ssh -l root ${PHONE_IP_ADDRESS} id
uid=0(root) gid=0(root) groups=0(root) context=u:r:magisk:s0
[[email protected] ~]$
Now you can use rsync to backup the data from the phone, e.g. to backup the photos from the phone do :
Code:
# on your local Linux workstation do:
# start the sshd on the phone via adb if not already running
#
adb shell su - -c /data/adb/modules/ssh/opensshd.init start
# retrieve the current IP address from the phone
#
PHONE_IP_ADDRESS=$( adb shell ifconfig wlan0 | grep "inet addr:" | sed -e "s/.*inet addr://g" -e "s/[[:space:]]*Bcast.*//g" )
# backup the new photos from the phone to the Linux workstation (rsync only copies new files from the phone)
# to the local directory /data/backup/ASUS_ZENFONE8/DCIM
#
rsync -av --rsync-path /data/adb/modules/ssh/usr/bin/rsync [email protected]${PHONE_IP_ADDRESS}:/sdcard/DCIM/ /data/backup/ASUS_ZENFONE8/DCIM
# optional stop the sshd on the phone via adb
#
adb shell su - -c /data/adb/modules/ssh/opensshd.init stop
Note: The sshd configuration file used is /data/ssh/sshd_config
Sample Script to backup all data in the directory /sdcard
Code:
##!/bin/bash
#
# simple script to backup the data of an phone using adb, ssh, and rsync
#
# History
# 27.06.2022 /bs
# initial release
#
# for testing
#
#RSYNC_OPTIONS="${RSYNC_OPTIONS} --dry-run"
RSYNC_OPTIONS="${RSYNC_OPTIONS} --del "
# default is to backup the phone connected via adb over LAN
#
[ $# -ne 0 ] && ADB_OPTIONS="$*" || ADB_OPTIONS="-e"
# retrieve the serial number of the attached phone
#
SERIAL_NO="$( adb ${ADB_OPTIONS} shell getprop ro.serialno )"
if [ "${SERIAL_NO}"x = ""x ] ; then
echo "ERROR: Can not read the serial number of the connected phone"
exit 89
fi
VENDOR_MODEL="$( adb ${ADB_OPTIONS} shell getprop ro.product.vendor.model )"
# directory for the backup
#
BACKUP_DIR="/data/backup/ASUS_ZENFONE8/data_backup/${VENDOR_MODEL}_${SERIAL_NO}"
if [ ! -d "${BACKUP_DIR}" ] ; then
echo "ERROR: The directory \"${BACKUP_DIR}\" does not exist"
exit 99
fi
PHONE_IP_ADDRESS="$( adb ${ADB_OPTIONS} shell ifconfig wlan0 | grep "inet addr:" | sed -e "s/.*inet addr://g" -e "s/[[:space:]]*Bcast.*//g" )"
if [ "${PHONE_IP_ADDRESS}"x = ""x ] ; then
echo "ERROR: Can not detect the IP address of the phone"
exit 100
fi
echo "Updating a backup of the data on the phone with the serial number \"${SERIAL_NO}\" and the IP \"${PHONE_IP_ADDRESS}\" to the directory \"${BACKUP_DIR}\" ..."
set -x
# start the sshd if neccessary
#
adb ${ADB_OPTIONS} shell su - -c /data/adb/modules/ssh/opensshd.init start
# do the backup
#
time rsync ${RSYNC_OPTIONS} -av --rsync-path /data/adb/modules/ssh/usr/bin/rsync [email protected]${PHONE_IP_ADDRESS}:/sdcard/ "${BACKUP_DIR}/"
# stop the sshd
#
adb ${ADB_OPTIONS} shell su - -c /data/adb/modules/ssh/opensshd.init stop
set +x
How to enable access via ssh for non-root user
In the standard configuration installed by MagiskSSH ssh access is only allowed as user root because the ssh keys are in the directory /data and all non-root user can not read files in the directory /data. Therefor some efforts are neccessary to add ssh access for non-root user.
e.g. To enable the ssh access for the user shell do:
To configure ssh access for the user shell we must create a .ssh directory for the user shell in a directory tree owned by the user shell. The only directory on the phone owned by the user shell that can be used for this purpose is /storage :
Code:
ASUS_I006D:/ # ls -ld /storage
drwx--x--- 4 shell everybody 80 2022-06-26 18:37 /storage
ASUS_I006D:/ #
But unfortunately all files and directories in this directory are temporary and will be deleted after a reboot of the phone.
Therefor we configure a startup script in Magisk to create this directory tree after each reboot, e.g.
/data/adb/service.d/create_ssh_dir_for_shell.sh:
Code:
# /data/adb/service.d/create_ssh_dir_for_shell.sh
#
mkdir -p /storage/shell/.ssh
chmod -R 700 /storage/shell/
touch /storage/shell/.ssh/authorized_keys
echo "<ssh_public_key>" > /storage/shell/.ssh/authorized_keys
chmod 600 /storage/shell/.ssh/authorized_keys
chown -R shell:shell /storage/shell
Make the script executable:
Code:
su - -c chmod +x data/adb/service.d/create_ssh_dir_for_shell.sh
To test the script just execute it one time manually as user root.
Code:
su - -c sh data/adb/service.d/create_ssh_dir_for_shell.sh
Now create a backup of the sshd config file
Code:
su - -c cp /data/ssh/sshd_config /storage/ssh/sshd_config.org.$$
and add these lines at the end of the file /data/ssh/sshd_config
Code:
Match User shell
AuthorizedKeysFile /storage/shell/.ssh/authorized_keys
Restart the sshd if it's already running
Now test the access as user shell, example:
Code:
[[email protected] ~]$ ssh -l shell 192.168.1.148 id
uid=2000(shell) gid=2000(shell) groups=2000(shell) context=u:r:magisk:s0
[[email protected] ~]$
The reason for this config is the setting "StrictMode yes" in the sshd config file /data/ssh/sshd_config (see the man page for sshd_config for details). So another "solution" is to change this setting:
With the setting "StrictModes no" in the file sshd_config the directory with the authorized_keys file for the non-root users can be anywhere (for example in /sdcard/shell)
Execute as user root:
Code:
sed -i -e "s/.*StrictModes.*//g" -e "s/UsePrivilegeSeparation/StrictModes no\nUsePrivilegeSeparation/g" /data/ssh/sshd_config
and change the entry in the file /data/ssh/sshd_config for the authorized_keys file for the user shell, for example:
Code:
Match User shell
AuthorizedKeysFile /sdcard/shell/.ssh/authorized_keys
Afterwards restart the sshd:
Code:
/data/adb/modules/ssh/opensshd.init stop
/data/adb/modules/ssh/opensshd.init start
Now create the directories and files neccessary for the ssh access (see above) in the directory /sdcard/shell:
Code:
SUS_I006D:/ # find /sdcard/shell -exec ls -ld {} \;
drwxrws--- 3 u0_a118 media_rw 3452 2022-06-26 18:32 /sdcard/shell
drwxrws--- 2 u0_a118 media_rw 3452 2022-06-26 18:32 /sdcard/shell/.ssh
-rw-rw---- 1 u0_a118 media_rw 408 2022-06-26 18:32 /sdcard/shell/.ssh/authorized_keys
ASUS_I006D:/ #
and the access as user shell via ssh should work
How to run a script at shutdown
To define additional startup scripts via Magisk the Magisk directories /data/adb/service.d and /data/adb/post-fs-data.d can be used. Unfortunately there is no equivalent for scripts that should be executed during shutdown.
So we must use other methods to implement these kind of scripts.
Using the overlay feature of Magisk to run a script at shutdown
Introduction
in Android it is possible to define actions that will be executed when certain conditions are satisfied.
These definitions are done in the file init.rc (and other .rc files) using the Android Init Language.
And this feature can be used to execute a command when the phone is shutting down.
Note:
For details about the Android Init Language used for these files see here https://android.googlesource.com/platform/system/core/+/master/init/README.md
The .rc files used by Android are in the directories
/system/etc/init/vendor/etc/init/odm/etc/init
Note: The first .rc file read is /system/etc/init/hw/init.rc
Unfortunately it's useless to change the .rc files in these directories using the Magisk features to change files in the directory /system because these files are processed by the OS before the new files are "created" by Magisk.
Therefor the overlay functionality from Magisk must be used to create additional .rc files (see the section Root Directory Overlay System on this page https://github.com/topjohnwu/Magisk/blob/master/docs/guides.md for details about this Magisk Feature).
Preparation
To be able to restore the original boot partition in case of an error create an image of the original boot partition from the phone on your PC before starting the development:
Code:
CUR_SLOT=$( adb shell getprop ro.boot.slot_suffix )
adb shell su - -c dd if=/dev/block/by-name/boot${CUR_SLOT} | cat >boot${CUR_SLOT}
e.g.
Code:
[ OmniRomDev - [email protected] /data/develop/android/test ] $ CUR_SLOT=$( adb shell getprop ro.boot.slot_suffix )
[ OmniRomDev - [email protected] /data/develop/android/test ] $ echo ${CUR_SLOT}
_b
[ OmniRomDev - [email protected] /data/develop/android/test ] $
[ OmniRomDev - [email protected] /data/develop/android/test ] $ adb shell su - -c dd if=/dev/block/by-name/boot${CUR_SLOT} | cat >boot${CUR_SLOT}.img
196608+0 records in
196608+0 records out
100663296 bytes (96 M) copied, 2.668147 s, 36 M/s
[ OmniRomDev - [email protected] /data/develop/android/test ]
[ OmniRomDev - [email protected] /data/develop/android/test ] $ ls -ltr boot${CUR_SLOT}.img
-rw-r--r--. 1 xtrnaw7 xtrnaw7 100663296 Oct 1 12:13 boot_b.img
[ OmniRomDev - [email protected] /data/develop/android/test ] $
To trouble shoot issues with this approach it is highly recommended to create an Magisk init script in the directory
/data/adb/post-fs-data.d
to fetch and store the Android logs into a persistent file. Use these commands to create the script:
Code:
cat >/data/adb/post-fs-data.d/0002logcatboot <<-EOT
mkdir -p /cache/logs
# backup the OS logs from before the reboot:
#
[ -r /cache/logs/log ] && mv /cache/logs/log /cache/logs/oldlog
/system/bin/logcat -r 102400 -n 9 -v threadTime -f /cache/logs/log >/cache/logs/info.log 2>/cache/logs/err.log &
EOT
chmod 755 /data/adb/post-fs-data.d/0001logcatboot
Using this script the log messages from before the last reboot are stored in the file /cache/logs/oldlog.
To activate the script the phone must be rebooted.
Check the contents of the directory /cache/logs/log after the reboot as user root to be sure that it works.
Code:
[email protected]_I006D:/ $ su - -c ls -ltr /cache/logs
total 205008
-rw-rw-rw- 1 root root 0 1970-01-06 08:16 info.log
-rw-rw-rw- 1 root root 0 1970-01-06 08:16 err.log
-rw-r----- 1 root root 4707523 2022-10-01 17:29 log
[email protected]_I006D:/ $
Details
The trigger in the .rc files for the action that should be done while shutting down is
on shutdown
The trigger can be used more then once; the OS will execute all defined actions for the trigger in the order they are found in the rc files.
The action to run an executable in the .rc file is
exec [ <seclabel> [ <user> [ <group>\* ] ] ] -- <command> [ <argument>\* ]
Fork and execute command with the given arguments. The command starts after “--” so that an optional security context, user, and supplementary groups can be provided. No other commands will be run until this one finishes. seclabel can be a - to denote default. Properties are expanded within argument. Init halts executing commands until the forked process exits.
Click to expand...
Click to collapse
In Android SELinux is enabled by default. Therefor it's neccessary to use the correct SELinux context for the files used.
(Note: The SELinux context for the init process executing the action is u:r:init:0 )
It's quite difficult to find the correct SELinux contexts in Android for this approach therefor it's better to use the general SELinux context defined by Magisk: u:r:magisk:s0 .
Implementation
Note:
All commands must be done as user root in an session on the phone or in an adb session.
So first create the neccessary directories and files:
Code:
mkdir -p /data/init_scripts
mkdir -p /data/init_scripts/log
Create the script to execute on shutdown:
Code:
cat >/data/init_scripts/my_shutdown.sh <<-\EOT
#!/system/bin/sh
SHUTDOWN_LOG="/data/init_scripts/log/myshutdown.$$.log"
echo "$0: Shutdown with parameter \"$*\" started at $( date ) " >>${SHUTDOWN_LOG}
echo "*** id : " >>${SHUTDOWN_LOG} 2>&1
id >>${SHUTDOWN_LOG} 2>&1
# ... add necessary commands ...
EOT
chmod 755 /data/init_scripts/my_shutdown.sh
Correct the SELinux context:
Code:
chcon -R u:r:magisk:s0 /data/init_scripts/
Check the result
Code:
[email protected]_I006D:/ # find /data/init_scripts/ -exec ls -ld {} \;
drwxr-xr-x 3 root root u:r:magisk:s0 3452 2022-10-01 16:12 /data/init_scripts/
-rwxr-xr-x 1 root root u:r:magisk:s0 637 2022-10-01 16:12 /data/init_scripts/my_shutdown.sh
drwxr-xr-x 2 root root u:r:magisk:s0 3452 2022-10-01 16:16 /data/init_scripts/log
[email protected]_I006D:/ #
Create a working directory:
Code:
#
# create a working directory
#
mkdir -p /data/adb/workdir
cd /data/adb/workdir
Now create the additional .rc file:
Code:
#
# change the current directory to the working directory
#
cd /data/adb/workdir
cat >init.custom.rc <<-\EOT
on shutdown
exec u:r:magisk:s0 -- /system/bin/sh /data/init_scripts/my_shutdown.sh 0008
on early-init
setprop my_custom_rc_file loaded
EOT
Note:
The additional trigger for early-init is for testing the new .rc file (see the trouble shooting section below for details). Magisk supports more then one .rc file; the name of the .rc file is meaningless but the extension must be .rc.
And now add the new file to the ramdisk on the boot partition:
Code:
#
# change the current directory to the working directory
#
cd /data/adb/workdir
# get the current active slot
#
CURRENT_SLOT=$( getprop ro.boot.slot_suffix )
echo "The current active slot is: ${CURRENT_SLOT}"
# copy the boot partition from the active slot to a file
#
dd if=/dev/block/by-name/boot${CURRENT_SLOT} of=./boot_root.img
# unpack the image file
#
/data/adb/magisk/magiskboot unpack ./boot_root.img
# add the new dirs and files to the ramdisk from the boot partition
#
/data/adb/magisk/magiskboot cpio ramdisk.cpio \
"mkdir 0700 overlay.d" \
"add 0700 overlay.d/init.custom.rc init.custom.rc"
# recreate the image file for the boot partition
#
/data/adb/magisk/magiskboot repack boot_root.img
# write the corrected image file to the boot partition
#
dd if=./new-boot.img of=/dev/block/by-name/boot${CURRENT_SLOT}
Note:
The commands to unpack and pack the ramdisk manually using the cpio command are (if NOT using the Magisk binary magiskboot):
Code:
RAMDISK=$PWD/ramdisk
mkdir ${RAMDISK}
cd ${RAMDISK}
# unpack the ramdisk
#
cpio -idm <../ramdisk.cpio
# ... do what ever is necessary with the files/dirs in ${RAMDISK}
# pack the ramdisk again
#
cd ${RAMDISK}
find . | cpio -o >../ramdisk.cpio
Now reboot the phone to activate the new .rc config and after the reboot check that the .rc file was processed
Code:
getprop my_custom_rc_file
e.g
Code:
[email protected]_I006D:/ $ getprop my_custom_rc_file
loaded
[email protected]_I006D:/ $
If the property defined in the .rc file, my_custom_rc_file, is not set something went wrong and you should check the OS logs and double check your config.
If the new property is defined you can test the shutdown action by rebooting the phone again.
While doing this reboot the new shutdown script should be executed and after the reboot is done there should be the log file from the shutdown script:
Code:
[email protected]_I006D:/ $ su -
[email protected]_I006D:/ # ls -l /data/init_scripts/log
total 0
-rw------- 1 root root 179 2022-10-01 18:23 myshutdown.4617.log
[email protected]_I006D:/ # cat /data/init_scripts/log/myshutdown.4617.log
/data/init_scripts/my_shutdown.sh: Shutdown with parameter "0008" started at Sat Oct 1 18:23:14 CEST 2022
*** id :
uid=0(root) gid=0(root) groups=0(root) context=u:r:magisk:s0
[email protected]_I006D:/ #
That's it.
Note that you can change the script executed while doing the shutdown without changing the boot image again.
But you should always test the script before rebooting -- an error in your script may stop the reboot.
To change the additional .rc files it's necessary to recreate the ramdisk and boot partition.
The filesystems for /data and for /sdcard are still mounted while executing the actions for the trigger "on shutdown" .
To log the current environment while executing the shutdown script you can add code like this to the script:
Code:
(
echo
echo "*** Environment while executing the shutdown script ..."
echo
echo "*** pwd: "
pwd
echo
echo "*** id: "
id
echo
echo "*** df -h: "
df -h
echo
echo "*** ps -efZ : "
ps -efZ
echo
echo "*** env: "
env
echo
echo "*** set: "
set
echo
) >>/data/init_scripts/log/myshutdown_env.log 2>&1
To create a directory in which other actions from the .rc file (like write) can write with SELinux enabled use one of the SELInux contexts the init process can write to, e.g:
Code:
mkdir /data/system_data
chcon u:object_r:system_data_file:s0 /data/system_data
Now the .rc config
Code:
on shutdown
write /data/system_data/myshutdown.log Shutdown_started\n
will work.
See the file ./plat_file_contexts in the ramdisk from the boot partition for other existing SELinux contexts, e.g.:
Code:
[email protected]_I006D:/data/adb/test # /data/adb/magisk/magiskboot cpio ramdisk.cpio "extract plat_file_contexts plat_file_contexts" <
Loading cpio: [ramdisk.cpio]
Extract [plat_file_contexts] to [plat_file_contexts]
[email protected]_I006D:/data/adb/test # ls -l plat_file_contexts
-rw-r--r-- 1 root root 40490 2022-10-03 16:27 plat_file_contexts
[email protected]_I006D:/data/adb/test #
Please be aware that these changes will be gone after the next OS update. But on the other hand it's quite easy to create a script to re-install the shutdown script without user intervention.
Trouble Shooting
The main reason for problems with this approach are invalid SELinux contexts. Therefor you should test your script in permissive SELinux mode if it does not work like expected. To do that temporary disable SELinux before rebooting (SELinux will be automatically enabled again after the reboot), e.g.:
Code:
# set SELinux to permissive
#
setenforce 0
reboot
and check the log messages in the directory /cache/logs/oldlog for SELinux related messages:
Code:
su - -c grep deny /cache/logs/oldlog
Note that you can not disable SELinux in an action in an .rc file.
To check if your additional .rc file is processed by Magisk add a statement like these to the custom .rc file in the overlay directory:
Code:
on early-init
setprop sys.example.foo bar
If this statement is processed by Magisk and Android the property sys.example.foo should be defined after the reboot, e.g.:
Code:
[email protected]_I006D:/ # getprop sys.example.foo
bar
[email protected]_I006D:/ #
To check if the "on shutdown" trigger is processed use :
Code:
on shutdown
write /sdcard/Download/myshutdown.log Shutdown_started\n
and reboot with disabled SELinux:
Code:
setenforce 0
reboot
If the "on shutdown" trigger in your .rc file is processed there should exist the file
/sdcard/Download/myshutdown.log
after the reboot
If the shutdown of the phone hangs open another adb session to the phone and kill the script (the adb daemon should still run while the shutdown script is running).
If the phone does not boot anymore with the new shutdown script reboot the phone from the TWRP image and fix / delete the new shutdown script. Or reflash the boot partition with the image file created before starting the development.
In general you should carefully check your .rc file for syntax errors -- entries in the file after the first syntax error will be ignored
Useful URLs
I used ideas and code from the web pages listed below for this HowTo:
How to run an executable on boot and keep it running?
How to run an Android init service with superuser SELinux context?
Magisk overlay - execute a script or copy files
History
03.10.2022 /bs
added code about to extract a single file (plat_file_contexts) from the ramdisk cpio image using magiskboot
How to trigger an action when a property is changed
In Android it's possible to trigger various actions by changing the value of a property.
This feature is quite handy and the implementation using Magisk is not really difficult.
As an example:
In the original Android from ASUS for the Zenfone 8 you can disable and enable the swap on a ZRAM device by changing the value for the property vendor.zram.enable:
e.g.:
To turn the swap on use
Code:
setprop vendor.zram.enable 1
and to turn the swap off use
Code:
setprop vendor.zram.enable 0
To get the current value use
Code:
getprop vendor.zram.enable
or
check the output of the OS command free.
(see How to disable or change the swap device in the Android 12 from ASUS for the Zenfone 8 for details)
This feature is not implemented in the OmniROM for the ASUS Zenfone 8 but quite useful so let's see how to implement it in the OmniROM.
The Triggers and Action for this Android feature are configured in the init.rc files in the root filesystem for the OS (see https://android.googlesource.com/platform/system/core/+/master/init/README.md for details). The root filesystem for Android is read-only mounted so without creating your own Android OS image for the phone it's not possible to add the functionality to the OS.
But we can use the Root Directory Overlay System from Magisk (see https://github.com/topjohnwu/Magisk/blob/master/docs/guides.md for the documentation) to implement it.
The detailed process for creating additional *.rc files for Android via Magisk is described here:
How to run a script at shutdown
Therefore I will not go into the details here. But please read that post before you continue
First we check how this feature is implemented in the Original Android for the Zenfone:
Enabling and disabling the swap device on ZRAM is configured in the .rc file
/vendor/etc/hw/init.asus.debugtool.rc
using these settings in the original Android OS for the Zenfone 8:
Code:
service asus_zram /system/vendor/bin/sh /vendor/bin/init.asus.zram.sh
user root
group root
disabled
seclabel u:r:vendor_qti_init_shell:s0
oneshot
on property:persist.vendor.zram.enable=1
setprop vendor.zram.enable "1"
setprop vendor.zram.disksize ${persist.vendor.zram.disksize}
on property:persist.vendor.zram.enable=0
setprop vendor.zram.enable "0"
setprop vendor.zram.disksize ${persist.vendor.zram.disksize}
on property:vendor.zram.enable=*
start asus_zram
The script used to enable or disable the swap device on ZRAM in the original Android for the Zenfone 8 is:
/vendor/bin/init.asus.zram.sh
The script is quite simple (see also below):
It uses two properties to configure the swap device:
vendor.zram.enable : if this property is set to 1 the script enables the swap device and if the property is set to 0 it disables the swap device
vendor.zram.disksize : the value of this property is the size of the ramdisk.
Now we can implement this feature for the OmniROM:
Note:
All commands must be done as user root in a shell on the phone or in an adb shell
First we check the prerequisites for the feature:
The used shell for the service exists in the OmniROM:
Code:
[email protected]_I006D:/data/adb/workdir # ls -Zl /vendor/bin/sh
-rwxr-xr-x 1 root shell u:object_r:vendor_shell_exec:s0 318216 2009-01-01 01:00 /vendor/bin/sh
[email protected]_I006D:/data/adb/workdir #
The script to toggle the ramdisk on the swap device also already exists in the OmniROM:
Code:
[email protected]_I006D:/data/adb/test # ls -l /vendor/bin/init.asus.zram.sh
-rwxr-xr-x 1 root shell 1127 2009-01-01 01:00 /vendor/bin/init.asus.zram.sh
[email protected]_I006D:/data/adb/test #
And the necessary SELinux contexts are also already defined in the OmniROM.
So, let's start:
Code:
# create a temporary directory
#
mkdir /data/adb/workdir
cd /data/adb/workdir
# create the additional .rc file
#
cat >init.asus.zram.rc <<-\EOT
#
# Note:
#
# The service definition for an OS without the script init.asus.zram.sh should be
#
# service asus_zram /system/bin/sh /system/sbin/init.asus.zram.sh
#
service asus_zram /system/vendor/bin/sh /vendor/bin/init.asus.zram.sh
user root
group root
disabled
seclabel u:r:vendor_qti_init_shell:s0
oneshot
#
# these properties can be used to define the initial state of the ramdisk on ZRAM
#
on property:persist.vendor.zram.enable=1
setprop vendor.zram.enable "1"
setprop vendor.zram.disksize ${persist.vendor.zram.disksize}
on property:persist.vendor.zram.enable=0
setprop vendor.zram.enable "0"
setprop vendor.zram.disksize ${persist.vendor.zram.disksize}
on property:vendor.zram.enable=*
start asus_zram
# The property persist.vendor.zram.enable is not defined in the OmniROM. If necessary you can add another triger in the .rc file,
# e.g to enable the swap device by default use
#
on early-init
setprop persist.vendor.zram.enable 1
EOT
# get the current active slot
#
CURRENT_SLOT=$( getprop ro.boot.slot_suffix )
echo "The current active slot is: ${CURRENT_SLOT}"
# copy the boot partition from the active slot to a file
dd if=/dev/block/by-name/boot${CURRENT_SLOT} of=./boot_root.img
# unpack the image file
/data/adb/magisk/magiskboot unpack ./boot_root.img
# add the new dir and file to the ramdisk from the boot partition
/data/adb/magisk/magiskboot cpio ramdisk.cpio \
"mkdir 0700 overlay.d" \
"add 0700 overlay.d/init.custom.rc init.asus.zram.rc"
# recreate the image file for the boot partition
/data/adb/magisk/magiskboot repack boot_root.img
# write the corrected image file to the boot partition
dd if=./new-boot.img of=/dev/block/by-name/boot${CURRENT_SLOT}
That's it.
After the next reboot switching the ramdisk on the ZRAM device via an property should be active:
Code:
[email protected]_I006D:/ # reboot
# .....
# start a new adb session
# ....
[email protected]_I006D:/ $ getprop ro.omni.version
12-20220703-zenfone8-MICROG
#
# Note: The property is only visible to the user root
#
[email protected]_I006D:/ $ su -
[email protected]_I006D:/ # id
uid=0(root) gid=0(root) groups=0(root) context=u:r:magisk:s0
[email protected]_I006D:/ #
[email protected]_I006D:/ # free
total used free shared buffers
Mem: 7612493824 4835229696 2777264128 14585856 14487552
-/+ buffers/cache: 4820742144 2791751680
Swap: 4294963200 0 4294963200
[email protected]_I006D:/ #
[email protected]_I006D:/ # getprop vendor.zram.enable
1
[email protected]_I006D:/ #
# -> now disable the swap on ZRAM
[email protected]_I006D:/ # setprop vendor.zram.enable 0
[email protected]_I006D:/ #
[email protected]_I006D:/ # getprop vendor.zram.enable
0
[email protected]_I006D:/ #
[email protected]_I006D:/ # free
total used free shared buffers
Mem: 7612493824 4840824832 2771668992 14524416 14483456
-/+ buffers/cache: 4826341376 2786152448
Swap: 0 0 0
[email protected]_I006D:/ #
# -> now enable the swap on ZRAM again
[email protected]_I006D:/ # setprop vendor.zram.enable 1
[email protected]_I006D:/ #
[email protected]_I006D:/ # getprop vendor.zram.enable
1
[email protected]_I006D:/ #
[email protected]_I006D:/ # free
total used free shared buffers
Mem: 7612493824 4844777472 2767716352 14524416 14512128
-/+ buffers/cache: 4830265344 2782228480
Swap: 4294963200 0 4294963200
[email protected]_I006D:/ #
Workarounds for other configuration
Find below some workarounds for OS versions without the prerequisites for implementing this feature.
1. The script to toggle the swap /vendor/bin/init.asus.zram.sh does not exist
If the script /vendor/bin/init.asus.zram.sh does not exist in your OS create a Magisk Module for the script
To create a (dummy) Magisk Module for the script do:
Code:
mkdir -p /data/adb/modules/toggle_ram/system/bin
#
# create the script to toggle the ramdisk on ZRAM
#
cat >/data/adb/modules/toggle_ram/system/bin/init.asus.zram.sh <<-\EOT
lahaina_set=`getprop vendor.asus.zram_setting`
if test "$lahaina_set" != "1"; then
echo "[asus_zram] init.kernel.post_boot-lahaina.sh not finished yet!"> /dev/kmsg
exit 0
fi
disksize=`getprop vendor.zram.disksize`
zram_enable=`getprop vendor.zram.enable`
MemTotalStr=`cat /proc/meminfo | grep MemTotal`
MemTotal=${MemTotalStr:16:8}
let RamSizeGB="( $MemTotal / 1048576 ) + 1"
if test "$disksize" = ""; then
disksize="4096M"
fi
echo "[asus_zram]RamSizeGB=${RamSizeGB}" > /dev/kmsg
if test "$zram_enable" = "1"; then
if [ $RamSizeGB -le 7 ]; then #this is for 6G; or the value will be 4G(8G,12G,16G,18G,etc)
disksize="( $RamSizeGB * 1024 ) / 2""M"
fi
swapoff /dev/block/zram0 2>/dev/kmsg
echo 1 > sys/block/zram0/reset 2>/dev/kmsg
sleep 1
echo lz4 > /sys/block/zram0/comp_algorithm
echo $disksize > /sys/block/zram0/disksize 2>/dev/kmsg
mkswap /dev/block/zram0 2>/dev/kmsg
swapon /dev/block/zram0 -p 32758 2>/dev/kmsg
echo "[asus_zram]write zram disksize=${disksize}" > /dev/kmsg
fi
if test "$zram_enable" = "0"; then
swapoff /dev/block/zram0 2>/dev/kmsg
echo "[asus_zram]turn off the zram" > /dev/kmsg
fi
EOT
chmod 755 /data/adb/modules/toggle_ram/system/bin/init.asus.zram.sh
chown root:shell /data/adb/modules/toggle_ram/system/bin/init.asus.zram.sh
chcon u:object_r:vendor_file:s0 /data/adb/modules/toggle_ram/system/bin/init.asus.zram.sh
Check the result:
Code:
[email protected]_I006D:/ # ls -lZ /data/adb/modules/toggle_ram/system/bin/init.asus.zram.sh
-rwxr-xr-x 1 root shell u:object_r:vendor_file:s0 1109 2022-10-03 21:14 /data/adb/modules/toggle_ram/system/bin/init.asus.zram.sh
[email protected]_I006D:/ #
Then change the script to execute in the service definition in the .rc file to /system/bin/init.asus.zram.sh:
Code:
service asus_zram /system/vendor/bin/sh /system/bin/init.asus.zram.sh
The rest of the instructions can be be used without changes.
2. The binary /system/vendor/bin/sh does not exist
If the shell /system/vendor/bin/sh does not exist in the OS create an Magisk Module with an approbiate shell:
Note:
The shell /system/bin/sh can not be used because it's configured with another SELinux context:
Code:
[email protected]_I006D:/ # ls -lZ /system/vendor/bin/sh
-rwxr-xr-x 1 root shell u:object_r:vendor_shell_exec:s0 318216 2009-01-01 01:00 /system/vendor/bin/sh
[email protected]_I006D:/ #
# but
[email protected]_I006D:/data/adb/workdir # ls -Zl /system/bin/sh
-rwxr-xr-x 1 root shell u:object_r:shell_exec:s0 307768 2009-01-01 01:00 /system/bin/sh
[email protected]_I006D:/data/adb/workdir #
To create a (dummy) Magisk Module for the necessary shell do:
Code:
mkdir -p /data/adb/modules/vendorshell/system/bin
cp /system/bin/sh /data/adb/modules/vendorshell/system/bin/sh
chcon u:object_r:vendor_shell_exec:s0 /data/adb/modules/vendorshell/system/bin/vendor_sh
Check the result:
Code:
[email protected]_I006D:/data/adb/workdir # ls -lZ /data/adb/modules/vendorshell/system/bin/vendor_sh
-rwxr-xr-x 1 root root u:object_r:vendor_shell_exec:s0 307768 2022-10-03 20:41 /data/adb/modules/vendorshell/system/bin/vendor_sh
[email protected]_I006D:/data/adb/workdir #
Now change the shell in the service definition in the .rc file to /system/bin/vendor_sh:
Code:
service asus_zram /system/bin/vendor_sh /vendor/bin/init.asus.zram.sh
The rest of the instructions can be be used without changes.
3. The necessary shell /system/vendor/bin/sh and the script /vendor/bin/init.asus.zram.sh do both not exist
If the necessary shell /system/vendor/bin/sh and the script /vendor/bin/init.asus.zram.sh do not exist you can also create one (dummy) Magisk module for both.
See
https://topjohnwu.github.io/Magisk/guides.html
and
Some hints for using Magisk on Android phones
for instructions and infos about how to create a real Magisk Module
4. Missing SELinux contexts
These instructions assume that all necessary SELinux contexts are already defined in the used OS.
If there are SELinux contexts missing it might not work without adding the missing SELinux contexts
(that might be difficult and I must admit that I did not test that)
5. only for the records:
The magiskboot command can also be used to add new files to the /sbin directory in the root filesystem.
This can be can be configured like this:
Code:
/data/adb/magisk/magiskboot cpio ramdisk.cpio \
"mkdir 0700 overlay.d" \
"add 0700 overlay.d/init.custom.rc init.asus.zram.rc" \
"mkdir 0700 overlay.d/sbin" \
"add 0700 overlay.d/sbin/my_new_script.sh my_script.sh"
This is useful for adding binaries or scripts for actions that should be executed while the other partitions are not yet mounted and therefor the files in these filesystems not yet available. But for the action defined in this post this is not necessary.
And be aware that the files added to the root filesystem ( /sbin/my_new_script.sh in this example) is only available while booting the phone.
6. Other problems
In case of problems please check the post
How to run a script at shutdown
again.
Also check the restrictions for this approach documented in that post
History
06.10.2022 /bs
corrected some typos