Where are KERN_DEBUG log levels written to in Android? If I were, for example, to call
printk(KERN_DEBUG "666 The beast lives here 666");
then where is the output written?
I figured it out. In Android, output of printk can be read with
$ adb shell cat /proc/kmsg
or, provided a prior log was written to before, then with
$ adb shell /proc/last_kmsg
or with
$ adb shell dmesg
Related
Dead simple question. My program runs for 12s, and then prints to stdout. When starting it with adb shell command, it does not even start...
$ adb shell
# /data/myprogram
CPU time: 12682.4 ms
$ adb shell /data/myprogram
<nothing>
$
My program runs for 12s, the log is a std::cout C++ print in stdout. I use adb-v1.0.32. My dev board runs android-5.0.2, with root access. When trying to execute it with adb shell, it returns to the prompt quickly. I checked if the program ran in background with busybox ps, it does not.
What am i missing?
I am trying to do a logcat to a file using adb shell by following command -
adb shell "nohup logcat -f /storage/sdcard0/myLog.txt -v time &"
If I do a ps | grep logcat, I don't see the logcat command. Even I tried to see nohup command, but it is not there. So somehow above command does not work.
However if I perform the command in 2 steps it works fine -
adb shell
nohup logcat -f /storage/sdcard0/myLog.txt -v time &
I can see the process using ps and logcat continues to record to the file even if I disconnect adb shell. Now I would like the first command to work, since I am using python scripts to issue commands via ADB. It is possible to change the python scripts, however I would like to know if I am doing anything wrong in issuing the first command and if it is possible to make it work.
try
adb logcat
not
adb shell logcat
Is there a way to write a script that will copy files from an ADB shell using run-as?
The only way I know of to copy in the adb shell is using cat source > dest (edit: modern android versions have the cp command, which makes this question unnecessary), but I am only able to quote the greater-than sign one level deep - so my script can pass it to adb shell, but not to adb shell run-as.
For example, this works:
adb shell "cat source > dest"
But this does not:
adb shell run-as "cat source > dest"
Nor this:
adb shell "run-as cat source \> dest"
I even tried created a small script and uploading it to the device, but I can't seem to run the script from the adb shell - it tells me "permission denied". I can't chmod the script, either.
The reason I want to do this is to copy a file into an app's private storage area - specifically, I am using a script to modify shared preferences and put the modified preferences back. Only the app itself or root can write to the file I want, however.
The use case in this scenario is coping a file to a protected location on the device, not retrieving it; for retrieving, there are already good answers in this question.
The OP tried to combine the following 3 commands (that he had no problem executing one after another in the interactive shell session) into a single non-interactive command:
adb shell
run-as com.example.app
cat /sdcard/temp_prefs.xml > shared_prefs/com.example.app_preferences.xml
For simplicity let's start from within an interactive adb shell session. If we just try to combine the last two commands into a single line:
run-as com.example.app cat /sdcard/temp_prefs.xml > shared_prefs/com.example.app_preferences.xml
This would not work because of how shell redirection works - only the cat /sdcard/temp_prefs.xml part of the command would be run with com.example.app UID
Many people "know" to put the part of the command around redirection into quotes:
run-as com.example.app "cat /sdcard/temp_prefs.xml > shared_prefs/com.example.app_preferences.xml"
This does not work because the run-as command is not smart enough to parse the whole command. It expects an executable as the next parameter. The proper way to do it would be to use sh instead:
run-as com.example.app sh -c "cat /sdcard/temp_prefs.xml > shared_prefs/com.example.app_preferences.xml"
So can we just prepend adb shell to the command and be done with it? Not necessarily. By running the command from your PC you also add another local shell and its parser. Specific escape requirements would depend on your OS. In Linux or OSX (if your command does not already contain any ') it is easy to single-quote the whole command like so:
adb shell 'run-as com.example.app sh -c "cat /sdcard/temp_prefs.xml > shared_prefs/com.example.app_preferences.xml"'
But sometimes it is just easier to use an alternative solutions with (-out or less) quotes:
adb shell run-as com.example.app cp /sdcard/temp_prefs.xml shared_prefs/com.example.app_preferences.xml
Or if your device does not have the cp command:
adb shell run-as com.example.app dd if=/sdcard/temp_prefs.xml of=shared_prefs/com.example.app_preferences.xml
Also notice how I used shared_prefs/com.example.app_preferences.xml instead of full /data/data/com.example.app/shared_prefs/com.example.app_preferences.xml - normally inside of run-as command your current directory is the HOME dir of your package.
Following Chris Stratton's advice, the way I eventually got this to work was as follows (for copying shared preferences back to the device):
adb push shared_prefs.xml /sdcard/temp_prefs.xml
cat <<EOF | adb shell
run-as com.example.app
cat /sdcard/temp_prefs.xml > /data/data/com.example.app/shared_prefs/com.example.app_preferences.xml
exit
exit
EOF
Piping directly to adb shell run-as did not work, and I do not know why, but piping to adb shell does. The trick is to then call run-as from the interactive shell, and it continues to accept input from the pipe.
The HERE doc lets me easily embed the newlines to separate commands and in general just makes it readable; I did not have much luck with semicolons, but that might have been because of the way I was doing things. I believe it might work with other methods of piping multiple commands/newlines; I stopped the experiment once I finally got it to work.
The two exits are necessary to prevent a hanging shell (killable with CTRL-C); one for run-as, and the other for adb shell itself. Adb's shell doesn't respond to end-of-file very nicely, it seems.
you could just change the permission of the directory and then pull all the files out. but for me i was looking for just one shared preference file and i was able to get the data like this:
PACKAGE='com.mypackage.cool'
SHAREDPREF_FILE="${PACKAGE}_preferences.xml"
adb shell "run-as $PACKAGE cat /data/data/$PACKAGE/shared_prefs/$SHAREDPREF_FILE">$SHAREDPREF_FILE
now we have the data of the sharedpreference file stored in a file of the same name.
Using the latest adb (ADB v1.0.41 / Version 33.0.3) and a Play Store emulator image I experienced adb root not being granted. I also could not copy from /data/local/ or /storage/emulated/0/ due to not having permissions when run-as com.myapp.app
new_prefs_path="my_machine.xml"
config="$(cat $new_prefs_path)"
my_app_uri="com.myapp.app"
adb shell "run-as $my_app_uri sh -c 'echo \"$config\" > shared_prefs/on_android.xml'"
This fixes it for me as a bash script. It's made slightly more complicated by needing to be configurable for different apps and complex payloads.
We take a file (could be generated earlier in this script) and read it to a variable.
We then start shell, do run-as my app and run echo expanding the read file to a file in shared_prefs.
I've been searching for the last week trying to find an answer to this question.
How do I start an Android app with valgrind? I know I can start an app with the 'am' command, but it starts the app and exits.
I'm writing an app that uses the NDK for native C code, and I need to check it for suspected memory errors.
Edit:
I've learned a little more. You can "wrap" an app with a shell script.
Here's the shell script I'm using:
#!/system/bin/sh
VGPARAMS='--error-limit=no'
export TMPDIR=/data/data/com.starlon.froyvisuals
exec /data/local/Inst/bin/valgrind $VGPARAMS $*
And here's setprop:
adb shell setprop wrap.com.starlon.froyvisuals "logwrapper valgrind"
And here's how I start the app:
adb shell am start -n com.starlon.froyvisuals/.FroyVisuals
I don't think this is right, because I'm not sure where the shell script fits in and I'm not seeing anything in logcat. Any hints?
Edit2:
Oh the shell script is indicated with "setprop" command above. So
adb shell setprop wrap.com.starlon.froyvisuals "logwrapper /data/local/val.sh"
I'm still not seeing anything in logcat.
You can try to clear the logcat first
prompt# adb logcat -c
prompt# adb logcat
You should be able to see the logs coming in once you triggered your application.
am start -a android.intent.action.MAIN -n com.example.hellojni/.HelloJni
I had problems with my shell script and i used this instead.
adb shell setprop wrap.com.example.hellojni "logwrapper /data/local/Inst/bin/valgrind"
You should be able to pass in the parameter right after valgrind
I encountered this problem too. In my situation, I edit the "val.sh" in windows & adb push it to the emulator, but the shell script could not be executed correctly. Then I use a echo "*" > val.sh style to make the "val.sh" and It works well.
So you should first make sure the "val.sh" could be interpreted correctly.
When I execute the command
adb logcat
while running the android emulator, all of the old logs blow past and so I figure they are stored in a file somewhere. Is there a command I can run to clear the logs and start fresh? If not, is there some other way to do this?
Have you tried this?
adb logcat -c
https://developer.android.com/studio/command-line/logcat.html
adb logcat -c
didn't do it for me
adb logcat -b all -c
worked
Dup of
How to empty (clear) the logcat buffer in Android
The following command will clear only non-rooted buffers (main, system ..etc).
adb logcat -c
If you want to clear all the buffers (like radio, kernel..etc), Please use the following commands
adb logcat -b all -c
or
adb root
adb shell logcat -b all -c
For me, adb logcat -c was not working and was giving following error :
failed to clear the 'main' log
For this, I first did :
adb shell
Than I did :
logcat -c
then exit the shell.
This way I was able to clear logcat when same was not getting cleared from adb logcat -c