[Q] ADB SHELL CHMOD 644 ,nothing is working anymore... topic

Hello everybody
I needed to push a file to /system/app but since I was on stock rom & kernel, that didnt support adb root.
I needed to be able to push the backup file after restart but ADBD Insecure couldn't patch after restart.
my phone is optimus G E975 , fully stock 4.1.2
I found this command which could do the thing BUT :
adb shell
su
chmod 777 /system

since it didnt restore to default after restarted I tried to restore it myself(didn't work) with:
adb shell
su
chmod 644 /system
but after that every thing force stopped & after restart, phone can't boot anymore,just when want t start boot animation, it just cant & goes to recovery every time!:(
even Hard reset didnt work, but as stock recovery supports adb, I wish you guys can help me. but It seems adb shell gives permission denied(13) in recovery. please someone help...
Anyway am I able to flash in download mode????? (for the last solution)
any help to change that CHMOD to 777 in recovery or something else?
any help appreciated so much!

[Q] Failed chmod? topic

I recently tried to root a friend's phone (a MT6572), using the Root Master Cekas app (it won't let me post outside links, as I recently made this account, but anyone can find a tutorial by searching "root master cekas tutorial" on Google, to see the app used) . It succeeded, and since it installs the Cekas app as a SuperSU, I was going to replace it in /system/app with the Chainfire SuperSU APK file (which I have done before, on an old tablet, and that worked). In a Terminal window, I used the command "chmod 644 /system/app", thinking that was the correct command (last I did it was around a month ago), but right when I did it, all apps started to close. He couldn't do anything, so he tried restarting it, and it freezes whenever he tries to do anything.

So my main question is, is there any way to use ADB/fastboot without having USB debugging active (he can't get into the settings menu) ? Or is there any possible way to turn it on remotely from a PC?


Thank you for your time,
Takumi