I'm currently rooted on a Samsung S3 i9300 running a custom rom on Kitkat 4.4.2

I use es file explorer to perform root tasks on directories and files, I wanted to permanently turn off the led lights on my phone's hardware softkeys as I don't use them anymore.

I read somewhere on xda developers that changing the numeric string 255 in the max_brightness file to 0 in /sys/class/leds/mmc1:: and /sys/class/leds/mmc2:: should do the trick.

I have "root explorer" on in Es file explorer and have the right permissions to copy the file over to my SD card but I kept getting a task failed error in the app.

I then decided to go hardcore by using the terminal emulator app from the play store using the Linux command line syntax.

I was able to copy the file over to my SD card but something strange happened, the original file according to es file explorer was 4kb in size while the file copied to the SD card was 2 bytes in size..

I'm really puzzled, is there a better way to copy files from the root directories?

PS: The "mmc1::" and "mmc2::" folder icon has an arrow shortcut icon next to it and I've always been able to copy other files from root directories using es file explorer until this particular file.

1 Answer 1


Files in /sys/ are part of sysfs which is a special virtual filesystem to dialog with the Linux kernel.

You can for example have a fast introduction here.

Therefore you cannot treat sysfs files as normal files as it may lead to strange behaviour depending on how the program treats them (same for device files, usually in /dev, or files in procfs in /proc).

Usually to tweak that files you just write in them with an echo, such as

echo 255 > /sys/class/leds/mmc1::/max_brightness
  • Oh wow.. Thank you so much.. So if I wanted to change 255 to 0 .. I would have to echo in 0 instead of 255 right?
    – Feyisayo
    Commented Jul 22, 2014 at 13:41
  • yep just "echo 0 > /sys/class/.....". be aware that this setting will get back to original value after a reboot. if you want to make it permanent you should put the echo in some boot script. to read the value just use "cat /sys/class/......"
    – fede.evol
    Commented Jul 22, 2014 at 13:45
  • Oh. And do you have a resource where I can learn how to create a boot script?
    – Feyisayo
    Commented Jul 22, 2014 at 13:49

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