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Nikos Grigoriadis
Asked: 2014-05-21 03:02:09 +0800 CST

How to edit a protected file if I have no direct access to the filesystem?

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I changed the brightness of my machine by editing the /etc/rc.local file and adding this line echo 10 > /sys/class/backlight/nv_backlight/brightness before exit 0.

After reboot I can see that it works fine. The problem is, it's so dark that I can't see anything. The screen is completely black. I tried running a live USB to edit the file but I have no write permissions.

Any ideas on how to resolve this?

14.04

1 Answers

  1. Best Answer

    You have a bountiful bevy of options, I'll start with the easiest and work through:

    • Do you have backlight control keys on your keyboard? Many laptops do and they might work here long enough to let you edit that file.

    • If you have previously installed a SSH server, you could SSH in from another computer and sudo nano /etc/rc.local. The same goes for other remote solutions NX/VNC/RDP will all let you get into a position where you're sitting with a terminal in front of you.

    • Boot into Recovery Mode. Apparently this won't load rc.local. You'll need to run mount -o remount,rw / first but then you should be able to run nano /etc/rc.local.

    • LiveUSB/CD: mount the disk somewhere and (from the command line) sudo nano /media/.../etc/rc.local — just remember to edit the mounted version, not the Live version.

    • Jedi it. Boot up normally, Control+Alt+F1. Type your username followed by Return. Then your password and Return... And then carefully type in sudo sed -i '/backlight/d' /etc/rc.local followed by Return. Then type your password (for sudo) followed by Return. sudo reboot Return to safely reboot.

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