How can I modify a file that is owned by root?

Solution 1:

Assuming you are the owner of the operating system in question then you can do something relatively simple. Also assuming the current file is owned by root and group of root then in a terminal you can:

sudo chown your_user:root /path/to/file

You may now edit this file using your normal GUI login.

Once you're done, remember to set it back

sudo chown root:root /path/to/file

To find out more about changing ownership of files see:

man chown

Opening a terminal can be as simple as opening the application bar (name?) and typing "terminal". Using sudo you will be asked for your password to grant you elevated privileges for making the change. See:

man sudo

Solution 2:

Its simple, By default in ubuntu nautilus is the file manager.

So open the file manager with root privileges and change your file

sudo nautilus

Solution 3:

Whenever you need to edit something as root, you can use sudo. Press Ctrl+Alt+T to open a terminal and then write this command and hit enter:

sudo gedit /path/to/file

Obviously, make sure to change /path/to/file with the actual location of your file. This will open a gedit (a simple text editor) window run by root (the administrator) and will allow you to edit your file.

Solution 4:

I'm trying to understand which problem (use case) you actually want to solve.
It looks like you do not actually intend to modify your system files, but to change something in your GUI.
If that's right, see below.

Usually, the best way to make personal changes to files that are part of Ubuntu, is to make a copy of it to your personal files, and modify that. If you can read the file owned by root, you can create a copy, which is owned by you.

Some GUI features even do this automatically in some cases.

As a simple example, if you want to make a change to an existing desktop wallpaper image, you could find the file, copy it, and modify your copy.
Now you can use it as wallpaper image.

(Doing it this way has various advantages, like keeping the original, not creating conflicts when updating the package it belongs to, allowing to do the same for multiple users (and probably more).)