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When I update my Ubuntu, appear

W:Failed to fetch  Unable to find expected entry 'non-free/source/Sources' in Release file (Wrong sources.list entry or malformed file)
E:Some index files failed to download. They have been ignored, or old ones used instead.

What can I do for fix this error on my Virtual Box?

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what version of ubuntu are you on? – Goddard Oct 9 '13 at 16:28
In addition to Goddard's question, what version of VirtualBox? And had you installed Guest Additions in the Ubuntu environment? – Colyn1337 Oct 9 '13 at 17:11
My version is 4.2.18 and I don't know if Guest Additions is installed in my Ubuntu. How can I install? – Vitor Mazuco Oct 9 '13 at 17:54
My Ubuntu is 12 version – Vitor Mazuco Oct 9 '13 at 17:56
up vote 2 down vote accepted

Looks like you are using the wrong distribution codename in the sources.list file.

I personally prefer to have a separate file for each 3rd party repository, you can create one for virtualbox using the following in CLI:

sudo echo "deb `lsb_release -sc` contrib" > /etc/apt/sources.list.d/virtualbox.list

After creating virtualbox.list, remove or comment out the out-dated line from your sources.list.

It may look like this => deb lucid contrib non-free.

Once done, update your system sudo apt-get update && apt-get dist-upgrade -y.

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The reason is an invalid entry in /etc/apt/sources.list file. There is no source package in the VirtualBox source repository. Just remove the deb-src line:

sudo nano /etc/apt/sources.list

Remove or comment this line:

deb-src lucid non-free

This should solve the case.

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