How do I restore the default repositories?

There are now errors when updating and I cannot install most software due to a corrupted

/etc/apt/sources.list

file. Is there a copy I can download to replace it?

The file would be for Ubuntu 12.04 (Final Beta) in the United States.

4 Answers

You can use this trick. Open a terminal ( Pressing Ctrl+Alt+T ) and do these

Move the corrupted one to the safe place

sudo mv /etc/apt/sources.list ~/

and recreate it

sudo touch /etc/apt/sources.list

Open Software & Updates
```
software-properties-gtk
```
This will open software-properties-gtk with no repository selected.

Then, change the server to Main server or to any other server of your choice. You must enable some repositories from the new window in order to create a new sources.list file in /etc/apt/.

After enabling some sources from Ubuntu software tab, you can enable updates. To do so, switch to Updates tab and select one or more updates channel. I recommend selecting the security and updates channels at least. (This image is later added from Ubuntu xenial, so there can be some differences)

Updated with inline content

This is the sources.list file for 12.04 Precise Pangolin.

###### Ubuntu Main Repos
deb precise main restricted universe multiverse
deb-src precise main restricted universe multiverse
###### Ubuntu Update Repos
deb precise-security main restricted universe multiverse
deb precise-updates main restricted universe multiverse
deb precise-proposed main restricted universe multiverse
deb precise-backports main restricted universe multiverse
deb-src precise-security main restricted universe multiverse
deb-src precise-updates main restricted universe multiverse
deb-src precise-proposed main restricted universe multiverse
deb-src precise-backports main restricted universe multiverse
###### Ubuntu Partner Repo
deb precise partner
deb-src precise partner
###### Ubuntu Extras Repo
deb precise main
deb-src precise main

If you're using another release, you need to replace the precise word with your Ubuntu release name. You can see which name you should use with this command:

lsb_release -c -s

To replace the word, you can use this sed command (assuming you copied the sources content in /etc/apt/sources.list):

sudo sed -i "s/precise/$(lsb_release -c -s)/" /etc/apt/sources.list

Note 1: the word deb and deb-src refers to the repository format. deb is for binary packages and deb-src is for source packages.

Note 2: Using # at the start of the line makes that line a comment. apt will ignore it, so any repositories mentioned on that line will be disabled.

Note 3: There are repository lines which includes all four components: main, universe, restricted, multiverse. You can disable one or more of them by removing the word.

Note 4: You can find some explanation of the repositories in this my other answer

For releases prior to and including 18.04, you can use (currently, 20.04 and later are not supported by this tool).

Select your Country and Ubuntu Release.

For the default set of repositories, you need to enable these repositories.

All of the Ubuntu Branches repositories.
Security - Important Security Updates.
Security Sources Repository
Updates - Recommended Updates
Updates Sources Repository

If you want to install software from Canonical Partner Repositories (closed source software), enable the Ubuntu Partner Repositories (both of them).

Enable any 3rd party repository you wish to enable.

Now, click the Generate List button at the bottom of that page and you'll see your generated sources.list.

Replace the old sources.list with the new one

Run the following commands in a Terminal.

sudo mv /etc/apt/sources.list /etc/apt/sources.list.old
gksudo gedit /etc/apt/sources.list

Copy/paste all the text from the newly generated sources.list to this file. Save it and close Gedit.

Now, update apt.

sudo apt-get update

This will update your repository index with the current sources.list and then you can install any software using Software Center, Synaptic or apt-get.

By default there will be a backup for your sources.list file on the same directory itself.

sudo cp /etc/apt/sources.list.save /etc/apt/sources.list

Answer from similar question here: What is the correct output of cat /etc/apt/sources.list?

Here is a better way to get all the default repositories back.

Create a directory where we can run our commands:
```
sudo mkdir ~/answer
```
Download the sources.list for Ubuntu 20.04 focal.
```
cd ~/answer/
sudo wget 
```

Change the sources.list to match your version:

sudo sed -i "s/focal/$(lsb_release -c -s)/" ~/answer/sources.list

Backup your current sources.list:

sudo mv /etc/apt/sources.list /etc/apt/sources.list.bak

Replace the sources.list:
```
sudo mv ~/answer/sources.list /etc/apt/
```
Run apt update:
```
sudo apt update
```

By default, the directory which contains all the PPA files is empty. If after restoring the repositories, you're still facing errors then you need to remove all the PPA files too.

Move the directory containing the PPA files to the ~/answer directory:
```
sudo mv /etc/apt/sources.list.d/ ~/answer 
```
Recreate the directory:
```
sudo mkdir /etc/apt/sources.list.d
```
Run apt update:
```
sudo apt update 
```
Remove the ~/answer directory:
```
sudo rm -r ~/answer
```

If the gist file used in the wget command above gets removed in the future, then you can copy the contents from here:

deb focal main restricted universe multiverse
deb-src focal main restricted universe multiverse
deb focal-updates main restricted universe multiverse
deb-src focal-updates main restricted universe multiverse
deb focal-security main restricted universe multiverse
deb-src focal-security main restricted universe multiverse
deb focal-backports main restricted universe multiverse
deb-src focal-backports main restricted universe multiverse
deb focal partner
deb-src focal partner