mjhjmtu

I was installing the Atom text editor on Ubuntu 18.04.1 LTS Bionic Beaver using the command:-

sudo apt-get install atom

I stopped the installation process and now whenever I run the command:-

sudo apt update

The following is the output:-

Hit:1 http://ppa.launchpad.net/webupd8team/atom/ubuntu bionic InRelease
Reading package lists... Done
Building dependency tree 
Reading state information... Done
All packages are up to date.

Whenever I try to install Atom again, I get the following output:-

Reading package lists... Done
Building dependency tree 
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 atom : Depends: gvfs-bin but it is not installable
E: Unable to correct problems, you have held broken packages.

Now, whenever I try to install a package from the terminal using:

sudo apt-get install "package-name"

I get some output showing: This package has no installation candidate.

For example, if I install rpm, the output is:-

Reading package lists... Done
Building dependency tree 
Reading state information... Done
Package rpm is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'rpm' has no installation candidate

[*Edit]
Now, when I run sudo apt update everything is fine but there's this weird output at the last:-

E: Some index files failed to download. They have been ignored, or old ones used instead.
W: Target Packages (main/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target Translations (main/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target DEP-11 (main/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target DEP-11 (main/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target DEP-11-icons (main/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target CNF (main/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target CNF (main/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target Packages (restricted/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target Packages (restricted/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target Translations (restricted/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target Translations (restricted/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target DEP-11 (restricted/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target DEP-11 (restricted/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target DEP-11-icons (restricted/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target CNF (restricted/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target CNF (restricted/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:5 and /etc/apt/sources.list.d/official-package-repositories.list:5
W: Target Packages (universe/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:16 and /etc/apt/sources.list.d/official-package-repositories.list:16
W: Target Packages (universe/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:16 and /etc/apt/sources.list.d/official-package-repositories.list:16
W: Target Translations (universe/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:16 and /etc/apt/sources.list.d/official-package-repositories.list:16
W: Target Translations (universe/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:16 and /etc/apt/sources.list.d/official-package-repositories.list:16
W: Target DEP-11 (universe/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:16 and /etc/apt/sources.list.d/official-package-repositories.list:16
W: Target DEP-11 (universe/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:16 and /etc/apt/sources.list.d/official-package-repositories.list:16
W: Target DEP-11-icons (universe/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:16 and /etc/apt/sources.list.d/official-package-repositories.list:16
W: Target CNF (universe/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:16 and /etc/apt/sources.list.d/official-package-repositories.list:16
W: Target CNF (universe/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:16 and /etc/apt/sources.list.d/official-package-repositories.list:16
W: Target Packages (multiverse/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:26 and /etc/apt/sources.list.d/official-package-repositories.list:26
W: Target Packages (multiverse/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:26 and /etc/apt/sources.list.d/official-package-repositories.list:26
W: Target Translations (multiverse/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:26 and /etc/apt/sources.list.d/official-package-repositories.list:26
W: Target Translations (multiverse/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:26 and /etc/apt/sources.list.d/official-package-repositories.list:26
W: Target DEP-11 (multiverse/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:26 and /etc/apt/sources.list.d/official-package-repositories.list:26
W: Target DEP-11 (multiverse/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:26 and /etc/apt/sources.list.d/official-package-repositories.list:26
W: Target DEP-11-icons (multiverse/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:26 and /etc/apt/sources.list.d/official-package-repositories.list:26
W: Target CNF (multiverse/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:26 and /etc/apt/sources.list.d/official-package-repositories.list:26
W: Target CNF (multiverse/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:26 and /etc/apt/sources.list.d/official-package-repositories.list:26
W: Target Packages (main/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target Translations (main/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target DEP-11 (main/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target DEP-11 (main/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target DEP-11-icons (main/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target CNF (main/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target CNF (main/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target Packages (restricted/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target Packages (restricted/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target Translations (restricted/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target Translations (restricted/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target DEP-11 (restricted/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target DEP-11 (restricted/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target DEP-11-icons (restricted/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target CNF (restricted/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target CNF (restricted/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:10 and /etc/apt/sources.list.d/official-package-repositories.list:10
W: Target Packages (universe/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:18 and /etc/apt/sources.list.d/official-package-repositories.list:18
W: Target Packages (universe/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:18 and /etc/apt/sources.list.d/official-package-repositories.list:18
W: Target Translations (universe/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:18 and /etc/apt/sources.list.d/official-package-repositories.list:18
W: Target Translations (universe/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:18 and /etc/apt/sources.list.d/official-package-repositories.list:18
W: Target DEP-11 (universe/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:18 and /etc/apt/sources.list.d/official-package-repositories.list:18
W: Target DEP-11 (universe/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:18 and /etc/apt/sources.list.d/official-package-repositories.list:18
W: Target DEP-11-icons (universe/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:18 and /etc/apt/sources.list.d/official-package-repositories.list:18
W: Target CNF (universe/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:18 and /etc/apt/sources.list.d/official-package-repositories.list:18
W: Target CNF (universe/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:18 and /etc/apt/sources.list.d/official-package-repositories.list:18
W: Target Packages (multiverse/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:28 and /etc/apt/sources.list.d/official-package-repositories.list:28
W: Target Packages (multiverse/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:28 and /etc/apt/sources.list.d/official-package-repositories.list:28
W: Target Translations (multiverse/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:28 and /etc/apt/sources.list.d/official-package-repositories.list:28
W: Target Translations (multiverse/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:28 and /etc/apt/sources.list.d/official-package-repositories.list:28
W: Target DEP-11 (multiverse/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:28 and /etc/apt/sources.list.d/official-package-repositories.list:28
W: Target DEP-11 (multiverse/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:28 and /etc/apt/sources.list.d/official-package-repositories.list:28
W: Target DEP-11-icons (multiverse/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:28 and /etc/apt/sources.list.d/official-package-repositories.list:28
W: Target CNF (multiverse/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:28 and /etc/apt/sources.list.d/official-package-repositories.list:28
W: Target CNF (multiverse/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:28 and /etc/apt/sources.list.d/official-package-repositories.list:28
W: Target Packages (main/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Translations (main/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target DEP-11 (main/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target DEP-11 (main/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target DEP-11-icons (main/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target CNF (main/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target CNF (main/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Packages (restricted/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Packages (restricted/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Translations (restricted/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Translations (restricted/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target DEP-11 (restricted/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target DEP-11 (restricted/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target DEP-11-icons (restricted/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target CNF (restricted/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target CNF (restricted/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Packages (universe/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Packages (universe/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Translations (universe/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Translations (universe/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target DEP-11 (universe/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target DEP-11 (universe/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target DEP-11-icons (universe/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target CNF (universe/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target CNF (universe/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Packages (multiverse/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Packages (multiverse/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Translations (multiverse/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Translations (multiverse/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target DEP-11 (multiverse/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target DEP-11 (multiverse/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target DEP-11-icons (multiverse/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target CNF (multiverse/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target CNF (multiverse/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:36 and /etc/apt/sources.list.d/official-package-repositories.list:36
W: Target Packages (main/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target Translations (main/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target DEP-11 (main/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target DEP-11 (main/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target DEP-11-icons (main/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target CNF (main/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target CNF (main/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target Packages (restricted/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target Packages (restricted/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target Translations (restricted/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target Translations (restricted/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target DEP-11 (restricted/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target DEP-11 (restricted/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target DEP-11-icons (restricted/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target CNF (restricted/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target CNF (restricted/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:46 and /etc/apt/sources.list.d/official-package-repositories.list:46
W: Target Packages (universe/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:48 and /etc/apt/sources.list.d/official-package-repositories.list:48
W: Target Packages (universe/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:48 and /etc/apt/sources.list.d/official-package-repositories.list:48
W: Target Translations (universe/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:48 and /etc/apt/sources.list.d/official-package-repositories.list:48
W: Target Translations (universe/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:48 and /etc/apt/sources.list.d/official-package-repositories.list:48
W: Target DEP-11 (universe/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:48 and /etc/apt/sources.list.d/official-package-repositories.list:48
W: Target DEP-11 (universe/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:48 and /etc/apt/sources.list.d/official-package-repositories.list:48
W: Target DEP-11-icons (universe/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:48 and /etc/apt/sources.list.d/official-package-repositories.list:48
W: Target CNF (universe/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:48 and /etc/apt/sources.list.d/official-package-repositories.list:48
W: Target CNF (universe/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:48 and /etc/apt/sources.list.d/official-package-repositories.list:48
W: Target Packages (multiverse/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list:50 and /etc/apt/sources.list.d/official-package-repositories.list:50
W: Target Packages (multiverse/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:50 and /etc/apt/sources.list.d/official-package-repositories.list:50
W: Target Translations (multiverse/i18n/Translation-en_IN) is configured multiple times in /etc/apt/sources.list:50 and /etc/apt/sources.list.d/official-package-repositories.list:50
W: Target Translations (multiverse/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:50 and /etc/apt/sources.list.d/official-package-repositories.list:50
W: Target DEP-11 (multiverse/dep11/Components-i386.yml) is configured multiple times in /etc/apt/sources.list:50 and /etc/apt/sources.list.d/official-package-repositories.list:50
W: Target DEP-11 (multiverse/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list:50 and /etc/apt/sources.list.d/official-package-repositories.list:50
W: Target DEP-11-icons (multiverse/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list:50 and /etc/apt/sources.list.d/official-package-repositories.list:50
W: Target CNF (multiverse/cnf/Commands-i386) is configured multiple times in /etc/apt/sources.list:50 and /etc/apt/sources.list.d/official-package-repositories.list:50
W: Target CNF (multiverse/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:50 and /etc/apt/sources.list.d/official-package-repositories.list:50

It looks like the main repository list file has been deleted.

The following command will provide the original base /etc/apt/sources.list file obtained from the downloaded image file for Ubuntu 18.04 LTS.

sudo echo -e "# Sources.list obtained directly from the downloaded Ubuntu iso image filendeb http://archive.ubuntu.com/ubuntu/ bionic main restrictedndeb http://security.ubuntu.com/ubuntu/ bionic-security main restrictedndeb http://archive.ubuntu.com/ubuntu/ bionic-updates main restricted" > /etc/apt/sources.list

Once the main repo source file has been created, you will need to update the apt-cache:

sudo apt-get update

At this point, you may get errors depending on whether some of your PPAs conflict with the main repo. It is advisable to disable all your PPAs before attempting to fix your repo issues. However, that may also produce errors if some of the software installed from the individual PPAs require newer libraries than the official Ubuntu.

If you don't encounter any errors when updating, you might be OK. However, you may need to enable the less restricted repo list below. You may replace the contents of /etc/apt/sources.list with the following repo list:

#deb cdrom:[Ubuntu 18.04 LTS _Bionic Beaver_ - Release amd64 (20180426)]/ bionic main restricted

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://us.archive.ubuntu.com/ubuntu/ bionic main restricted
# deb-src http://us.archive.ubuntu.com/ubuntu/ bionic main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ bionic-updates main restricted
# deb-src http://us.archive.ubuntu.com/ubuntu/ bionic-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ bionic universe
# deb-src http://us.archive.ubuntu.com/ubuntu/ bionic universe
deb http://us.archive.ubuntu.com/ubuntu/ bionic-updates universe
# deb-src http://us.archive.ubuntu.com/ubuntu/ bionic-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://us.archive.ubuntu.com/ubuntu/ bionic multiverse
# deb-src http://us.archive.ubuntu.com/ubuntu/ bionic multiverse
deb http://us.archive.ubuntu.com/ubuntu/ bionic-updates multiverse
# deb-src http://us.archive.ubuntu.com/ubuntu/ bionic-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse
# deb-src http://us.archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu bionic partner
# deb-src http://archive.canonical.com/ubuntu bionic partner

deb http://security.ubuntu.com/ubuntu bionic-security main restricted
# deb-src http://security.ubuntu.com/ubuntu bionic-security main restricted
deb http://security.ubuntu.com/ubuntu bionic-security universe
# deb-src http://security.ubuntu.com/ubuntu bionic-security universe
deb http://security.ubuntu.com/ubuntu bionic-security multiverse
# deb-src http://security.ubuntu.com/ubuntu bionic-security multiverse

External Links:

Ubuntu 18.04 ISO (2GB)

Gist Source for complete Ubuntu 18.04 LTS /etc/sources.list (plain text)

@RubberStamp ... I was unable to comment in the comment-section. It said user does not have permission to comment on this post.

Anyway, not only for atom, but for any package I try to install the output is either

E: Unable to locate package "package-name"

or

E: Package "package-name" has no installation candidate