Updating Ubuntu & understanding errors thrown by APT

Question

I am new to Ubuntu but I recently started using Ubuntu on my laptop for almost everything.

I executed sudo apt-get update to update my system, but I do not understand the output. I don't know whether the output is normal or there are some errors that I need to address.

Ign:1 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial InRelease
Ign:2 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial Release
Ign:3 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main amd64 Packages
Ign:4 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main i386 Packages
Ign:5 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main all Packages
Ign:6 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main Translation-en_US
Ign:7 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main Translation-en
Ign:8 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main amd64 DEP-11 Metadata
Ign:9 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main DEP-11 64x64 Icons
Ign:10 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted amd64 Packages
Ign:11 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted i386 Packages
Ign:12 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted all Packages
Ign:13 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted Translation-en_US
Ign:14 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted Translation-en
Ign:15 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted amd64 DEP-11 Metadata
Ign:16 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted DEP-11 64x64 Icons
Ign:3 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main amd64 Packages
Ign:4 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main i386 Packages
Ign:5 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main all Packages
Ign:6 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main Translation-en_US
Ign:7 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main Translation-en
Ign:8 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main amd64 DEP-11 Metadata
Ign:9 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main DEP-11 64x64 Icons
Ign:10 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted amd64 Packages
Ign:11 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted i386 Packages
Ign:12 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted all Packages
Ign:13 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted Translation-en_US
Ign:14 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted Translation-en
Ign:15 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted amd64 DEP-11 Metadata
Ign:16 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted DEP-11 64x64 Icons
Ign:3 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main amd64 Packages
Ign:4 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main i386 Packages
Ign:5 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main all Packages
Ign:6 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main Translation-en_US
Ign:7 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main Translation-en
Ign:8 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main amd64 DEP-11 Metadata
Ign:9 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main DEP-11 64x64 Icons
Ign:10 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted amd64 Packages
Ign:11 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted i386 Packages
Ign:12 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted all Packages
Ign:13 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted Translation-en_US
Ign:14 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted Translation-en
Ign:15 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted amd64 DEP-11 Metadata
Ign:16 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted DEP-11 64x64 Icons
Ign:3 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main amd64 Packages
Ign:4 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main i386 Packages
Ign:5 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main all Packages
Ign:6 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main Translation-en_US
Ign:7 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main Translation-en
Ign:8 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main amd64 DEP-11 Metadata
Ign:9 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main DEP-11 64x64 Icons
Ign:10 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted amd64 Packages
Ign:11 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted i386 Packages
Ign:12 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted all Packages
Ign:13 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted Translation-en_US
Ign:14 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted Translation-en
Ign:15 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted amd64 DEP-11 Metadata
Ign:16 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted DEP-11 64x64 Icons
Ign:3 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main amd64 Packages
Ign:4 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main i386 Packages
Ign:5 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main all Packages
Ign:6 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main Translation-en_US
Ign:7 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main Translation-en
Ign:8 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main amd64 DEP-11 Metadata
Ign:9 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main DEP-11 64x64 Icons
Ign:10 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted amd64 Packages
Ign:11 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted i386 Packages
Ign:12 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted all Packages
Ign:13 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted Translation-en_US
Ign:14 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted Translation-en
Ign:15 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted amd64 DEP-11 Metadata
Ign:16 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/restricted DEP-11 64x64 Icons
Err:3 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main amd64 Packages
  Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
Ign:4 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main i386 Packages
Ign:17 http://dl.google.com/linux/chrome/deb stable InRelease
Get:18 http://dl.google.com/linux/chrome/deb stable Release [1,189 B]          
Get:19 http://dl.google.com/linux/chrome/deb stable Release.gpg [819 B]        
Hit:20 http://ppa.launchpad.net/alessandro-strada/ppa/ubuntu xenial InRelease  
Get:21 http://dl.google.com/linux/chrome/deb stable/main amd64 Packages [1,407 B]
Hit:22 https://download.01.org/gfx/ubuntu/16.04/main xenial InRelease          
Ign:23 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial InRelease      
Get:24 http://ppa.launchpad.net/hanipouspilot/rtlwifi/ubuntu xenial InRelease [18.1 kB]
Ign:24 http://ppa.launchpad.net/hanipouspilot/rtlwifi/ubuntu xenial InRelease  
Hit:25 http://ppa.launchpad.net/noobslab/themes/ubuntu xenial InRelease        
Hit:26 http://ppa.launchpad.net/numix/ppa/ubuntu xenial InRelease              
Get:27 http://ppa.launchpad.net/papirus/papirus/ubuntu xenial InRelease [18.0 kB]
Hit:28 http://ppa.launchpad.net/snwh/pulp/ubuntu xenial InRelease              
Hit:29 http://ppa.launchpad.net/ubuntu-x-swat/updates/ubuntu xenial InRelease  
Hit:30 http://ppa.launchpad.net/webupd8team/atom/ubuntu xenial InRelease       
Hit:31 http://ppa.launchpad.net/webupd8team/java/ubuntu xenial InRelease       
Ign:32 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial Release        
Get:33 http://ppa.launchpad.net/papirus/papirus/ubuntu xenial/main amd64 Packages [2,496 B]
Get:34 http://ppa.launchpad.net/papirus/papirus/ubuntu xenial/main i386 Packages [2,496 B]
Ign:35 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main amd64 Packages
Ign:36 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main i386 Packages
Ign:37 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main all Packages
Ign:38 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main Translation-en_US
Ign:39 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main Translation-en
Ign:40 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:41 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main DEP-11 64x64 Icons
Ign:35 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main amd64 Packages
Hit:42 http://archive.ubuntu.com/ubuntu xenial InRelease                       
Hit:43 http://archive.canonical.com/ubuntu xenial InRelease                    
Get:44 http://archive.ubuntu.com/ubuntu xenial-updates InRelease [102 kB]      
Hit:45 http://archive.canonical.com xenial InRelease                           
Ign:46 http://repo.vivaldi.com/stable/deb stable InRelease                     
Hit:47 http://repo.vivaldi.com/stable/deb stable Release                       
Ign:36 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main i386 Packages
Get:49 https://deb.nodesource.com/node_6.x xenial InRelease [4,634 B]          
Ign:37 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main all Packages
Get:50 http://archive.ubuntu.com/ubuntu xenial-backports InRelease [102 kB]
Hit:51 https://packages.microsoft.com/repos/vscode stable InRelease            
Hit:52 https://download.sublimetext.com apt/stable/ InRelease                  
Get:53 https://deb.nodesource.com/node_6.x xenial/main amd64 Packages [1,003 B]
Ign:38 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main Translation-en_US
Get:54 https://deb.nodesource.com/node_6.x xenial/main i386 Packages [1,001 B] 
Get:55 http://archive.ubuntu.com/ubuntu xenial-security InRelease [102 kB]     
Ign:39 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main Translation-en
Hit:56 https://deb.opera.com/opera-stable stable InRelease                     
Get:57 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages [678 kB]
Ign:40 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main amd64 DEP-11 Metadata
Get:58 https://packagecloud.io/slacktechnologies/slack/debian jessie InRelease [23.5 kB]
Ign:41 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main DEP-11 64x64 Icons
Get:59 http://archive.ubuntu.com/ubuntu xenial-updates/main i386 Packages [637 kB]
Get:60 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 DEP-11 Metadata [307 kB]
Ign:35 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main amd64 Packages
Get:61 http://archive.ubuntu.com/ubuntu xenial-updates/main DEP-11 64x64 Icons [213 kB]
Get:62 http://archive.ubuntu.com/ubuntu xenial-updates/universe amd64 Packages [564 kB]
Get:63 https://packagecloud.io/slacktechnologies/slack/debian jessie/main amd64 Packages [8,044 B]
Ign:36 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main i386 Packages
Get:64 http://archive.ubuntu.com/ubuntu xenial-updates/universe i386 Packages [529 kB]
Ign:65 https://packagecloud.io/slacktechnologies/slack/debian jessie/main i386 Packages
Ign:37 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main all Packages
Get:66 http://archive.ubuntu.com/ubuntu xenial-updates/universe amd64 DEP-11 Metadata [185 kB]
Get:67 http://archive.ubuntu.com/ubuntu xenial-updates/universe DEP-11 64x64 Icons [259 kB]
Get:65 https://packagecloud.io/slacktechnologies/slack/debian jessie/main i386 Packages [5,003 B]
Get:68 http://archive.ubuntu.com/ubuntu xenial-updates/multiverse amd64 DEP-11 Metadata [5,892 B]
Get:69 http://archive.ubuntu.com/ubuntu xenial-backports/main amd64 DEP-11 Metadata [3,328 B]
Get:70 http://archive.ubuntu.com/ubuntu xenial-backports/universe amd64 DEP-11 Metadata [4,676 B]
Get:71 http://archive.ubuntu.com/ubuntu xenial-security/main amd64 DEP-11 Metadata [62.5 kB]
Get:72 http://archive.ubuntu.com/ubuntu xenial-security/main DEP-11 64x64 Icons [62.6 kB]
Get:73 http://archive.ubuntu.com/ubuntu xenial-security/universe amd64 DEP-11 Metadata [51.4 kB]
Get:74 http://archive.ubuntu.com/ubuntu xenial-security/universe DEP-11 64x64 Icons [70.8 kB]
Ign:38 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main Translation-en_US
Ign:39 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main Translation-en
Ign:40 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:41 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main DEP-11 64x64 Icons
Ign:35 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main amd64 Packages
Ign:36 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main i386 Packages
Ign:37 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main all Packages
Ign:38 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main Translation-en_US
Ign:39 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main Translation-en
Ign:40 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:41 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main DEP-11 64x64 Icons
Ign:35 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main amd64 Packages
Ign:36 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main i386 Packages
Ign:37 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main all Packages
Ign:38 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main Translation-en_US
Ign:39 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main Translation-en
Ign:40 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:41 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main DEP-11 64x64 Icons
Err:35 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main amd64 Packages                                                                  
  404  Not Found
Ign:36 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main i386 Packages                                                                   
Ign:37 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main all Packages                                                                    
Ign:38 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main Translation-en_US                                                               
Ign:39 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main Translation-en                                                                  
Ign:40 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main amd64 DEP-11 Metadata                                                           
Ign:41 http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial/main DEP-11 64x64 Icons                                                              
Fetched 4,027 kB in 16s (250 kB/s)                                                                                                                   
Reading package lists... Done
W: Target Sources (main/source/Sources) is configured multiple times in /etc/apt/sources.list.d/ubuntu-x-swat-ubuntu-updates-xenial.list:2 and /etc/apt/sources.list.d/ubuntu-x-swat-ubuntu-updates-xenial.list:3
W: The repository 'cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: https://download.01.org/gfx/ubuntu/16.04/main/dists/xenial/InRelease: Signature by key 09D6EF97BFB38E916EF060E756A3DEF863961D39 uses weak digest algorithm (SHA1)
W: GPG error: http://ppa.launchpad.net/hanipouspilot/rtlwifi/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7036069A2F22E44A
W: The repository 'http://ppa.launchpad.net/hanipouspilot/rtlwifi/ubuntu xenial InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: The repository 'http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2)/dists/xenial/main/binary-amd64/Packages  Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
E: Failed to fetch http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu/dists/xenial/main/binary-amd64/Packages  404  Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.
W: Target Sources (main/source/Sources) is configured multiple times in /etc/apt/sources.list.d/ubuntu-x-swat-ubuntu-updates-xenial.list:2 and /etc/apt/sources.list.d/ubuntu-x-swat-ubuntu-updates-xenial.list:3

Update: After following suggestions provided by Zanna and suggestions from all the links included in her answer, my output is as follows:

sudo apt-get update
Hit:1 http://archive.canonical.com xenial InRelease                            
Hit:2 http://archive.ubuntu.com/ubuntu xenial InRelease                        
Hit:3 http://ppa.launchpad.net/alessandro-strada/ppa/ubuntu xenial InRelease
Get:4 http://archive.ubuntu.com/ubuntu xenial-updates InRelease [102 kB]       
Hit:5 https://download.sublimetext.com apt/stable/ InRelease                   
Hit:6 http://ppa.launchpad.net/noobslab/themes/ubuntu xenial InRelease         
Hit:7 https://deb.opera.com/opera-stable stable InRelease                      
Hit:8 http://ppa.launchpad.net/numix/ppa/ubuntu xenial InRelease        
Get:9 http://archive.ubuntu.com/ubuntu xenial-backports InRelease [102 kB]     
Hit:10 http://ppa.launchpad.net/papirus/papirus/ubuntu xenial InRelease        
Hit:11 https://download.01.org/gfx/ubuntu/16.04/main xenial InRelease          
Hit:12 https://deb.nodesource.com/node_6.x xenial InRelease
Hit:13 https://packages.microsoft.com/repos/vscode stable InRelease
Hit:14 https://packagecloud.io/slacktechnologies/slack/debian jessie InRelease                     
Get:15 http://archive.ubuntu.com/ubuntu xenial-security InRelease [102 kB]                         
Hit:16 http://ppa.launchpad.net/snwh/pulp/ubuntu xenial InRelease                     
Hit:17 http://ppa.launchpad.net/ubuntu-x-swat/updates/ubuntu xenial InRelease                                    
Hit:18 http://ppa.launchpad.net/ubuntuhandbook1/apps/ubuntu xenial InRelease   
Hit:19 http://ppa.launchpad.net/webupd8team/atom/ubuntu xenial InRelease       
Hit:20 http://ppa.launchpad.net/webupd8team/java/ubuntu xenial InRelease       
Fetched 306 kB in 5s (52.6 kB/s)                   
Reading package lists... Done
W: https://download.01.org/gfx/ubuntu/16.04/main/dists/xenial/InRelease: Signature by key 09D6EF97BFB38E916EF060E756A3DEF863961D39 uses weak digest algorithm (SHA1)

The AskUbuntu format works best if you ask a single, specific question. Asking "What do these 8 warnings and 3 errors mean?" is 11 questions. Neither the question nor the answers are likely to help future users. Read each line that you don't understand carefully, then search AskUbuntu for key parts of the text - those warnings and errors have been explained before, multiple times. You have multiple problems, most (not all) caused by your PPAs, and each must be fixed separately...but all are quite easy to fix. — user535733, Dec 09 '17 at 00:35
I don't think it makes sense to close this question as too broad. If hp1988 were to ask about those error messages individually, we would probably ask them to post the full output to give us a full picture of what is going on. And I disagree that it would not be helpful to explain all those errors in an answer. For one thing, they all relate to the same type of problem: outdated repositories. — Zanna, Dec 10 '17 at 11:57

score 2 · Accepted Answer · edited Dec 10 '17 at 17:50

When you run sudo apt-get update, the APT program reads the file

/etc/apt/sources.list

and files in

/etc/apt/sources.list.d/

and attempts to download index files from the repositories specified there to update the dpkg database on your system so that it contains accurate and current information about the contents of those repositories.

Errors thrown by APT often relate to the contents of these files.

The issues in your output all (apart from the weak digest algorithm warning) relate to repositories you cannot use on 16.04. This suggests that your repository listings are all misconfigured and that you should probably regenerate your sources from scratch! If you have only just installed Ubuntu, and you have never added a PPA, I suggest you delete all the files in /etc/apt/sources.list.d:

sudo rm /etc/apt/sources.list.d/*

Then use one of the methods described here How do I restore the default repositories? to set up your repositories cleanly.

However, to answer your question...

First you have a number of lines with

Ign: cdrom://Ubuntu [...]

Ign means that APT tried to download a file and could not find it at the given address, but not finding it was not important enough to prevent APT from continuing. This is not necessarily a problem. APT might just be checking for files that don't need to exist. A large number of Ign lines might indicate a problem though, as it suggests you have obsolete repositories configured, or a wrong configuration, because many requested files could not be found.

See:

How do Ign and Hit affect apt-get update? on Super User.

Then you got this related error:

Err:3 cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial/main amd64 Packages
Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs

which links to this warning and information:

W: The repository 'cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2) xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.

And this error:

E: Failed to fetch cdrom://Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2)/dists/xenial/main/binary-amd64/Packages  Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs

These messages are caused by a line in your /etc/apt/sources.list

deb cdrom [...]

This line should start with a # to cause it to be ignored, i.e. it should be "commented out". You can edit the sources.list file yourself, using a text editor opened with root privileges, e.g.:

sudo nano -w /etc/apt/sources.list

put a # in front of deb cdrom and save the file.

Or you can use the Software Sources GUI in Software and Updates.

After you have removed this repository, the Ign lines that mention cdrom should also disappear from your sudo apt-get update output.

See:

Failed to download repository information due to missing CDROM
the man page for apt-cdrom if you are interested in the rest of the error message

You also have many Ign lines relating to a PPA

Ign: http://ppa.launchpad.net/gwibber-daily

And some errors relating to it which are very similar to the cdrom errors. The gwibber-daily repository has not been updated for a very long time, and has no packages for your version of Ubuntu. You need to remove that PPA from your sources. PPA repository files are usually in /etc/apt/sources.list.d. You can get rid of the errors by deleting the file that relates to gwibber-daily from /etc/apt/sources.list.d, or again, by editing your sources from the GUI.

See:

How can I fix a 404 Error when using a PPA or updating my package lists?
Error Updating: izx/askubuntu/ubuntu xenial Release' does not have a Release file (I am looking for a better question/answer to link to - if any readers have a suggestion, please edit/comment)

You also have this warning:

W: Target Sources (main/source/Sources) is configured multiple times in /etc/apt/sources.list.d/ubuntu-x-swat-ubuntu-updates-xenial.list:2 and /etc/apt/sources.list.d/ubuntu-x-swat-ubuntu-updates-xenial.list:3

This means that the same repository is mentioned twice in your source configuration files. You can remove the error by deleting either (or both, if you don't want to use that repository) of the files mentioned, or in the Software Sources GUI.

See:

How can I automatically fix W: Target Packages ... is configured multiple times?

You also have

W: https://download.01.org/gfx/ubuntu/16.04/main/dists/xenial/InRelease: Signature by key 09D6EF97BFB38E916EF060E756A3DEF863961D39 uses weak digest algorithm (SHA1)

This is probably harmless; it just means the key used to sign the repository uses a less robust checksum method than APT's high standards expect. The repository does have a branch for 16.04, so you may not want to remove it. The warning will not prevent APT from downloading packages from that repository.

See:

How to fix apt: Signature by key uses weak digest algorithm (SHA1)?

Finally you have this well-known warning:

W: GPG error: http://ppa.launchpad.net/hanipouspilot/rtlwifi/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7036069A2F22E44A
W: The repository 'http://ppa.launchpad.net/hanipouspilot/rtlwifi/ubuntu xenial InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.

It may sometimes be appropriate to solve this error by adding the key, but that would not solve the underlying problem, which is that, like the other repositories, this one has no packages for 16.04. You should remove this PPA from your sources too.

Thank you so much @Zanna for taking time to answer my question. I really appreciate your efforts in explaining me about all the errors. I also visited links you provided for specific errors.After following your suggestions & suggestions provided in the links I managed to get the output (updated question with the new output) which is much more cleaner than what I used to have before. — AJS_fan, Dec 10 '17 at 17:15
Zanna I still have one question at this point. After following all suggestions how do I make sure that I continue to receive Ubuntu 16.04 updates ? In other words , how do I verify that Ubuntu (Ubuntu OS & not third party s/w(s) such as chrome/opera etc) is updated when I execute sudo apt-get upgrade ? — AJS_fan, Dec 10 '17 at 17:18
@hp1988 you're very welcome! You should always update before you upgrade. I suggest using sudo apt update rather than sudo apt-get update, because apt provides feedback, for example all packages are up to date or 2 packages can be upgraded, run 'apt list --upgradeable' to see them. The new output you posted looks healthy - the only possible concern is that you might have software that you installed, but then removed the repository for. Do you have any reason to believe that that is the case? — Zanna, Dec 10 '17 at 17:26

Updating Ubuntu & understanding errors thrown by APT

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