Невозможно установить синаптический модуль [дубликат]

Я не могу установить синаптический модуль в моей системе. Я пробовал следующее, но не повезло.

sudo apt-get update
sudo apt-get install synaptic

Я получаю вывод:

Reading package lists... Done 
Building dependency tree Reading state information... Done 
Package synaptic 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 'synaptic' has no installation candidate

Это сообщение об ошибке, которое я получаю при запуске sudo apt update:

cccc@cccc:~$ sudo apt update
[sudo] password for ccccc: 
Ign:1 http://gb.archive.ubuntu.com/ubuntu artful InRelease
Hit:2 http://archive.canonical.com/ubuntu artful InRelease
Ign:3 http://gb.archive.ubuntu.com/ubuntu artful-updates InRelease
Ign:4 http://gb.archive.ubuntu.com/ubuntu artful-backports InRelease
Ign:5 http://gb.archive.ubuntu.com/ubuntu artful-security InRelease
Err:6 http://gb.archive.ubuntu.com/ubuntu artful Release
  404  Not Found [IP: 91.189.88.149 80]
Err:7 http://gb.archive.ubuntu.com/ubuntu artful-updates Release
  404  Not Found [IP: 91.189.88.149 80]
Err:8 http://gb.archive.ubuntu.com/ubuntu artful-backports Release
  404  Not Found [IP: 91.189.88.149 80]
Err:9 http://gb.archive.ubuntu.com/ubuntu artful-security Release
  404  Not Found [IP: 91.189.88.149 80]
Reading package lists... Done                      
E: The repository 'http://gb.archive.ubuntu.com/ubuntu artful Release' 
does not have a Release file.
N: Updating from such a repository can't be done securely, and is 
therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user 
configuration details.
E: The repository 'http://gb.archive.ubuntu.com/ubuntu artful-updates 
Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is 
therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user 
configuration details.
E: The repository 'http://gb.archive.ubuntu.com/ubuntu artful- 
backports Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is 
therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user 
configuration details.
E: The repository 'http://gb.archive.ubuntu.com/ubuntu artful-security 
Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is 
therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user 
configuration details.

Кто-нибудь знает, как его установить?