APT вообще не работает: «E: значение 'jessie' недопустимо для APT :: Default -Отпустите, поскольку такой выпуск недоступен в исходниках »[дубликат]

Я пытаюсь выполнить команду sudo apt-get install ssh , но когда это происходит, я получаю эту ошибку.

$ sudo apt-get install ssh
Reading package lists... Done
E: The value 'jessie' is invalid for APT::Default-Release as such a release is not available in the sources

когда я пытаюсь исправить apt update , я получаю следующее.

$ sudo apt update
Hit:1 http://security.ubuntu.com/ubuntu bionic-security InRelease
Hit:2 http://ca.archive.ubuntu.com/ubuntu bionic InRelease                                              
Hit:3 http://ca.archive.ubuntu.com/ubuntu bionic-updates InRelease                                      
Hit:4 http://ca.archive.ubuntu.com/ubuntu bionic-backports InRelease              
Ign:5 http://cdn-fastly.deb.debian.org/debian jessie-backports InRelease                                       
Ign:6 http://cdn-fastly.deb.debian.org/debian stretch InRelease
Err:7 http://cdn-fastly.deb.debian.org/debian jessie-backports Release
404  Not Found [IP: 151.101.124.204 80]
Get:8 http://cdn-fastly.deb.debian.org/debian stretch Release [118 kB]
Get:9 http://cdn-fastly.deb.debian.org/debian stretch Release.gpg [2,365 B]
Ign:9 http://cdn-fastly.deb.debian.org/debian stretch Release.gpg
Reading package lists... Done 
E: The repository 'http://httpredir.debian.org/debian jessie-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.
W: GPG error: http://cdn-fastly.deb.debian.org/debian stretch Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7638D0442B90D010 NO_PUBKEY 04EE7237B7D453EC NO_PUBKEY EF0F382A1A7B6500
E: The repository 'http://httpredir.debian.org/debian stretch Release' is not signed.
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 value 'jessie' is invalid for APT::Default-Release as such a release is not available in the sources

Кто-нибудь сталкивался с этим раньше? Есть ли способ просто стереть зависимости и начать заново?