Убедил пересесть друга на линух, он нагуглился до установки дебиана, и удалил /etc/apt/sources.list /etc/apt/sources.list.d
Генератором собрал дефолотный набор в sources.list
Пишу apt-get update.
Результат:
Ign:1 http://deb.debian.org/debian stable InRelease
Get:2 http://deb.debian.org/debian stable-updates InRelease [91.0 kB]
Get:3 http://deb.debian.org/debian-security stable/updates InRelease [94.3 kB]
Ign:2 http://deb.debian.org/debian stable-updates InRelease
Get:4 http://deb.debian.org/debian stable Release [118 kB]
Ign:3 http://deb.debian.org/debian-security stable/updates InRelease
Hit:5 https://download.sublimetext.com apt/stable/ InRelease
Get:6 http://deb.debian.org/debian stable Release.gpg [2,434 B]
Ign:6 http://deb.debian.org/debian stable Release.gpg
Hit:7 http://deb.debian.org/debian stable/main Sources
Ign:7 http://deb.debian.org/debian stable/main Sources
Hit:8 http://deb.debian.org/debian stable/contrib Sources
Ign:8 http://deb.debian.org/debian stable/contrib Sources
Hit:9 http://deb.debian.org/debian stable/non-free Sources
Ign:9 http://deb.debian.org/debian stable/non-free Sources
Hit:7 http://deb.debian.org/debian stable/main Sources
Ign:7 http://deb.debian.org/debian stable/main Sources
Hit:8 http://deb.debian.org/debian stable/contrib Sources
Ign:8 http://deb.debian.org/debian stable/contrib Sources
Hit:9 http://deb.debian.org/debian stable/non-free Sources
Ign:9 http://deb.debian.org/debian stable/non-free Sources
Hit:7 http://deb.debian.org/debian stable/main Sources
Hit:8 http://deb.debian.org/debian stable/contrib Sources
Hit:9 http://deb.debian.org/debian stable/non-free Sources
Fetched 306 kB in 3s (98.9 kB/s)
Reading package lists... Done
W: GPG error: http://deb.debian.org/debian stable-updates InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010
W: The repository 'http://deb.debian.org/debian stable-updates 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: GPG error: http://deb.debian.org/debian-security stable/updates InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 9D6D8F6BC857C906 NO_PUBKEY 8B48AD6246925553
W: The repository 'http://deb.debian.org/debian-security stable/updates 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: GPG error: http://deb.debian.org/debian stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010 NO_PUBKEY EF0F382A1A7B6500
W: The repository 'http://deb.debian.org/debian stable Release' 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.
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Ключи по совету генератора на каждый из репов прописаны, записались без ошибок. По итогу: sources.list забит дефолтными репами, а папка sources.list.d пустая. Спасибо!