Eu corro sudo apt update mas recebo o seguinte.
Não há repositório TMSU no meu sources.list , mas ainda recebo http://ppa.launchpad.net/tmsu/daily/ubuntu artful Release' does not have a Release file .
Há também algum problema em acessar os backports do Stretch
Get:63 http://ftp.fr.debian.org/debian unstable/main Translation-en [5,789 kB]
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/tmsu/daily/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: Could not open file /var/lib/apt/lists/http.debian.net_debian_dists_stretch-backports_main_binary-amd64_Packages.diff_Index - open (2: No such file or directory)
E: Could not open file /var/lib/apt/lists/http.debian.net_debian_dists_stretch-backports_main_binary-i386_Packages.diff_Index - open (2: No such file or directory)
E: The repository 'http://httpredir.debian.org/debian stretch Release' is no longer 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.
Meu /etc/apt/sources.list
#
deb http://ftp.fi.debian.org/debian/ stretch main
# deb http://ftp.us.debian.org/debian/ stretch main
deb-src http://ftp.fi.debian.org/debian/ stretch main
# deb-src http://ftp.us.debian.org/debian/ stretch main
deb http://security.debian.org/ stretch/updates main contrib
deb-src http://security.debian.org/ stretch/updates main contrib
# stretch-updates, previously known as 'volatile'
deb http://ftp.fi.debian.org/debian/ stretch-updates main contrib
# deb http://ftp.us.debian.org/debian/ stretch-updates main contrib
deb-src http://ftp.fi.debian.org/debian/ stretch-updates main contrib
# deb-src http://ftp.us.debian.org/debian/ stretch-updates main contrib
# stretch backports
deb http://http.debian.net/debian stretch-backports main contrib non-free
deb http://httpredir.debian.org/debian/ stretch main contrib
# NO package
# deb http://cran.wu.ac.at/bin/linux/debian stretch-cran3/
# https://unix.stackexchange.com/a/366085/16920
deb http://ftp.fr.debian.org/debian unstable main
# https://cran.r-project.org/
# http://stackoverflow.com/q/44026585/54964
deb https://ftp.eenet.ee/pub/cran/bin/linux/debian stretch-cran34/
deb [arch=amd64] https://download.docker.com/linux/debian stretch stable
# deb-src [arch=amd64] https://download.docker.com/linux/debian stretch stable
Testando a proposta do sgargel
masi@masi:/etc/apt/sources.list.d$ grep -R tmsu
tmsu-ubuntu-daily-artful.list:deb http://ppa.launchpad.net/tmsu/daily/ubuntu artful main
tmsu-ubuntu-daily-artful.list:# deb-src http://ppa.launchpad.net/tmsu/daily/ubuntu artful main
OS: Debian 9
O ppa.launchpad.net/tmsu/daily/ubuntu deve funcionar apenas no derivado do Ubuntu, da saída de grep -R tmsu ( @sagargel comentário), o ppa ainda existe em /etc/apt/sources.list.d , você deve removê-lo manualmente:
sudo rm -i /etc/apt/sources.list.d/tmsu-ubuntu-daily-artful.list
sudo apt update