Peut être que la réponse de cette commande pourras aider :
ls -lR /etc/apt
/etc/apt:
total 28
drwxr-xr-x 2 root root 4096 mars 29 09:23 apt.conf.d
drwxr-xr-x 2 root root 4096 mars 29 10:45 preferences.d
-rw-r–r-- 1 root root 1600 mars 29 10:16 sources.list
-rw-r–r-- 1 root root 0 nov. 2 2017 sources.list~
drwxr-xr-x 2 root root 4096 mars 29 10:18 sources.list.d
-rw-r–r-- 1 root root 2206 janv. 3 2018 trusted.gpg
-rw-r–r-- 1 root root 3494 janv. 3 2018 trusted.gpg~
drwxr-xr-x 2 root root 4096 janv. 3 2018 trusted.gpg.d
/etc/apt/apt.conf.d:
total 32
-rw-r–r-- 1 root root 82 nov. 2 2017 00CDMountPoint
-rw-r–r-- 1 root root 33 nov. 2 2017 00InstallRecommends
-rw-r–r-- 1 root root 40 nov. 2 2017 00trustcdrom
-rw-r–r-- 1 root root 769 sept. 13 2017 01autoremove
-r–r--r-- 1 root root 1171 janv. 3 2018 01autoremove-kernels
-rw-r–r-- 1 root root 627 nov. 5 10:32 01autoremove-postgresql
-rw-r–r-- 1 root root 182 mai 21 2017 70debconf
-rw-r–r-- 1 root root 80 janv. 3 2018 90cloud-init-pipelining
/etc/apt/preferences.d:
total 0
/etc/apt/sources.list.d:
total 4
-rw-r–r-- 1 root root 63 mars 29 10:18 pgdg.list
/etc/apt/trusted.gpg.d:
total 48
lrwxrwxrwx 1 root root 56 janv. 3 2018 apt.postgresql.org.gpg -> /usr/share/postgresql-common/pgdg/apt.postgresql.org.gpg
-rw-r–r-- 1 root root 5138 mai 25 2017 debian-archive-jessie-automatic.gpg
-rw-r–r-- 1 root root 5147 mai 25 2017 debian-archive-jessie-security-automatic.gpg
-rw-r–r-- 1 root root 2775 mai 25 2017 debian-archive-jessie-stable.gpg
-rw-r–r-- 1 root root 7483 mai 25 2017 debian-archive-stretch-automatic.gpg
-rw-r–r-- 1 root root 7492 mai 25 2017 debian-archive-stretch-security-automatic.gpg
-rw-r–r-- 1 root root 2275 mai 25 2017 debian-archive-stretch-stable.gpg
-rw-r–r-- 1 root root 3780 mai 25 2017 debian-archive-wheezy-automatic.gpg
-rw-r–r-- 1 root root 2851 mai 25 2017 debian-archive-wheezy-stable.gpg