ti@D8LXQt:/$ cd /etc/apt/
ti@D8LXQt:/etc/apt$ ls -al
total 52
drwxr-xr-x   6 root root  4096 Dec 11 22:23 .
drwxr-xr-x 134 root root 12288 Dec 12 16:50 ..
drwxr-xr-x   2 root root  4096 Dec 11 22:23 apt.conf.d
-rw-r--r--   1 root root    99 Sep 17 15:26 listchanges.conf
drwxr-xr-x   2 root root  4096 Mar 12  2016 preferences.d
-rw-r--r--   1 root root  1392 Dec 11 22:17 sources.list
-rw-r--r--   1 root root     0 Dec  1 17:05 sources.list~
drwxr-xr-x   2 root root  4096 Mar 12  2016 sources.list.d
-rw-r--r--   1 root root   981 Dec  2 23:56 sources.list.save
-rw-r--r--   1 root root  3483 Dec  7 00:00 trusted.gpg
-rw-r--r--   1 root root  1214 Dec  2 23:57 trusted.gpg~
drwxr-xr-x   2 root root  4096 Dec  2 23:57 trusted.gpg.d
ti@D8LXQt:/etc/apt$ cd preferences.d/
ti@D8LXQt:/etc/apt/preferences.d$ ls -al
total 8
drwxr-xr-x 2 root root 4096 Mar 12  2016 .
drwxr-xr-x 6 root root 4096 Dec 11 22:23 ..