*.save files are some kind of backup from your sources file these are not going to make any trouble, cause apt ignore these files silently.
nano uses similar files too, if you get a file named
*.save.1 it's because of
nano, These are emergency files, when
nano receives a
SIGTERM it will write its buffer to an emergency file to save you from data lost. For example if Terminal get closed while you have an open file or ssh connection fails (from
man nano notes section).
plesk.list.ai_back is plesk backup file.
apt ignores all except
*.list files . it show you some warning to let you know about these files however it also ignore some of them silently like
Take care of error:
As I said these are backup files, they have no impact on
apt and are not harmful so it's the best to keep them instead of removing them.
What I suggest is using
Dir::Ignore-Files-Silently option to add
*.ai_back files to silently ignored list. what will happen is
apt ignore these as before however it's not going to show you any warning anymore.
Create a file withing :
sudo nano /etc/apt/apt.conf.d/20-ignorebk
Dir::Ignore-Files-Silently:: "\.ai_back$"; to this file and save it.
Now you shouldn't get any warning about this kind files.