I have some strange issue here. Update Manager and Synaptic are not able to download packages, but apt has no problem at all.
Update Manager says exactly «Failed to download package files».
I already changed server and cleaned /var/lib/apt/lists/: every time, apt works like a charm, but GUI softwares don't.
I can continue using the command line, but I'd like to understand why this is happening.
Thank you in advance.
EDIT: Synaptic says:
Could not open file /var/cache/apt/archives/partial/libmysqlclient20_5.7.27-0ubuntu0.18.04.1_amd64.deb - open (2: No such file or directory) [IP: 2001:618:1:129::165 80]
This is repeated for every package to download.
If I try to remove the /var/cache/apt/archives directory I get
rm: cannot remove '/var/cache/apt/archives/': Device or resource busy
When I run
sudo apt-get update and
sudo apt-get upgrade I don't get any errors. Updates get installed correctly. That's what I meant by saying that «apt has no problem at all».
UPDATE: I applied some updates with
apt-get forcing IPv4, and everything went smoothly.
update-manager still doesn't work.