Errors after doing sudo apt-get update?

Question

ubuntu

Good evening. After executing sudo apt-get update , it started giving errors like this:
W: An error occurred while verifying the signature. The repository has not been updated and the previous index files will be used. GPG Error: ru.archive.ubuntu.com trusty-updates InRelease: Clearsigned file isn't valid, got 'NODATA' (does the network require authentication?)
E: GPG Error: ru.archive.ubuntu.com trusty InRelease: Clearsigned file isn't valid, got 'NODATA' (does the network require authentication?)
There were also problems installing the plugin (xvfb) via the terminal. But after running sudo dpkg --configure -a && sudo apt-get -f install && sudo apt-get update && sudo apt-get dist-upgradestill managed to install it. But the errors after running sudo apt-get update did not disappear.

Answer 1

Read the text of the error. Google what GnuPG is.

Answer 2

ubuntush certificate files are corrupted, try to reinstall manually.
download the package here https://packages.ubuntu.com/zesty/ubuntu-keyring (just choose your distribution correctly, the keys for 16.04lts and younger differ from subsequent versions)
and install the package on the system sudo dpkg -i

Answer 3

Noticed these lines in the error:
Received:2 ru.archive.ubuntu.com trusty InRelease [1491 B]
100% [2 InRelease gpgv 1491 B] [Waiting for headers] [Wai�Splitting up /var/lib/apt /lists/partial/en.archive.ubuntu.com_ubuntu_dists_trusty_InRelease into data Ign ru.archive.ubuntu.com trusty InRelease
W: An error occurred while verifying the signature. The repository has not been updated and the previous index files will be used. GPG error: ru.archive.ubuntu.com trusty-updates InRelease: Clearsigned file isn't valid, got 'NODATA' (does the network require authentication?
)
/var/lib/apt/lists/partial/ru.archive.ubuntu.com_ubuntu_dists_trusty_InRelease
And it contains the following text:
Access blocked by decree of the President of Ukraine No.
133/2017 We dotremuёmosya laws of Ukraine and musheni obmezhite access to this resource.
Could this be the cause of the error? And what to do with this file?
I changed the server for downloading updates in the settings and it all worked.