Linux – apt-get update reports GPG errors

aptdebianlinux

This is what happens when I do apt-get update:

Get:1 http://security.debian.org stretch/updates InRelease [68.2 kB]       
Ign:1 http://security.debian.org stretch/updates InRelease                     
Get:2 http://ftp.bme.hu/debian stretch InRelease [175 kB]
Get:3 http://ftp.cz.debian.org/debian stretch-updates InRelease [88.5 kB]
Ign:2 http://ftp.bme.hu/debian stretch InRelease                  
Ign:3 http://ftp.cz.debian.org/debian stretch-updates InRelease
Fetched 332 kB in 1s (175 kB/s)
Reading package lists... Done
W: GPG error: http://security.debian.org stretch/updates InRelease: At least one invalid signature was encountered.
W: The repository 'http://security.debian.org stretch/updates InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: http://ftp.bme.hu/debian stretch InRelease: At least one invalid signature was encountered.
W: The repository 'http://httpredir.debian.org/debian stretch InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: http://ftp.cz.debian.org/debian stretch-updates InRelease: At least one invalid signature was encountered.
W: The repository 'http://httpredir.debian.org/debian stretch-updates InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.

Here's my sources.list:

deb http://httpredir.debian.org/debian/ stretch main non-free contrib
deb-src http://httpredir.debian.org/debian/ stretch main non-free contrib

deb http://security.debian.org/ stretch/updates main non-free contrib
deb http://httpredir.debian.org/debian/ stretch-updates main non-free contrib

How do I fix this? I've already tried the suggestions from here.

Best Answer

From the comments : The problem is solved by upgrading packages :

sudo apt-get update && sudo apt-get dist-upgrade
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