GPG invalid signature error while running apt update inside arm32v7/ubuntu:20.04 docker

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I am trying to upgrade from ubuntu16 to ubuntu20 and for that I need to change image arm32v7/ubuntu:16.04 to arm32v7/ubuntu:20.04 in all our Dockerfiles [update required libraries after that], But while working on this task I found that there's some issue with arm32v7 base image of ubuntu:20.04 - when I run apt-get update it fails with following error messages-

Err:1 http://ports.ubuntu.com/ubuntu-ports focal InRelease
  At least one invalid signature was encountered.
Get:4 http://ports.ubuntu.com/ubuntu-ports focal-security InRelease [107 kB]
Err:2 http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease
  At least one invalid signature was encountered.
Err:3 http://ports.ubuntu.com/ubuntu-ports focal-backports InRelease
  At least one invalid signature was encountered.
Err:4 http://ports.ubuntu.com/ubuntu-ports focal-security InRelease
  At least one invalid signature was encountered.
Reading package lists... Done
W: GPG error: http://ports.ubuntu.com/ubuntu-ports focal InRelease: At least one invalid signature was encountered.
E: The repository 'http://ports.ubuntu.com/ubuntu-ports focal InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease: At least one invalid signature was encountered.
E: The repository 'http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.

I tried the solution mentioned here [https://askubuntu.com/a/1264921/872700] but that too is not working as we are using the image in Dockerfile and its not allowed to pass --security-opt in docker build command.

As a workaround I ran docker run with --security-opt option and created another image with docker commit - then ran apt-get update inside new image but that too is not working.

FYI, The machine has following docker version on it- Docker version 19.03.13, build 4484c46

ubuntu-20.04 dockerfile docker
2 Answers

I had this issue on Docker Desktop for Mac recently, running apt-get update in an Ubuntu 20.04 x86_64 container. It turned out the VM hosting the Docker images on macOS had run out of disk space. That somehow manifested itself as apt reporting invalid signatures on package index files. Pruning unused images to free space solved the issue for me:

docker image prune -a

As mentioned in comment by sema, if the issue is caused by insufficient disk space, another workaround is to increase the size of the virtual disk used by the virtual machine that is running docker. In Docker Desktop for Mac this can be done via Preferences > Resources > Disk image size.

user_138341350

To solve the problem, I had to update the library libseccomp2 on my host pi machine as I could not find any other solution to apply inside the base image.

Downloaded the deb package from here and applied on host machine using -

sudo dpkg -i libseccomp2_2.4.4-1+b1_armhf.deb

user_77457250
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