failed to fetch security undermined error [IP: 91.189.91.38 80] in ubuntu 20.04

upgrade apt updates 20.04

First i did sudo apt update and sudo apt-get update worked fine but after doing sudo apt upgrade and sudo apt-get upgrade getting below error

     sudo apt upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
The following NEW packages will be installed:
  linux-headers-5.4.0-59 linux-headers-5.4.0-59-generic linux-image-5.4.0-59-generic linux-modules-5.4.0-59-generic linux-modules-extra-5.4.0-59-generic
The following packages will be upgraded:
  libasound2 libasound2-data libatopology2 libproxy1-plugin-gsettings libproxy1-plugin-networkmanager libproxy1v5 linux-generic-hwe-20.04 linux-headers-generic-hwe-20.04
  linux-image-generic-hwe-20.04 linux-libc-dev nautilus-sendto python-apt-common python3-apt
13 upgraded, 5 newly installed, 0 to remove and 0 not upgraded.
Need to get 72.5 kB/76.0 MB of archives.
After this operation, 360 MB of additional disk space will be used.
Do you want to continue? [Y/n] Y
Get:1 http://in.archive.ubuntu.com/ubuntu focal-updates/main amd64 libproxy1-plugin-networkmanager amd64 0.4.15-10ubuntu1.2 [5,284 B]
Ign:1 http://in.archive.ubuntu.com/ubuntu focal-updates/main amd64 libproxy1-plugin-networkmanager amd64 0.4.15-10ubuntu1.2
Get:2 http://in.archive.ubuntu.com/ubuntu focal-updates/main amd64 libproxy1-plugin-gsettings amd64 0.4.15-10ubuntu1.2 [18.1 kB]
Ign:2 http://in.archive.ubuntu.com/ubuntu focal-updates/main amd64 libproxy1-plugin-gsettings amd64 0.4.15-10ubuntu1.2
Get:3 http://in.archive.ubuntu.com/ubuntu focal-updates/main amd64 libproxy1v5 amd64 0.4.15-10ubuntu1.2 [49.1 kB]
Ign:3 http://in.archive.ubuntu.com/ubuntu focal-updates/main amd64 libproxy1v5 amd64 0.4.15-10ubuntu1.2
Get:1 http://security.ubuntu.com/ubuntu focal-updates/main amd64 libproxy1-plugin-networkmanager amd64 0.4.15-10ubuntu1.2 [5,284 B]
Err:1 http://security.ubuntu.com/ubuntu focal-updates/main amd64 libproxy1-plugin-networkmanager amd64 0.4.15-10ubuntu1.2
  Undetermined Error [IP: 91.189.88.152 80]
Get:2 http://security.ubuntu.com/ubuntu focal-updates/main amd64 libproxy1-plugin-gsettings amd64 0.4.15-10ubuntu1.2 [18.1 kB]
Err:2 http://security.ubuntu.com/ubuntu focal-updates/main amd64 libproxy1-plugin-gsettings amd64 0.4.15-10ubuntu1.2
  Undetermined Error [IP: 91.189.88.152 80]
Get:3 http://security.ubuntu.com/ubuntu focal-updates/main amd64 libproxy1v5 amd64 0.4.15-10ubuntu1.2 [49.1 kB]
Err:3 http://security.ubuntu.com/ubuntu focal-updates/main amd64 libproxy1v5 amd64 0.4.15-10ubuntu1.2
  Undetermined Error [IP: 91.189.88.152 80]
E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/libp/libproxy/libproxy1-plugin-networkmanager_0.4.15-10ubuntu1.2_amd64.deb  Undetermined Error [IP: 91.189.88.152 80]
E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/libp/libproxy/libproxy1-plugin-gsettings_0.4.15-10ubuntu1.2_amd64.deb  Undetermined Error [IP: 91.189.88.152 80]
E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/libp/libproxy/libproxy1v5_0.4.15-10ubuntu1.2_amd64.deb  Undetermined Error [IP: 91.189.88.152 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

output of

cat /etc/apt/sources.list
# deb cdrom:[Ubuntu 20.04.1 LTS _Focal Fossa_ - Release amd64 (20200731)]/ focal main restricted

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://in.archive.ubuntu.com/ubuntu/ focal main restricted
# deb-src http://in.archive.ubuntu.com/ubuntu/ focal main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://in.archive.ubuntu.com/ubuntu/ focal-updates main restricted
# deb-src http://in.archive.ubuntu.com/ubuntu/ focal-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://in.archive.ubuntu.com/ubuntu/ focal universe
# deb-src http://in.archive.ubuntu.com/ubuntu/ focal universe
deb http://in.archive.ubuntu.com/ubuntu/ focal-updates universe
# deb-src http://in.archive.ubuntu.com/ubuntu/ focal-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://in.archive.ubuntu.com/ubuntu/ focal multiverse
# deb-src http://in.archive.ubuntu.com/ubuntu/ focal multiverse
deb http://in.archive.ubuntu.com/ubuntu/ focal-updates multiverse
# deb-src http://in.archive.ubuntu.com/ubuntu/ focal-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://in.archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
# deb-src http://in.archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu focal partner
# deb-src http://archive.canonical.com/ubuntu focal partner

deb http://security.ubuntu.com/ubuntu focal-security main restricted
# deb-src http://security.ubuntu.com/ubuntu focal-security main restricted
deb http://security.ubuntu.com/ubuntu focal-security universe
# deb-src http://security.ubuntu.com/ubuntu focal-security universe
deb http://security.ubuntu.com/ubuntu focal-security multiverse
# deb-src http://security.ubuntu.com/ubuntu focal-security multiverse

# This system was installed using small removable media
# (e.g. netinst, live or single CD). The matching "deb cdrom"
# entries were disabled at the end of the installation process.
# For information about how to configure apt package sources,
# see the sources.list(5) manual.

sudo apt update --fix-missing

sudo apt update --fix-missing
Hit:1 http://archive.ubuntu.com/ubuntu focal InRelease
Hit:2 http://security.ubuntu.com/ubuntu focal-security InRelease
Hit:3 http://archive.ubuntu.com/ubuntu focal-updates InRelease
Reading package lists... Done
Building dependency tree       
Reading state information... Done
13 packages can be upgraded. Run 'apt list --upgradable' to see them.

sudo apt upgrade
sudo apt upgrade
    Reading package lists... Done
    Building dependency tree       
    Reading state information... Done
    Calculating upgrade... Done
    The following NEW packages will be installed:
      linux-headers-5.4.0-59 linux-headers-5.4.0-59-generic linux-image-5.4.0-59-generic linux-modules-5.4.0-59-generic linux-modules-extra-5.4.0-59-generic
    The following packages will be upgraded:
      libasound2 libasound2-data libatopology2 libproxy1-plugin-gsettings libproxy1-plugin-networkmanager libproxy1v5 linux-generic-hwe-20.04 linux-headers-generic-hwe-20.04
      linux-image-generic-hwe-20.04 linux-libc-dev nautilus-sendto python-apt-common python3-apt
    13 upgraded, 5 newly installed, 0 to remove and 0 not upgraded.
    Need to get 72.5 kB/76.0 MB of archives.
    After this operation, 360 MB of additional disk space will be used.
    Do you want to continue? [Y/n] Y
    Get:1 http://security.ubuntu.com/ubuntu focal-security/main amd64 libproxy1-plugin-networkmanager amd64 0.4.15-10ubuntu1.2 [5,284 B]
    Ign:1 http://security.ubuntu.com/ubuntu focal-security/main amd64 libproxy1-plugin-networkmanager amd64 0.4.15-10ubuntu1.2
    Get:2 http://security.ubuntu.com/ubuntu focal-security/main amd64 libproxy1-plugin-gsettings amd64 0.4.15-10ubuntu1.2 [18.1 kB]
    Ign:2 http://security.ubuntu.com/ubuntu focal-security/main amd64 libproxy1-plugin-gsettings amd64 0.4.15-10ubuntu1.2
    Get:3 http://security.ubuntu.com/ubuntu focal-security/main amd64 libproxy1v5 amd64 0.4.15-10ubuntu1.2 [49.1 kB]
    Ign:3 http://security.ubuntu.com/ubuntu focal-security/main amd64 libproxy1v5 amd64 0.4.15-10ubuntu1.2
    Get:1 http://archive.ubuntu.com/ubuntu focal-security/main amd64 libproxy1-plugin-networkmanager amd64 0.4.15-10ubuntu1.2 [5,284 B]
    Err:1 http://archive.ubuntu.com/ubuntu focal-security/main amd64 libproxy1-plugin-networkmanager amd64 0.4.15-10ubuntu1.2
      Undetermined Error [IP: 91.189.88.142 80]
    Get:2 http://archive.ubuntu.com/ubuntu focal-security/main amd64 libproxy1-plugin-gsettings amd64 0.4.15-10ubuntu1.2 [18.1 kB]
    Err:2 http://archive.ubuntu.com/ubuntu focal-security/main amd64 libproxy1-plugin-gsettings amd64 0.4.15-10ubuntu1.2
      Undetermined Error [IP: 91.189.88.142 80]
    Get:3 http://archive.ubuntu.com/ubuntu focal-security/main amd64 libproxy1v5 amd64 0.4.15-10ubuntu1.2 [49.1 kB]
    Err:3 http://archive.ubuntu.com/ubuntu focal-security/main amd64 libproxy1v5 amd64 0.4.15-10ubuntu1.2
      Undetermined Error [IP: 91.189.88.142 80]
    E: Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/libp/libproxy/libproxy1-plugin-networkmanager_0.4.15-10ubuntu1.2_amd64.deb  Undetermined Error [IP: 91.189.88.142 80]
    E: Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/libp/libproxy/libproxy1-plugin-gsettings_0.4.15-10ubuntu1.2_amd64.deb  Undetermined Error [IP: 91.189.88.142 80]
    E: Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/libp/libproxy/libproxy1v5_0.4.15-10ubuntu1.2_amd64.deb  Undetermined Error [IP: 91.189.88.142 80]
    E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

Revert your repositories list to the original Ubuntu Focal list by running the following command in the terminal:

sudo nano /etc/apt/sources.list

A file editor will be opened. Delete all the lines in it and then copy and paste the following in the file editor:

deb http://archive.ubuntu.com/ubuntu focal main universe multiverse restricted
deb http://security.ubuntu.com/ubuntu/ focal-security main multiverse universe restricted
deb http://archive.ubuntu.com/ubuntu focal-updates main multiverse universe restricted

Then, save and close the file by pressing Ctrl + X then press Y then press Enter

To verify you saved the file correctly, please run the following command in the terminal:

cat /etc/apt/sources.list

The output should be exactly:

deb http://archive.ubuntu.com/ubuntu focal main universe multiverse restricted
deb http://security.ubuntu.com/ubuntu/ focal-security main multiverse universe restricted
deb http://archive.ubuntu.com/ubuntu focal-updates main multiverse universe restricted

Ubuntu repositories have a defined format. They should be for example something like deb http://archive.ubuntu.com/ubuntu bionic main.

Explanation:

deb: These repositories contain binaries or precompiled packages. These repositories are required for most users.

http://archive.ubuntu.com/ubuntu: The URI (Uniform Resource Identifier), in this case a location on the internet.

focal: is the release name of your Ubuntu installation.

main & restricted ...etc: are the section names or components. There can be several section names, separated by spaces.

After that, please clear apt cache by running the following command in the terminal:

sudo apt clean && sudo apt autoclean

Then update your repositories list by running the following command in the terminal:

sudo apt update

You should now be able to install packages and update your system again.

If after that, you still get errors, please first back up /etc/apt/sources.list.d/ to your home directory by running the following command in the terminal:

mkdir ~/old_sources_list_d && sudo cp -r /etc/apt/sources.list.d/* ~/old_sources_list_d/

After that, please clear all existing PPAs and repository lists in /etc/apt/sources.list.d/ by running the following command in the terminal:

sudo rm -r /etc/apt/sources.list.d/*

After that, please clear apt cache by running the following command in the terminal:

sudo apt clean && sudo apt autoclean

Then, please update your repositories list by running the following command again in the terminal:

sudo apt update

Notice:

  • Check if your connection to the Internet is behind a firewall, limited in any way or behind a proxy and configure your system and connection accordingly or change to a different connection if available. Firewalls can block access to certain URLs and proxies can keep old stale links in their cache system and this would result in broken or unresponsive targets. Proxies can also modify the headers of the HTTP requests and interfere with responses from web-servers and change them and your computer might end up getting faulty responses that APT can not handle correctly. This is common in networks that are used by large number of people and limited resources or Internet speed for availability and security reasons.

  • Check if there is an APT proxy configuration file by running the following command:

ls /etc/apt/apt.conf.d/*proxy*

If the command returns back any results, move these files out of the /etc/apt/apt.conf.d/ directory or delete them.

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