# apt update 
Get:1 http://deb.debian.org/debian unstable InRelease [161 kB]
Get:2 https://artifacts.elastic.co/packages/7.x/apt stable InRelease [10.4 kB]                                                                                                                  
Err:1 http://deb.debian.org/debian unstable InRelease                                                                                                                                           
  Unknown error executing apt-key
Err:2 https://artifacts.elastic.co/packages/7.x/apt stable InRelease                                                                                                                            
  Unknown error executing apt-key
Get:3 http://ppa.launchpad.net/deadsnakes/ppa/ubuntu bionic InRelease [15.9 kB]                                                                                                                 
Get:4 http://apt.postgresql.org/pub/repos/apt bionic-pgdg InRelease [110 kB]                                                                                              
Err:3 http://ppa.launchpad.net/deadsnakes/ppa/ubuntu bionic InRelease                                                                                               
  Unknown error executing apt-key
Get:5 http://us.archive.ubuntu.com/ubuntu bionic InRelease [242 kB]                                                             
Get:6 http://security.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB]                                    
Err:4 http://apt.postgresql.org/pub/repos/apt bionic-pgdg InRelease                                                        
  Unknown error executing apt-key
Err:6 http://security.ubuntu.com/ubuntu bionic-security InRelease                                                    
  Unknown error executing apt-key
Err:5 http://us.archive.ubuntu.com/ubuntu bionic InRelease                          
  Unknown error executing apt-key
Get:8 http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]
Err:8 http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease
  Unknown error executing apt-key
Get:7 https://repos.citusdata.com/community/ubuntu bionic InRelease [23.2 kB]
Err:7 https://repos.citusdata.com/community/ubuntu bionic InRelease
  Unknown error executing apt-key
Reading package lists... Done
W: GPG error: http://deb.debian.org/debian unstable InRelease: Unknown error executing apt-key
E: The repository 'http://deb.debian.org/debian unstable 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: https://artifacts.elastic.co/packages/7.x/apt stable InRelease: Unknown error executing apt-key
E: The repository 'https://artifacts.elastic.co/packages/7.x/apt stable 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://ppa.launchpad.net/deadsnakes/ppa/ubuntu bionic InRelease: Unknown error executing apt-key
E: The repository 'http://ppa.launchpad.net/deadsnakes/ppa/ubuntu bionic 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://apt.postgresql.org/pub/repos/apt bionic-pgdg InRelease: Unknown error executing apt-key
E: The repository 'http://apt.postgresql.org/pub/repos/apt bionic-pgdg 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://security.ubuntu.com/ubuntu bionic-security InRelease: Unknown error executing apt-key
E: The repository 'http://security.ubuntu.com/ubuntu bionic-security 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://us.archive.ubuntu.com/ubuntu bionic InRelease: Unknown error executing apt-key
E: The repository 'http://us.archive.ubuntu.com/ubuntu bionic 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://us.archive.ubuntu.com/ubuntu bionic-updates InRelease: Unknown error executing apt-key
E: The repository 'http://us.archive.ubuntu.com/ubuntu bionic-updates 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: https://repos.citusdata.com/community/ubuntu bionic InRelease: Unknown error executing apt-key
E: The repository 'https://repos.citusdata.com/community/ubuntu bionic 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.


My All servers are on AWS and facing same issue in multiple servers.unable to update server.I have spent manny days on troubleshooting this issue.but did not find solution.

but at Last i got this command 

echo 'APT::Sandbox::User "root";' >/etc/apt/apt.conf.d/00temp
it works and now i can update repository.

Q.1 Why i have to run this command ? anyone know exact reason behind this.
Q.2 Is this a type of security hole ?

FYI @David Kalnischkies @mila nuts