Here's the issue :
atlas@atlas-Aspire-M5620:~$ export LC_ALL=C
atlas@atlas-Aspire-M5620:~$ sudo apt-get update
[sudo] password for atlas:
Get:1
http://packages.linuxmint.com tricia InRelease [2647 B]
Err:1
http://packages.linuxmint.com tricia InRelease
Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Get:2
http://security.ubuntu.com/ubuntu bionic-security InRelease [2647 B]
Err:2
http://security.ubuntu.com/ubuntu bionic-security InRelease
Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Get:3
http://archive.canonical.com/ubuntu bionic InRelease [2647 B]
Err:3
http://archive.canonical.com/ubuntu bionic InRelease
Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Get:4
http://archive.ubuntu.com/ubuntu bionic InRelease [2647 B]
Err:4
http://archive.ubuntu.com/ubuntu bionic InRelease
Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Get:5
http://archive.ubuntu.com/ubuntu bionic-updates InRelease [2647 B]
Err:5
http://archive.ubuntu.com/ubuntu bionic-updates InRelease
Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Get:6
http://archive.ubuntu.com/ubuntu bionic-backports InRelease [2647 B]
Err:6
http://archive.ubuntu.com/ubuntu bionic-backports InRelease
Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
Reading package lists... Done
N: See apt-secure(8) manpage for repository creation and user configuration details.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
E: The repository 'http://packages.linuxmint.com tricia InRelease' is not signed.
E: Failed to fetch
http://packages.linuxmint.com/dists/tricia/InRelease Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
N: See apt-secure(8) manpage for repository creation and user configuration details.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
E: The repository 'http://security.ubuntu.com/ubuntu bionic-security InRelease' is not signed.
E: Failed to fetch
http://security.ubuntu.com/ubuntu/dists ... /InRelease Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
N: See apt-secure(8) manpage for repository creation and user configuration details.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
E: The repository 'http://archive.canonical.com/ubuntu bionic InRelease' is not signed.
E: Failed to fetch
http://archive.canonical.com/ubuntu/dis ... /InRelease Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
N: See apt-secure(8) manpage for repository creation and user configuration details.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
E: The repository 'http://archive.ubuntu.com/ubuntu bionic InRelease' is not signed.
E: Failed to fetch
http://archive.ubuntu.com/ubuntu/dists/bionic/InRelease Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
E: Failed to fetch
http://archive.ubuntu.com/ubuntu/dists/ ... /InRelease Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
E: The repository 'http://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.
E: Failed to fetch
http://archive.ubuntu.com/ubuntu/dists/ ... /InRelease Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
E: The repository 'http://archive.ubuntu.com/ubuntu bionic-backports 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.
Now that i know that my Linux Mint distribution got something wrong on trying to Update; Question; can you help me with (source.list , PPA's and also set "proxy" or "VPN". Lot of work to do so that's why I am asking for patience . Thank you in advance.