Thses errors occurs when i execute apt-get update.

GPG error: http://old-releases.ubuntu.com/ubuntu raring Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32 W: The repository 'http://old-releases.ubuntu.com/ubuntu raring Release' 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.

  • This is probably because Raring Release is end-of-life. What research have you done regarding this error? – music2myear Jun 27 '17 at 17:42

you have manually added some external (unofficial) repositories that will prevent you from updating the packages list

edit /etc/apt/sources.list or any other file in the /etc/apt/sources.list.d/ folder and remove any reference to http://old-releases.ubuntu.com/ubuntu from them

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