PGP key error

[researcher123]

I want to upgrade my system from behind a firewall when I got the following error

PGP error: http://deb.opera.com stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F9A2F76A9D1A0061Failed to fetch http://deb.opera.com/opera/dists/stable/non-free/source/Sources.gz 404 Not Found Some index files failed to download, they have been ignored, or old ones used instead."

Please help.

[sikander3786]

Either add the missing Opera key by,


wget -O - http://deb.opera.com/archive.key | sudo apt-key add -


If that doesn't help, edit your sources.list by,


gksudo gedit /etc/apt/sources.list

And put a # at the beginning of Opera line. Save and close and try update/upgrade again.