Reading package lists…
W: GPG error: http://apt.postgresql.org/pub/repos/apt trusty-pgdg InRelease: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 7FCC7D46ACCC4CF8
W: The repository ‘http://apt.postgresql.org/pub/repos/apt trusty-pgdg InRelease’ is not signed.
E: Failed to fetch mirror://mirrors.ubuntu.com/mirrors.txt/dists/trusty-updates/main/binary-amd64/Packages.gz Hash Sum mismatch
E: Failed to fetch mirror://mirrors.ubuntu.com/mirrors.txt/dists/trusty-updates/universe/binary-amd64/Packages.gz
E: Some index files failed to download. They have been ignored, or old ones used instead.
How to fix it???