ошибка аутентификации?

Я получаю это сообщение:

Reading package lists...
Building dependency tree...
Reading state information...
The following packages will be upgraded:
  libcgmanager0
1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 34.2 kB of archives.
After this operation, 33.8 kB of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
  libcgmanager0
E: There are problems and -y was used without --force-yes

Что я могу сделать для фиксации этого?

Редактирование 1:

Когда я делаю sudo apt-key update:

gpg: key 437D05B5: "Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>" not changed
gpg: key FBB75451: "Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>" not changed
gpg: key C0B21F32: "Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>" not changed
gpg: key EFE21092: "Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>" not changed
gpg: Total number processed: 4
gpg: unchanged: 4

Редактирование 2:

Когда я делаю sudo apt-get update:

Err us.archive.ubuntu.com trusty InRelease
Err us.archive.ubuntu.com trusty-updates InRelease
Err us.archive.ubuntu.com trusty-backports InRelease
Err security.ubuntu.com trusty-security InRelease
Err download.webmin.com sarge InRelease
Err security.ubuntu.com trusty-security Release.gpg Could not resolve 'security.ubuntu.com'
Err download.webmin.com sarge Release.gpg Could not resolve 'download.webmin.com'
Err webmin.mirror.somersettechsolutions.co.uk sarge InRelease

Err us.archive.ubuntu.com trusty Release.gpg Could not resolve 'us.archive.ubuntu.com'
Err us.archive.ubuntu.com trusty-updates Release.gpg Could not resolve 'us.archive.ubuntu.com'
Err webmin.mirror.somersettechsolutions.co.uk sarge Release.gpg Could not resolve 'webmin.mirror.somersettechsolutions.co.uk'
Err us.archive.ubuntu.com trusty-backports Release.gpg Could not resolve 'us.archive.ubuntu.com'
Reading package lists... Done

W: Failed to fetch us.archive.ubuntu.com/ubuntu/dists/trusty/InRelease

W: Failed to fetch us.archive.ubuntu.com/ubuntu/dists/trusty-updates/InRelease

W: Failed to fetch us.archive.ubuntu.com/ubuntu/dists/trusty-backports/InRelease

W: Failed to fetch security.ubuntu.com/ubuntu/dists/trusty-security/InRelease

W: Failed to fetch download.webmin.com/download/repository/dists/sarge/InRelease

W: Failed to fetch webmin.mirror.somersettechsolutions.co.uk/repository/dists/…

W: Failed to fetch us.archive.ubuntu.com/ubuntu/dists/trusty/Release.gpg Could not resolve 'us.archive.ubuntu.com'

W: Failed to fetch webmin.mirror.somersettechsolutions.co.uk/repository/dists/… Could not resolve 'webmin.mirror.somersettechsolutions.co.uk'

W: Some index files failed to download. They have been ignored, or old ones used instead.