[Advcomparch] Πρόβλημα με την εγκατάσταση των libraries

[alexandra]

Καλησπέρα,
όταν εκτελώ την εντολή $ sudo apt-get install libbz2-dev libsqlite3-dev
libboost-dev zlib1g-dev μου βγαίνει το εξής error:

Err:1 http://ppa.launchpad.net/x2go/stable/ubuntu xenial InRelease
  Could not resolve 'ppa.launchpad.net'
Err:2 http://gr.archive.ubuntu.com/ubuntu xenial InRelease

  Could not resolve 'gr.archive.ubuntu.com'
Err:3 http://gr.archive.ubuntu.com/ubuntu xenial-updates InRelease

  Could not resolve 'gr.archive.ubuntu.com'
Err:4 http://gr.archive.ubuntu.com/ubuntu xenial-backports InRelease
  Could not resolve 'gr.archive.ubuntu.com'
Hit:5 http://security.ubuntu.com/ubuntu xenial-security InRelease
Reading package lists... Done
W: Failed to fetch
http://gr.archive.ubuntu.com/ubuntu/dists/xenial/InRelease  Could not
resolve 'gr.archive.ubuntu.com'
W: Failed to fetch
http://gr.archive.ubuntu.com/ubuntu/dists/xenial-updates/InRelease  Could
not resolve 'gr.archive.ubuntu.com'
W: Failed to fetch
http://gr.archive.ubuntu.com/ubuntu/dists/xenial-backports/InRelease  Could
not resolve 'gr.archive.ubuntu.com'
W: Failed to fetch
http://ppa.launchpad.net/x2go/stable/ubuntu/dists/xenial/InRelease  Could
not resolve 'ppa.launchpad.net'
W: Some index files failed to download. They have been ignored, or old ones
used instead.

σε τι οφείλεται αυτό και πώς μπορώ να το διορθώσω;
Ευχαριστώ
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