fallo en la red: depuración de la red muy bien
root@ubuntu:/usr/bin# do-release-upgrade
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [819 B]
Err Upgrade tool
404 Not Found
Fetched 819 B in 0s (0 B/s)
WARNING:root:file 'xenial.tar.gz' missing
Failed to fetch
Fetching the upgrade failed. There may be a network problem.
root@ubuntu:/usr/bin# ping www.baidu.com
PING www.a.shifen.com (182.61.200.7) 56(84) bytes of data.
