After that I have follo the instruction reported here:
https://software.opensuse.org/download/package?project=isv:ownCloud:desktop&package=owncloud-client
my Ubuntu16 is not usable.
sudo apt-get install owncloud-client
Reading package lists… Done
Building dependency tree
Reading state information… Done
The following additional packages will be installed:
libowncloudsync0 libxcb-xinerama0 mesa-utils ocqt562-libqt5core5a
ocqt562-libqt5dbus5 ocqt562-libqt5gui5 ocqt562-libqt5keychain1
ocqt562-libqt5network5 ocqt562-libqt5opengl5 ocqt562-libqt5printsupport5
ocqt562-libqt5sql5 ocqt562-libqt5sql5-sqlite ocqt562-libqt5webkit5
ocqt562-libqt5widgets5 ocqt562-libqt5xml5 owncloud-client-l10n
Suggested packages:
ocqt562-libqt5libqgtk2 owncloud-client-dolphin owncloud-client-nautilus
owncloud-client-nemo owncloud-client-caja
Recommended packages:
ocqt562-libqt5svg5
The following NEW packages will be installed:
libowncloudsync0 libxcb-xinerama0 mesa-utils ocqt562-libqt5core5a
ocqt562-libqt5dbus5 ocqt562-libqt5gui5 ocqt562-libqt5keychain1
ocqt562-libqt5network5 ocqt562-libqt5opengl5 ocqt562-libqt5printsupport5
ocqt562-libqt5sql5 ocqt562-libqt5sql5-sqlite ocqt562-libqt5webkit5
ocqt562-libqt5widgets5 ocqt562-libqt5xml5 owncloud-client
owncloud-client-l10n
0 upgraded, 17 newly installed, 0 to remove and 560 not upgraded.
Need to get 18,5 MB of archives.
After this operation, 70,2 MB of additional disk space will be used.
Do you want to continue? [Y/n] Y
WARNING: The following packages cannot be authenticated!
ocqt562-libqt5core5a ocqt562-libqt5dbus5 ocqt562-libqt5network5
ocqt562-libqt5gui5 ocqt562-libqt5widgets5 ocqt562-libqt5opengl5
ocqt562-libqt5printsupport5 ocqt562-libqt5sql5 ocqt562-libqt5webkit5
ocqt562-libqt5keychain1 libowncloudsync0 ocqt562-libqt5sql5-sqlite
ocqt562-libqt5xml5 owncloud-client-l10n owncloud-client
Install these packages without verification? [y/N] Y
Get:1 Index of /ubuntu/ xenial/main amd64 libxcb-xinerama0 amd64 1.11.1-1ubuntu1 [5.204 B]
Get:2 Index of /ubuntu/ xenial/universe amd64 mesa-utils amd64 8.3.0-1 [31,0 kB]
Err:3 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 ocqt562-libqt5core5a 5.6.2-1+22.1
Protocol “http” not supported or disabled in libcurl
Err:4 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 ocqt562-libqt5dbus5 5.6.2-1+22.1
Protocol “http” not supported or disabled in libcurl
Err:5 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 ocqt562-libqt5network5 5.6.2-1+22.1
Protocol “http” not supported or disabled in libcurl
Err:6 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 ocqt562-libqt5gui5 5.6.2-1+22.1
Protocol “http” not supported or disabled in libcurl
Err:7 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 ocqt562-libqt5widgets5 5.6.2-1+22.1
Protocol “http” not supported or disabled in libcurl
Err:8 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 ocqt562-libqt5opengl5 5.6.2-1+22.1
Protocol “http” not supported or disabled in libcurl
Err:9 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 ocqt562-libqt5printsupport5 5.6.2-1+22.1
Protocol “http” not supported or disabled in libcurl
Err:10 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 ocqt562-libqt5sql5 5.6.2-1+22.1
Protocol “http” not supported or disabled in libcurl
Err:11 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 ocqt562-libqt5webkit5 5.6.2-1
Protocol “http” not supported or disabled in libcurl
Err:12 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 ocqt562-libqt5keychain1 0.7.0-1+4.4
Protocol “http” not supported or disabled in libcurl
Err:13 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 libowncloudsync0 2.3.3-8338
Protocol “http” not supported or disabled in libcurl
Err:14 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 ocqt562-libqt5sql5-sqlite 5.6.2-1+22.1
Protocol “http” not supported or disabled in libcurl
Err:15 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 ocqt562-libqt5xml5 5.6.2-1+22.1
Protocol “http” not supported or disabled in libcurl
Err:16 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 owncloud-client-l10n 2.3.3-8338
Protocol “http” not supported or disabled in libcurl
Err:17 https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04 owncloud-client 2.3.3-8338
Protocol “http” not supported or disabled in libcurl
Fetched 36,2 kB in 3s (11,9 kB/s)
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/ocqt562-libqt5core5a_5.6.2-1+22.1_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/ocqt562-libqt5dbus5_5.6.2-1+22.1_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/ocqt562-libqt5network5_5.6.2-1+22.1_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/ocqt562-libqt5gui5_5.6.2-1+22.1_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/ocqt562-libqt5widgets5_5.6.2-1+22.1_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/ocqt562-libqt5opengl5_5.6.2-1+22.1_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/ocqt562-libqt5printsupport5_5.6.2-1+22.1_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/ocqt562-libqt5sql5_5.6.2-1+22.1_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/ocqt562-libqt5webkit5_5.6.2-1_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/ocqt562-libqt5keychain1_0.7.0-1+4.4_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/libowncloudsync0_2.3.3-8338_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/ocqt562-libqt5sql5-sqlite_5.6.2-1+22.1_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/ocqt562-libqt5xml5_5.6.2-1+22.1_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./all/owncloud-client-l10n_2.3.3-8338_all.deb Protocol “http” not supported or disabled in libcurl
E: Failed to fetch https://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Ubuntu_16.04/./amd64/owncloud-client_2.3.3-8338_amd64.deb Protocol “http” not supported or disabled in libcurl
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
best