Paket software-properties-common kann nicht gefunden werden [geschlossen]

auf meinem 15.04 ubuntu (ich habe es als virtuellen server bekommen) möchte ich unity installieren ... aber schritt für schritt so faust software-properties-common, aber ich habe:

 sudo apt-get install software-properties-common
Reading package lists... Done
Building dependency tree... Done
E: Unable to locate package software-properties-common

Kann jemand helfen, wie es weitergeht?

/# cat /etc/apt/sources.list
deb http://archive.ubuntu.com/ubuntu vivid main restricted universe
deb http://archive.ubuntu.com/ubuntu vivid-updates main restricted universe
deb http://security.ubuntu.com/ubuntu vivid-security main restricted universe multiverse
deb http://archive.canonical.com/ubuntu vivid partner

/# sudo apt-get update
Get:1 http://security.ubuntu.com vivid-security InRelease [64.4 kB]
Get:2 http://archive.ubuntu.com vivid InRelease [218 kB]
Get:3 http://archive.canonical.com vivid InRelease [10.3 kB]
Get:4 http://archive.canonical.com vivid/partner amd64 Packages [2978 B]
Get:5 http://security.ubuntu.com vivid-security/main amd64 Packages [166 kB]
Ign http://archive.canonical.com vivid/partner Translation-en
Get:6 http://security.ubuntu.com vivid-security/restricted amd64 Packages [11.2 kB]
Get:7 http://archive.ubuntu.com vivid-updates InRelease [64.4 kB]
Get:8 http://security.ubuntu.com vivid-security/universe amd64 Packages [66.3 kB]
Get:9 http://archive.ubuntu.com vivid/main amd64 Packages [1364 kB]
Get:10 http://security.ubuntu.com vivid-security/multiverse amd64 Packages [6045 B]
Get:11 http://security.ubuntu.com vivid-security/main Translation-en [79.8 kB]
Get:12 http://security.ubuntu.com vivid-security/multiverse Translation-en [2743 B]
Get:13 http://security.ubuntu.com vivid-security/restricted Translation-en [2774 B]
Get:14 http://security.ubuntu.com vivid-security/universe Translation-en [41.2 kB]
Get:15 http://archive.ubuntu.com vivid/restricted amd64 Packages [15.4 kB]
Get:16 http://archive.ubuntu.com vivid/universe amd64 Packages [6485 kB]
Get:17 http://archive.ubuntu.com vivid/main Translation-en [793 kB]
Get:18 http://archive.ubuntu.com vivid/restricted Translation-en [4228 B]
Get:19 http://archive.ubuntu.com vivid/universe Translation-en [4456 kB]
Get:20 http://archive.ubuntu.com vivid-updates/main amd64 Packages [260 kB]
Get:21 http://archive.ubuntu.com vivid-updates/restricted amd64 Packages [13.6 kB]
Get:22 http://archive.ubuntu.com vivid-updates/universe amd64 Packages [127 kB]
Get:23 http://archive.ubuntu.com vivid-updates/main Translation-en [125 kB]
Get:24 http://archive.ubuntu.com vivid-updates/restricted Translation-en [3112 B]
Get:25 http://archive.ubuntu.com vivid-updates/universe Translation-en [74.6 kB]
Fetched 14.5 MB in 28s (506 kB/s)
Reading package lists... Done

Danach sudo apt-get updatekonnte ich installieren software-properties-common.