我的 Ubuntu 发行版 (16.04) 现在认为它是 ElementaryOS。我想尝试 Pantheon 桌面，所以我安装了它，但是现在当我运行 lsb_release -a 时，我得到了以下信息
No LSB modules are available.
Distributor ID: elementary
Description: elementary OS 0.4 Loki
Release: 0.4
Codename: loki
我一直在检查我的 /etc/apt/sources.list，发现缺少“main”，所以我添加了它，但这没有帮助
# deb cdrom:[Ubuntu 15.10 _Wily Werewolf_ - Release amd64 (20151021)]/ wily main restricted
###### Ubuntu Main Repos
deb http://us.archive.ubuntu.com/ubuntu/ xenial main
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://us.archive.ubuntu.com/ubuntu/ xenial restricted main universe
deb-src http://us.archive.ubuntu.com/ubuntu/ xenial restricted main universe
## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ xenial-updates restricted main universe
deb-src http://us.archive.ubuntu.com/ubuntu/ xenial-updates restricted main universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://us.archive.ubuntu.com/ubuntu/ xenial multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ xenial multiverse
deb http://us.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ xenial-backports restricted multiverse main universe
deb-src http://us.archive.ubuntu.com/ubuntu/ xenial-backports restricted multiverse main universe
deb http://security.ubuntu.com/ubuntu xenial-security main
deb http://security.ubuntu.com/ubuntu xenial-security restricted main universe
deb-src http://security.ubuntu.com/ubuntu xenial-security restricted main universe
deb http://security.ubuntu.com/ubuntu xenial-security multiverse
deb-src http://security.ubuntu.com/ubuntu xenial-security multiverse
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu wily partner
# deb-src http://archive.canonical.com/ubuntu wily partner
有想法该怎么解决这个吗？