我刚刚将 Ubuntu 从 18.04 升级到 20.04。
现在我失去了对 NAS 的访问权限，我正在尝试重新安装它。
我阅读了几篇关于其他人在升级时遇到的问题的帖子，包括新的 Samba 不支持 SMB V 1.0 以及如何修复它。
我发现我的系统上没有安装 Samba 客户端，因此我尝试使用以下命令再次安装它：
sudo apt install samba smbclient
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies.
samba : Depends: python3-samba but it is not going to be installed
Depends: samba-common-bin (= 2:4.11.6+dfsg-0ubuntu1.5) but it is not going to be installed
Depends: libldb2 (>= 2:2.0.10~) but it is not going to be installed
Depends: libpython3.8 (>= 3.8.2) but it is not going to be installed
Depends: libwbclient0 (= 2:4.11.6+dfsg-0ubuntu1.5) but 2:4.7.6+dfsg~ubuntu-0ubuntu2.20 is to be installed
Depends: samba-libs (= 2:4.11.6+dfsg-0ubuntu1.5) but 2:4.7.6+dfsg~ubuntu-0ubuntu2.20 is to be installed
Recommends: samba-dsdb-modules but it is not going to be installed
Recommends: samba-vfs-modules but it is not going to be installed
smbclient : Depends: samba-libs (= 2:4.11.6+dfsg-0ubuntu1.5) but 2:4.7.6+dfsg~ubuntu-0ubuntu2.20 is to be installed
Depends: libwbclient0 (= 2:4.11.6+dfsg-0ubuntu1.5) but 2:4.7.6+dfsg~ubuntu-0ubuntu2.20 is to be installed
E: Unable to correct problems, you have held broken packages.
我应该怎么办？
我该如何解决这个问题？
更新1
经过一番搜索，我发现了一些建议更改的帖子/etc/apt/source.list。
我查看了这个文件，我有这个：
# deb cdrom:[Ubuntu 16.04.2 LTS _Xenial Xerus_ - Release amd64 (20170215.2)]/ xenial main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://gb.archive.ubuntu.com/ubuntu/ focal main restricted
# deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://gb.archive.ubuntu.com/ubuntu/ focal-updates main restricted
# deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
## 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.
deb http://gb.archive.ubuntu.com/ubuntu/ focal universe
# deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial universe
deb http://gb.archive.ubuntu.com/ubuntu/ focal-updates universe
# deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial-updates universe
## 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://gb.archive.ubuntu.com/ubuntu/ focal multiverse
# deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial multiverse
deb http://gb.archive.ubuntu.com/ubuntu/ focal-updates multiverse
# deb-src http://gb.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://gb.archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
# deb-src http://gb.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe 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 xenial partner
# deb-src http://archive.canonical.com/ubuntu xenial partner
deb http://security.ubuntu.com/ubuntu focal-security main restricted
# deb-src http://security.ubuntu.com/ubuntu xenial-security main restricted
deb http://security.ubuntu.com/ubuntu focal-security universe
# deb-src http://security.ubuntu.com/ubuntu xenial-security universe
deb http://security.ubuntu.com/ubuntu focal-security multiverse
# deb-src http://security.ubuntu.com/ubuntu xenial-security multiverse
# deb [arch=amd64] https://packages.microsoft.com/repos/vscode stable main # disabled on upgrade to focal
# deb-src [arch=amd64] https://packages.microsoft.com/repos/vscode stable main
这似乎与旧版本的 Ubuntu 有关。这是正确的来源列表吗？我如何确定它指向与 Ubuntu 20.04 相关的软件包？