我知道这非常类似于这个问题和这个，但那里的所有答案对我都不起作用。当尝试安装这些问题中提到的软件包时，apt-get 会抛出以下错误消息：
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.
unity-webapps-service : Depends: webapp-container
E: Unable to correct problems, you have held broken packages.
当我尝试安装那里提到的依赖项时，我发现依赖项越来越多。当我选择“修复损坏的软件包”时，Synaptic 软件包管理器会显示错误消息。我该如何修复此问题？
提前致谢，如果您需要更多信息，请发表评论。
更新：运行apt-cache policy webapp-container unity-webapps-service结果如下：
webapp-container:
Installed: (none)
Candidate: 0.23+14.04.20140428-0ubuntu1
Version table:
0.23+14.04.20140428-0ubuntu1 0
500 http://gb.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
0.23+14.04.20140414-0ubuntu1 0
500 http://gb.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
unity-webapps-service:
Installed: (none)
Candidate: 2.5.0~+14.04.20140409-0ubuntu1
Version table:
2.5.0~+14.04.20140409-0ubuntu1 0
500 http://gb.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
100 /var/lib/dpkg/status
更新2： 版本信息：
LSB Version: core-2.0-amd64:core-2.0-noarch:core-3.0-amd64:core-3.0-noarch:core-3.1-amd64:core-3.1-noarch:core-3.2-amd64:core-3.2-noarch:core-4.0-amd64:core-4.0-noarch:core-4.1-amd64:core-4.1-noarch:security-4.0-amd64:security-4.0-noarch:security-4.1-amd64:security-4.1-noarch
Distributor ID: Ubuntu
Description: Ubuntu 14.04.2 LTS
Release: 14.04
Codename: trusty
更新 3：尝试unity-webapps-service使用 aptitude 而不是 apt-get 进行安装时：
The following NEW packages will be installed:
liboxideqt-qmlplugin{a} liboxideqtcore0{a} liboxideqtquick0{ab}
libqt5feedback5{a} libqt5multimedia5{ab} libqt5organizer5{ab}
libqt5positioning5{ab} libunity-webapps0{a}
qtdeclarative5-dialogs-plugin{ab}
qtdeclarative5-privatewidgets-plugin{ab}
qtdeclarative5-qtfeedback-plugin{a}
qtdeclarative5-ubuntu-ui-extras-browser-plugin{a}
qtdeclarative5-ubuntu-ui-toolkit-plugin{ab} unity-webapps-qml{a}
unity-webapps-service webapp-container{ab} webbrowser-app{ab}
0 packages upgraded, 17 newly installed, 0 to remove and 0 not upgraded.
Need to get 26.6 MB of archives. After unpacking 103 MB will be used.
The following packages have unmet dependencies:
webapp-container : Depends: qtdeclarative-abi-5-2-1 which is a virtual package.
libqt5organizer5 : Depends: qtbase-abi-5-2-1 which is a virtual package.
qtdeclarative5-dialogs-plugin : Depends: qtbase-abi-5-2-1 which is a virtual package.
Depends: qtdeclarative-abi-5-2-1 which is a virtual package.
webbrowser-app : Depends: qtdeclarative-abi-5-2-1 which is a virtual package.
qtdeclarative5-privatewidgets-plugin : Depends: qtbase-abi-5-2-1 which is a virtual package.
libqt5multimedia5 : Depends: qtbase-abi-5-2-1 which is a virtual package.
libqt5positioning5 : Depends: qtbase-abi-5-2-1 which is a virtual package.
liboxideqtquick0 : Depends: qtdeclarative-abi-5-2-1 which is a virtual package.
qtdeclarative5-ubuntu-ui-toolkit-plugin : Depends: qtbase-abi-5-2-1 which is a virtual package.
Depends: qtdeclarative-abi-5-2-1 which is a virtual package.
The following actions will resolve these dependencies:
Keep the following packages at their current version:
1) liboxideqt-qmlplugin [Not Installed]
2) liboxideqtcore0 [Not Installed]
3) liboxideqtquick0 [Not Installed]
4) libqt5feedback5 [Not Installed]
5) libqt5multimedia5 [Not Installed]
6) libqt5organizer5 [Not Installed]
7) libqt5positioning5 [Not Installed]
8) libunity-webapps0 [Not Installed]
9) qtdeclarative5-dialogs-plugin [Not Installed]
10) qtdeclarative5-privatewidgets-plugin [Not Installed]
11) qtdeclarative5-qtfeedback-plugin [Not Installed]
12) qtdeclarative5-ubuntu-ui-extras-browser-plugin [Not Installed]
13) qtdeclarative5-ubuntu-ui-toolkit-plugin [Not Installed]
14) unity-webapps-qml [Not Installed]
15) unity-webapps-service [Not Installed]
16) webapp-container [Not Installed]
17) webbrowser-app [Not Installed]
Accept this solution? [Y/n/q/?]
更新 4：输出sudo apt-get install qtdeclarative-abi-5-2-1：
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package qtdeclarative-abi-5-2-1 is a virtual package provided by:
libqt5qml5 5.2.1-3ubuntu15.1 [Not candidate version]
libqt5qml5 5.2.1-3ubuntu15 [Not candidate version]
E: Package 'qtdeclarative-abi-5-2-1' has no installation candidate
输出sudo apt-get install unity-webapp-container：
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package unity-webapp-container
更新 5：输出apt-cache policy libqt5qml5：
libqt5qml5:
Installed: 5.3.0-3ubuntu13~trusty1
Candidate: 5.3.0-3ubuntu13~trusty1
Version table:
*** 5.3.0-3ubuntu13~trusty1 0
500 http://ppa.launchpad.net/mscore-ubuntu/mscore-stable/ubuntu/ trusty/main amd64 Packages
100 /var/lib/dpkg/status
5.2.1-3ubuntu15.1 0
500 http://gb.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
5.2.1-3ubuntu15 0
500 http://gb.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
输出sudo apt-get install webapp-container：
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.
webapp-container : Depends: qtdeclarative-abi-5-2-1
Depends: unity-webapps-qml but it is not going to be installed
Depends: webbrowser-app (= 0.23+14.04.20140428-0ubuntu1)
E: Unable to correct problems, you have held broken packages.
答案1
我愿意冒险并留下回应。
主要问题似乎是 PPA ppa:mscore-ubuntu/mscore-stable。使用此 PPA，您无法使用所需版本的libqt5qml5
因此，使用以下命令删除 PPA。
sudo ppa-purge ppa:mscore-ubuntu/mscore-stable
在那之后
sudo apt-get install -f
最后
sudo apt-get install unity-webapps-service
哪里有问题？
该命令apt-cache policy libqt5qml5返回以下内容。PPA ppa:mscore-ubuntu/mscore-stable 安装了一个较新的版本 (5.3.0)，libqt5qml5
但qtdeclarative-abi-5-2-1需要精确版本 5.2.1。
libqt5qml5:
Installed: 5.3.0-3ubuntu13~trusty1
Candidate: 5.3.0-3ubuntu13~trusty1
Version table:
*** 5.3.0-3ubuntu13~trusty1 0
500 http://ppa.launchpad.net/mscore-ubuntu/mscore-stable/ubuntu/ trusty/main amd64 Packages
100 /var/lib/dpkg/status
5.2.1-3ubuntu15.1 0
500 http://gb.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
5.2.1-3ubuntu15 0
500 http://gb.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
副作用
清除 PPA 会降级 PPA 安装的软件包。如果由于软件包仅存在于此 PPA 中而无法降级，则将删除该软件包。删除后，软件包的配置文件仍存在于您的系统中。