Package python-software-properties is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source However the following packages replace it: software-properties-common E: Package 'python-software-properties' has no installation candidate

非常抱歉，我之前的回答仍有误。在 Ubuntu 20.04 及其之后的版本中，`python-software-properties` 包已经被废弃了，因此你需要安装 `software-properties-common` 包来代替它。你可以使用以下命令来安装该包：

sudo apt-get update
sudo apt-get install software-properties-common

安装完成后，你可以再次尝试安装 Torch，看看是否能够成功安装了。希望这次能对你有所帮助！

相关问题

Package percona-xtrabackup is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source

如果在安装Percona XtraBackup时出现"Package percona-xtrabackup is not available, but is referred to by another package"的错误，可能是因为您的系统没有正确配置Percona XtraBackup的软件源。

请按照以下步骤进行操作来添加Percona XtraBackup的软件源：

1. 打开终端，使用以下命令下载并添加Percona XtraBackup的软件源密钥：

   wget https://repo.percona.com/apt/percona-release_latest.$(lsb_release -sc)_all.deb
   sudo dpkg -i percona-release_latest.$(lsb_release -sc)_all.deb

2. 更新软件包列表：

   sudo apt-get update

3. 安装Percona XtraBackup：

   sudo apt-get install percona-xtrabackup

这样应该就能够成功安装Percona XtraBackup了。如果仍然遇到问题，请确保您的网络连接正常，并检查您的系统是否与Percona XtraBackup的软件源兼容。

Package qt5-default is not available, but is referred to by another package.

The package `qt5-default` is a metapackage that installs the default Qt 5 development files and dependencies. If you are encountering the error message "Package qt5-default is not available, but is referred to by another package," it means that the package is not available in the package repositories enabled on your system.

To resolve this issue, you can try the following steps:

1. Update the package repositories on your system by running the command:

   sudo apt update

2. Try installing the package again using the following command:

   sudo apt install qt5-default

If the above steps do not resolve the issue, it is possible that the package is not available in the repositories you have enabled. In that case, you may need to check if there are alternative packages or repositories that provide similar functionality or consult the documentation or community for the specific software you are working with.