当出现上述问题时
首先更新系统软件源
sudo apt-get update
sudo apt-get grade
接着再装试一试
sudo apt-get install
如果还不行就要更新软件源

• Ubuntu 更新软件源的方法

1、打开终端；
2、输入命令备份原有软件源文件；
3、打开sources.list文件并添加新的软件源地址；
4、输入命令更新系统软件源地址。

• 具体步骤

具体步骤如下：
1、使用快捷键【ctrl+alt+t】打开终端。
2、输入以下命令备份原有软件源文件。
cp /etc/apt/sources.list /etc/apt/sources.list.bak_yyyymmdd
3、再输入以下命令打开sources.list文件并添加新的软件源地址。
vim /etc/apt/sources.list #打开sources.list文件

PS： 新安装的Ubuntu可能没有安装Vim, 用如下命令先安装Vim：
sudo apt-get install vim-gtk

在文件末尾添加新的软件源地址，常用国内源地址如下：

#阿里源地址

deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse

#华为源地址

deb https://repo.huaweicloud.com/ubuntu/ focal main restricted
deb https://repo.huaweicloud.com/ubuntu/ focal-updates main restricted
deb https://repo.huaweicloud.com/ubuntu/ focal universe
deb https://repo.huaweicloud.com/ubuntu/ focal-updates universe
deb https://repo.huaweicloud.com/ubuntu/ focal-backports main restricted universe
deb https://repo.huaweicloud.com/ubuntu/ focal-security main restricted
deb https://repo.huaweicloud.com/ubuntu/ focal-security universe

#中科大源地址

deb https://mirrors.ustc.edu.cn/ubuntu/ bionic main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse

#163源地址

deb http://mirrors.163.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic-backports main restricted universe multiverse

#清华源地址

deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe ultiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe ultiverse

• apt工作原理

每当执行命令进行软件的安装或着更新，或者软件源的更新时，apt会访问/etc/apt/sources.list内的地址，并在该网站中找到对应系统的包信息例如我的操作系统是ubuntu，网站是deb http://mirrors.163.com/ubuntu/ precise main restricted universe multiverse网易的，那么当我们执行安装的命令时，他就会对应的访问http://mirrors.163.com/ubuntu/dists/lucid/main/binary-i386/的packages.gz，这个文件是服务器上软件包及其依赖关系的清单，并且用gzip压缩过了。apt-get update使用这个清单来确定能够获得哪些补充的软件包且他的内容会被保存在/var/lib/apt/lists内，通过访问这个lists确定该软件是否已安装，是否是最新版本，依赖关系是否满足，从而确定要更新内容，并进行更新，其安装过程主要是由dpkg来完成。

总体上来说apt是倾向于下载的一个管理工具