本人环境：ubuntu18.04 docker中安装opencv的依赖apt install libopencv-dev出现此问题：
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: libopencv-dev : Depends: libopencv-calib3d2.4 but it is not going to be installed Depends: libopencv-features2d2.4 but it is not going to be installed Depends: libopencv-highgui2.4 but it is not going to be installed Depends: libopencv-legacy2.4 but it is not going to be installed Depends: libopencv-objdetect2.4 but it is not going to be installed Depends: libopencv-objdetect-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libopencv-highgui-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libopencv-calib3d-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libopencv-features2d-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libopencv-legacy-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libopencv-contrib-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libopencv-ts-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libopencv-videostab-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libopencv-stitching-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libopencv-superres-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libopencv-ocl-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libopencv2.4-java (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libopencv2.4-jni (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libcv-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libhighgui-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed Depends: libcvaux-dev (= 2.4.9.1+dfsg-1+deb8u1) but it is not going to be installed E: Unable to correct problems, you have held broken packages.原因：刚才服务器下建立的容器，里面的源比较老，搜索不到上述依赖包
解决：打开软件源配置文件
打开后输入
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal main restricted universe multiversedeb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted universe multiversedeb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiversedeb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted universe multiverse保存退出后，利用下述命令更新
sudo apt-get update更新后依赖包正常安装