Unable to load shared library 'OpenCvSharpExtern' or one of its dependencies. In order to help diagnose loading problems, consider setting the LD_DEBUG environment variable

在ubuntu（18.04）运行OpenCvSharp4（4.6.0）报错如下：

Microsoft.AspNetCore.Server.Kestrel[13]
      Connection id "0HMJAMSQJ3RO8", Request id "0HMJAMSQJ3RO8:00000005": An unhandled exception was thrown by the application.
      System.TypeInitializationException: The type initializer for 'OpenCvSharp.Internal.NativeMethods' threw an exception.
       ---> System.DllNotFoundException: Unable to load shared library 'OpenCvSharpExtern' or one of its dependencies. In order to help diagnose loading problems, consider setting the LD_DEBUG environment variable: libOpenCvSharpExtern: cannot open shared object file: No such file or directory
         at OpenCvSharp.Internal.NativeMethods.redirectError(CvErrorCallback errCallback, IntPtr userdata, IntPtr& prevUserdata)
         at OpenCvSharp.Internal.ExceptionHandler.RegisterExceptionCallback()
         at OpenCvSharp.Internal.NativeMethods.LoadLibraries(IEnumerable`1 additionalPaths)
         at OpenCvSharp.Internal.NativeMethods..cctor()
        ......

在程序根目录shell执行`ldd libOpenCvSharpExtern.so`，查看是否有存在`libOpenCvSharpExtern.so`文件，若显示各种依赖则存在。若不存在，需要copy到程序根目录。

执行`ldd libOpenCvSharpExtern.so`后如下：

root@filescan-5d79f649fc-xqrt9:/app# ldd libOpenCvSharpExtern.so
        linux-vdso.so.1 (0x00007ffda5b3b000)
        libtesseract.so.4 => not found
        libgtk-x11-2.0.so.0 => not found
        libgdk-x11-2.0.so.0 => not found
        libcairo.so.2 => not found
        libgdk_pixbuf-2.0.so.0 => not found
        libgobject-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0 (0x00007fccca620000)
        libglib-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007fccca309000)
        libdc1394.so.22 => not found
        libavcodec.so.57 => not found
        libavformat.so.57 => not found
        libavutil.so.55 => not found
        libswscale.so.4 => not found
        libjpeg.so.8 => not found
        libpng16.so.16 => /usr/lib/x86_64-linux-gnu/libpng16.so.16 (0x00007fccca0d7000)
        libtiff.so.5 => not found
        libIlmImf-2_2.so.22 => not found
        libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007fccc9eba000)
        libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fccc9cb6000)
        libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fccc9a97000)
        librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007fccc988f000)
        libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007fccc9506000)
        libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fccc9168000)
        libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fccc8f50000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fccc8b5f000)
        /lib64/ld-linux-x86-64.so.2 (0x00007fccce7d5000)
        libffi.so.6 => /usr/lib/x86_64-linux-gnu/libffi.so.6 (0x00007fccc8957000)
        libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007fccc86e6000)

可以看出有部分依赖的显示`not found`，需要额外去安装，知道全部依赖都查找得到既解决。

方法：
1、在docker hub找别人配置好环境的镜像（可能存在少量未找到，自行安装既可）
2、可参考如下

RUN apt-get update && apt-get install -y \
    apt-utils \
    libgdiplus \
    libc6-dev \
    libgtk2.0-dev \
    libtbb-dev \
    libatlas-base-dev \
    libvorbis-dev \
    libxvidcore-dev \
    libopencore-amrnb-dev \
    libopencore-amrwb-dev \
    libavresample-dev \
    x264 \
    v4l-utils \
    libwebp-dev \
    tesseract-ocr \
    libtesseract-dev \
    libleptonica-dev \
    libtiff-dev \
    libavcodec-dev \
    libavformat-dev \
    libswscale-dev \
    libdc1394-22-dev \
    libxine2-dev \
    libv4l-dev \
    tesseract-ocr

我最终的环境配置是：

FROM husty530/opencvsharp-ubuntu-1804:latest
ARG DEBIAN_FRONTEND=noninteractive
ENV TZ=Asia/Shanghai

RUN apt update

RUN apt install libgtk2.0-dev tesseract-ocr -y 
RUN wget https://packages.microsoft.com/config/ubuntu/18.04/packages-microsoft-prod.deb -O packages-microsoft-prod.deb
RUN dpkg -i packages-microsoft-prod.deb
RUN rm packages-microsoft-prod.deb

RUN apt-get update
RUN apt-get install -y apt-transport-https
RUN apt-get update
RUN apt-get install -y aspnetcore-runtime-6.0