ubuntu20.04安装opencv4.2 cmake报错

ubuntu20.04安装opencv4.2 cmake报错
参考：https://blog.youkuaiyun.com/qq_34256375/article/details/107836051
https://docs.opencv.org/4.2.0/d7/d9f/tutorial_linux_install.html
https://blog.youkuaiyun.com/u011622208/article/details/104265206
备注：安装过程尽量看看官方文档

$ cmake -D OPENCV_EXTRA_MODULES_PATH=~/opencv_contrib/modules CMAKE_C_COMPILER=/usr/bin/gcc-5 ..

然后

-- Detected processor: x86_64
-- Looking for ccache - not found
-- Found ZLIB: /usr/lib/x86_64-linux-gnu/libz.so (found suitable version "1.2.11", minimum required is "1.2.3") 
-- Found ZLIB: /usr/lib/x86_64-linux-gnu/libz.so (found version "1.2.11") 
-- IPPICV: Download: ippicv_2019_lnx_intel64_general_20180723.tgz
-- Try 1 failed
-- 
=======================================================================
  Couldn't connect to server from the Internet.
  Perhaps direct connections are not allowed in the current network.
  To use proxy please check/specify these environment variables:
  - http_proxy/https_proxy
  - and/or HTTP_PROXY/HTTPS_PROXY
=======================================================================

CMake Warning at cmake/OpenCVDownload.cmake:202 (message):
  IPPICV: Download failed: 7;"Couldn't connect to server"

  For details please refer to the download log file:

  /home/ye/opencv-4.2.0/build/CMakeDownloadLog.txt

Call Stack (most recent call first):
  3rdparty/ippicv/ippicv.cmake:42 (ocv_download)
  cmake/OpenCVFindIPP.cmake:240 (download_ippicv)
  cmake/OpenCVFindLibsPerf.cmake:12 (include)
  CMakeLists.txt:674 (include)


-- Could not find OpenBLAS include. Turning OpenBLAS_FOUND off
-- Could not find OpenBLAS lib. Turning OpenBLAS_FOUND off
-- Could NOT find Atlas (missing: Atlas_CLAPACK_INCLUDE_DIR) 
-- A library with LAPACK API found.
-- Could NOT find JNI (missing: JAVA_INCLUDE_PATH JAVA_INCLUDE_PATH2 JAVA_AWT_INCLUDE_PATH) 
-- The imported target "vtkParseOGLExt" references the file
   "/usr/bin/vtkParseOGLExt-7.1"
but this file does not exist.  Possible reasons include:

* The file was deleted, renamed, or moved to another location.
* An install or uninstall procedure did not complete successfully.
* The installation package was faulty and contained
   "/usr/lib/cmake/vtk-7.1/VTKTargets.cmake"
but not all the files it references.

-- The imported target "vtkRenderingPythonTkWidgets" references the file
   "/usr/lib/x86_64-linux-gnu/libvtkRenderingPythonTkWidgets.so"
but this file does not exist.  Possible reasons include:
* The file was deleted, renamed, or moved to another location.
* An install or uninstall procedure did not complete successfully.
* The installation package was faulty and contained
   "/usr/lib/cmake/vtk-7.1/VTKTargets.cmake"
but not all the files it references.

-- The imported target "vtk" references the file
   "/usr/bin/vtk"
but this file does not exist.  Possible reasons include:
* The file was deleted, renamed, or moved to another location.
* An install or uninstall procedure did not complete successfully.
* The installation package was faulty and contained
   "/usr/lib/cmake/vtk-7.1/VTKTargets.cmake"
but not all the files it references.

-- The imported target