Use shallow clones for the submodules

CMakeLists.txt

@@ -30,7 +30,7 @@ if(GIT_FOUND AND EXISTS "${PROJECT_SOURCE_DIR}/.git")
     option(GIT_SUBMODULE "Check submodules during build" ON)
     if(GIT_SUBMODULE)
         message(STATUS "Submodule update")
-        execute_process(COMMAND ${GIT_EXECUTABLE} submodule update --init --recursive --checkout
+        execute_process(COMMAND ${GIT_EXECUTABLE} submodule update --init --recursive --checkout --depth 1
                         WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
                         RESULT_VARIABLE GIT_SUBMOD_RESULT)
         if(NOT GIT_SUBMOD_RESULT EQUAL "0")

scripts/docker/Centos8

@@ -38,9 +38,8 @@ RUN \
 
 RUN \
   cd /external && \
-  git clone https://github.com/casacore/casacore.git && \
+  git clone https://github.com/casacore/casacore.git --branch v3.3.0 --depth 1 && \
   cd /external/casacore && \
-  git checkout v3.3.0 && \
   mkdir build && \
   cd build && \
   cmake .. -DBUILD_PYTHON=OFF -DBUILD_TESTING=OFF && \

scripts/docker/run.sh

-sudo docker build -f Ubuntu18 ../..
+sudo docker build -f Ubuntu20 ../..