diff --git a/.github/actions/ct-test/action.yml b/.github/actions/ct-test/action.yml
index d4eaa60f0..e0d984c59 100644
--- a/.github/actions/ct-test/action.yml
+++ b/.github/actions/ct-test/action.yml
@@ -14,6 +14,28 @@ inputs:
 runs:
   using: composite
   steps:
+      - name: System info
+        shell: ${{ env.SHELL }}
+        run: |
+          ARCH=$(uname -m)
+          echo <<-EOF
+            ## Setup
+            Architecture: $ARCH
+            - $(uname -a)
+            - $(nix --version || echo 'nix not present')
+            - $(bash --version | grep -m1 "")
+            - $(python3 --version)
+            - $(${{ inputs.cross_prefix }}${CC} --version | grep -m1 "")
+          EOF
+          cat >> $GITHUB_STEP_SUMMARY <<-EOF
+            ## Setup
+            Architecture: $ARCH
+            - $(uname -a)
+            - $(nix --version || echo 'nix not present')
+            - $(bash --version | grep -m1 "")
+            - $(python3 --version)
+            - $(${{ inputs.cross_prefix }}${CC} --version | grep -m1 "")
+          EOF
       - shell: ${{ env.SHELL }}
         run: |
           make clean
diff --git a/.github/actions/setup-shell/action.yml b/.github/actions/setup-shell/action.yml
index bb36a3802..ddfeba58e 100644
--- a/.github/actions/setup-shell/action.yml
+++ b/.github/actions/setup-shell/action.yml
@@ -10,6 +10,9 @@ inputs:
   nix-cache:
     description: Determine whether to enable nix cache
     default: 'false'
+  nix-cache-prefix:
+    description: Fixed prefix of ID of Github cache entries that should be removed.
+    required: false
   nix-verbose:
     description: Determine wether to suppress nix log or not
     default: 'false'
@@ -35,6 +38,7 @@ runs:
         verbose: ${{ inputs.nix-verbose }}
         cache: ${{ inputs.nix-cache }}
         script: ${{ inputs.script }}
+        cache_prefix: ${{ inputs.nix-cache-prefix }}
     - name: Set custom shell
       shell: bash
       if: ${{ inputs.nix-shell == '' }}
diff --git a/.github/workflows/ct-tests.yml b/.github/workflows/ct-tests.yml
index 89c82469e..296e09acf 100644
--- a/.github/workflows/ct-tests.yml
+++ b/.github/workflows/ct-tests.yml
@@ -44,6 +44,7 @@ jobs:
           gh_token: ${{ secrets.GITHUB_TOKEN }}
           nix-shell: ${{ matrix.nix-shell }}
           nix-cache: true
+          nix-cache-prefix: valgrind-${{ runner.os }}-${{ runner.arch }}
       - name:  Build and run test (-Oz)
         # -Oz got introduced in gcc12
         if: ${{ matrix.nix-shell !=  'ci_valgrind-varlat_gcc48' && matrix.nix-shell !=  'ci_valgrind-varlat_gcc49' && matrix.nix-shell !=  'ci_valgrind-varlat_gcc7' && matrix.nix-shell !=  'ci_valgrind-varlat_gcc11'}}