diff --git a/.github/workflows/docker.yaml b/.github/workflows/docker.yaml
index bd4d002..e82d673 100644
--- a/.github/workflows/docker.yaml
+++ b/.github/workflows/docker.yaml
@@ -85,7 +85,7 @@ jobs:
           docker push ultralytics/ultralytics:${{ matrix.tags }}
 
       - name: Notify on failure
-        if: github.event_name == 'push' && (cancelled() || failure())
+        if: github.event_name == 'push' && failure()  # do not notify on cancelled() as cancelling is performed by hand
         uses: slackapi/slack-github-action@v1.24.0
         with:
           payload: |
diff --git a/tests/test_python.py b/tests/test_python.py
index 766c9df..bda1d38 100644
--- a/tests/test_python.py
+++ b/tests/test_python.py
@@ -295,10 +295,8 @@ def test_events():
 
 
 def test_utils_init():
-    from ultralytics.utils import (get_git_branch, get_git_origin_url, get_ubuntu_version, is_github_actions_ci,
-                                   is_ubuntu)
+    from ultralytics.utils import get_git_branch, get_git_origin_url, get_ubuntu_version, is_github_actions_ci
 
-    is_ubuntu()
     get_ubuntu_version()
     is_github_actions_ci()
     get_git_origin_url()
diff --git a/ultralytics/engine/exporter.py b/ultralytics/engine/exporter.py
index 6800ea5..3398c05 100644
--- a/ultralytics/engine/exporter.py
+++ b/ultralytics/engine/exporter.py
@@ -424,7 +424,9 @@ class Exporter:
                 'https://github.com/pnnx/pnnx/.\nNote PNNX Binary file must be placed in current working directory '
                 f'or in {ROOT}. See PNNX repo for full installation instructions.')
             _, assets = get_github_assets(repo='pnnx/pnnx', retry=True)
-            asset = [x for x in assets if ('macos' if MACOS else 'ubuntu' if LINUX else 'windows') in x][0]
+            system = 'macos' if MACOS else 'ubuntu' if LINUX else 'windows'  # operating system
+            asset = [x for x in assets if system in x][0] if assets else \
+                f'https://github.com/pnnx/pnnx/releases/download/20230816/pnnx-20230816-{system}.zip'  # fallback
             attempt_download_asset(asset, repo='pnnx/pnnx', release='latest')
             unzip_dir = Path(asset).with_suffix('')
             pnnx = ROOT / pnnx_filename  # new location
diff --git a/ultralytics/utils/__init__.py b/ultralytics/utils/__init__.py
index e8a912e..8d07306 100644
--- a/ultralytics/utils/__init__.py
+++ b/ultralytics/utils/__init__.py
@@ -571,9 +571,10 @@ def get_ubuntu_version():
     Returns:
         (str): Ubuntu version or None if not an Ubuntu OS.
     """
-    with contextlib.suppress(FileNotFoundError, AttributeError):
-        with open('/etc/os-release') as f:
-            return re.search(r'VERSION_ID="(\d+\.\d+)"', f.read())[1]
+    if is_ubuntu():
+        with contextlib.suppress(FileNotFoundError, AttributeError):
+            with open('/etc/os-release') as f:
+                return re.search(r'VERSION_ID="(\d+\.\d+)"', f.read())[1]
 
 
 def get_user_config_dir(sub_dir='Ultralytics'):