Skip directories on different filesystems when listing directory size (#221)

* Skip directories on different filesystems when listing directory size

* Only fail when one error message is given

If many error messages are printed to stderr, that means that du is
traversing a large directory tree and some errors are expected.

* Simpler heuristic for determining when to fail

Author: samdoran

src/linux_mcp_server/commands.py

@@ -184,7 +184,7 @@ class CommandGroup(BaseModel):
         ),
         "list_directories_size": CommandGroup(
             commands={
-                "default": CommandSpec(args=("du", "-b", "--max-depth=1", "{path}")),
+                "default": CommandSpec(args=("du", "-b", "--one-file-system", "{path}")),
             }
         ),
         "list_directories_name": CommandGroup(

src/linux_mcp_server/tools/storage.py

@@ -121,7 +121,9 @@ async def list_directories(
 
     returncode, stdout, stderr = await cmd.run(host=host, path=path)
 
-    if returncode != 0:
+    # The du command will exit with code 1 even if it gets some valid results.
+    # Only error in the case where we got non-zero exit code and no data in stdout.
+    if returncode != 0 and not stdout:
         raise ToolError(f"Error running command: command failed with return code {returncode}: {stderr}")
 
     # Parse the output

tests/tools/test_storage.py

@@ -282,11 +282,9 @@ async def test_list_directories_nonexistent_path(self, tmp_path, mcp_client):
         """Test list_directories with nonexistent path raises ToolError."""
         nonexistent = tmp_path / "nonexistent"
 
-        with pytest.raises(ToolError) as exc_info:
+        with pytest.raises(ToolError, match="Error running command: command failed with return code 1"):
             await mcp_client.call_tool("list_directories", arguments={"path": str(nonexistent)})
 
-        assert "Error running command: command failed with return code 1" in str(exc_info.value)
-
     async def test_list_directories_restricted_path(self, restricted_path, mcp_client):
         """Test list_directories with restricted path raises ToolError."""
         with pytest.raises(ToolError) as exc_info: