Improve error handling when stop a scan.

CHANGELOG.md

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ### Changed
 - Set loglevel to debug for some message. [#159](https://github.com/greenbone/ospd/pull/159)
+- Improve error handling when stop a scan. [#163](https://github.com/greenbone/ospd/pull/163)
 
 ### Fixed
 - Fix set permission in unix socket. [#157](https://github.com/greenbone/ospd/pull/157)

ospd/ospd.py

@@ -659,7 +659,12 @@ def stop_scan(self, scan_id):
         except AttributeError:
             logger.debug('%s: The scanner task stopped unexpectedly.', scan_id)
 
-        os.killpg(os.getpgid(scan_process.ident), 15)
+        try:
+            os.killpg(os.getpgid(scan_process.ident), 15)
+        except ProcessLookupError as e:
+            logger.info('%s: Scan already stopped %s.',
+                        scan_id, scan_process.ident)
+
         if scan_process.ident != os.getpid():
             scan_process.join()
         logger.info('%s: Scan stopped.', scan_id)