KnowledgeBase/CII.md

@@ -1387,8 +1387,28 @@ More details on Fast DDS Qos: https://fast-dds.docs.eprosima.com/en/latest/fastd
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+### DDS SHM Shared Memory Startup Errors \[MAL DDS\]
 
+**Problem**
+
+On startup of DDS application an error about Shared Memory (SHM) is displayed, for example:
+RTPS SHM: "port marked as not ok"
+
+**Solution**
 
+The SHM transport is one of the default transports of a DDS application and is used to communicate to peers on the same host. The relevant files created by DDS are visible in /dev/shm/*fast*.
+If a DDS does not exit cleanly, it may leave the SHM files present, possibly leading to errors when the application restarts, and in any case polluting the /dev/shm/ folder.
+
+To clean up the SHM files used by DDS the following command is provided:
+```plaintext
+    fastdds shm clean
+```
+
+---
+
+---
+
+---
 ### Discovery over multiple NICs \[MAL DDS\]
 
 **Problem**