diff --git a/docker/README.md b/docker/README.md
index 1e0010e..d6abc04 100644
--- a/docker/README.md
+++ b/docker/README.md
@@ -37,6 +37,13 @@
   
   // skip docker entrypoint
   $ docker run -it --entrypoint=/bin/bash $IMAGE -i
+  
+  // delete all dangling images at once
+  // -q return only the image unique id
+  $ docker rmi $(docker images -q --filter "dangling=true")
+  
+  // remove build cache
+  $ docker builder prune
   ```
 
   
@@ -91,6 +98,21 @@
 
   
 
+* user permission
+
+```shell
+// create docker group
+$ sudo groupadd docker
+
+// add current user to group
+$ sudo usermod -aG docker ${USER}
+
+// reboot system for group privillege to take effect
+
+// test run
+$ docker run hello-world
+
+```
 * docker image versioning
 
   * Semantic Versioning ([Semver](https://medium.com/@mccode/using-semantic-versioning-for-docker-image-tags-dfde8be06699))