Add requirements for RHEL/CentOS

content/rke/v0.1.x/en/installation/os/_index.md

@@ -10,8 +10,40 @@ RKE runs on almost any Linux OS with Docker installed. Most of the development a
    ```
    usermod -aG docker <user_name>
    ```
+
+   See [Manage Docker as a non-root user](https://docs.docker.com/install/linux/linux-postinstall/#manage-docker-as-a-non-root-user) to see how you can configure access to Docker without using the `root` user.
 - Swap should be disabled on any worker nodes
 
+### RedHat Enterprise Linux (RHEL) / CentOS
+
+If using RedHat Enterprise Linux or CentOS, you cannot use the `root` user as [SSH user]({{< baseurl >}}/rke/v0.1.x/en/config-options/nodes/#ssh-user) due to [Bugzilla 1527565](https://bugzilla.redhat.com/show_bug.cgi?id=1527565). If you are using the Docker package supplied by RedHat / CentOS, the `dockerroot` group is automatically added to the system. You will need to edit (or create) `/etc/docker/daemon.json` to include the following:
+
+```
+{
+    "group": "dockerroot"
+}
+```
+
+Restart Docker after editing or creating the file. After restarting Docker, you can check the group permission of the Docker socket (`/var/run/docker.sock`), which should show `dockerroot` as group:
+
+```
+srw-rw----. 1 root dockerroot 0 Jul  4 09:57 /var/run/docker.sock
+```
+
+Add the SSH user you want to use to this group, this can't be the `root` user.
+
+```
+usermod -aG dockerroot <user_name>
+```
+
+To verify that the user is correctly configured, log out of the node and login with your SSH user, and execute `docker ps`:
+
+```
+ssh <user_name>@node
+$ docker ps
+CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
+```
+
 ### Software
 
 - Docker - Each Kubernetes version supports different Docker versions.