Merge pull request #230 from nickaj/23072025_warning_cephfs_permissions

23072025 warning cephfs permissions

Author: nickaj

docs/services/virtualmachines/sharedfs.md

@@ -2,9 +2,14 @@
 
 ## Introduction
 
-EIDF allows projects with storage space allocated on our CephFS filesystem to mount that space on different compute resources such as EIDF Virtual Machines Service (VMS).
+EIDF allows projects with storage space allocated on our CephFS filesystem to access that space on different compute resources such as the EIDF Virtual Machines Service (VMS).
 
-Mounting is done at a project level, so the whole project CephFS tree is mounted. For users who have used our Cerebras or Cirrus services, the whole of the top-level project directory is mounted, e.g. `/home/eidf124` on Cirrus is the same as `/home/eidf124` on the VM, and users can manipulate files in that directory.
+On VMs, mounting is done at a project level, i.e. the project subtree part of CephFS is mounted. For users who have used our Cerebras or Cirrus services, `/home/eidf124` on Cirrus is the same as `/home/eidf124` on the VM, and users can manipulate files in that directory. However, such VMs would not typically have access to `/home/eidf421` or other project directories.
+
+!!! note
+    Changing file properties on CephFS on a VM will cause the effect to be visible wherever the file is visible, ie on other systems.
+
+If you set a file stored on CephFS to be world readable on your VM, it will also be world readable (i.e. viewable by any user) on shared-access systems such as Cerebras or Cirrus. This also applies to files in the top-level shared directory. For example, files in `/home/eidf124/shared` are visible wherever `/home/eidf124` is mounted.
 
 ## Pre-requisites