address the comments

Signed-off-by: jason yang <[email protected]>

index.rst

@@ -88,7 +88,6 @@ networking and security configuration.
    Network Options <networking>
    Limiting Container Resources <cgroups>
    Application Checkpointing <checkpoint>
-   Monitoring <monitoring>
 
 *************
 Compatibility

mpi.rst

@@ -262,14 +262,21 @@ If the host MPI is Open MPI, the definition file looks like:
 Using --sharens mode
 ====================
 
-By default, with unprivileged setup, each process spawned by MPI runs in its own user namespace. This will 
-bring problems as observed :ref:`in this issue <mpi-issue>`. The new ``--sharens`` flag will
-help move all spawned processes into the same user namespace, similar to what is done with {Project} SUID mode. 
+Default in unprivileged user namespace mode. Each process spawned by MPI runs in its own user namespace. This will 
+bring problems as observed :ref:`in this issue <mpi-issue>`. The new ``--sharens`` flag will 
+move all spawned processes into the same user namespace, similar to what is done with {Project} SUID mode. 
 
 .. code::
 
    mpirun -np 2 apptainer exec --sharens $MY_CONTAINER ./a.out
 
+.. note::
+
+   Note that ``--sharens`` flag requires all spawned processes having the same parent process. This is because these
+   child processes will join the same namespace identified using the parent process id. To meet the requirement, {Project} 
+   containers should be launched by the same process, e.g. mpirun, and all these containers should be running on the same host. 
+   ``--sharens`` does not support sharing the same namespace accross different hosts.
+
 Running an MPI Application
 ==========================