update recommended workaround

Signed-off-by: Yoshiaki Senda <[email protected]>

mpi.rst

@@ -252,21 +252,9 @@ If the host MPI is Open MPI, the definition file looks like:
 
    .. code::
 
-      # Workaround 1
-      # (a) Use --ipc apptainer exec option
-      # See https://apptainer.org/docs/user/latest/docker_and_oci.html#namespace-device-isolation
-      mpirun -np 2 apptainer exec --ipc $MY_CONTAINER ./a.out
-
-      # (b) Use APPTAINER_UNSHARE_IPC=1 or APPTAINER_UNSHARE_IPC=true
-      # See https://apptainer.org/docs/user/latest/appendix.html#u
-      APPTAINER_UNSHARE_IPC=1 mpirun -np 2 apptainer exec $MY_CONTAINER ./a.out
-
-   .. code::
-
-      # Workaround 2
-      # Use UCX environment variable UCX_POSIX_USE_PROC_LINK set to n
-      # See https://github.com/apptainer/apptainer/issues/769
-      UCX_POSIX_USE_PROC_LINK=n mpirun -np 2 apptainer exec $MY_CONTAINER ./a.out
+      # Workaround
+      # Use System V shared memory trasnport
+      mpirun -np 2 -mca pml ucx -x UCX_TLS=sysv,ib apptainer exec $MY_CONTAINER ./a.out
 
 Running an MPI Application
 ==========================