increase default MPI_Init wait threshold

Author: sekelle

docs/guides/gb25.md

@@ -41,7 +41,12 @@ The fix is to update how the squashfs file for the uenv or container used by you
 ```console title="set lustre striping on uenv squashfs file"
 $ uenv image inspect prgenv-gnu/24.11:v2 --format='{sqfs}'
 /capstor/scratch/cscs/bcumming/.uenv-images/images/6068794b820fb4dd91019d020d6d98334a2f9fd23035a5e4a2f72f9dda5f1260/store.squashfs
-$ lfs setstripe --stripe-count -1 --stripe-size 4M $(uenv image inspect prgenv-gnu/24.11:v2 --format='{sqfs}')
+$ lfs setstripe --stripe-count -1 --stripe-size 1M $(uenv image inspect prgenv-gnu/24.11:v2 --format='{sqfs}')
+```
+
+As an additional precaution, we recommend to increase the default wait threshold for `MPI_Init` from 180 seconds to 300.
+```console title="increase MPI initialization time-out"
+$ export PMI_MMAP_SYNC_WAIT_TIME=300
 ```
 
 !!! todo "update this with the final guidance"