Update maintenance.md

maintenance.md

@@ -76,3 +76,8 @@ First umount the fs from all the client, then stop all the metadata servers. Aft
 ```
 ceph fs rm cephfs --yes-i-really-mean-it
 ```
+### Crash Warning
+After checking with `ceph crash ls-new`, they can be cleaned with
+```
+for id in `ceph crash ls-new | awk '{print $1}' | awk '{if(NR>1)print}'`;do ceph crash archive $id;done
+```