Hadoop Administration: Admin Command to merge fsimage and edits log
Yes, the command usage to save the Namespace is
hdfs dfsadmin -saveNamespaceThis command would save the namespace image (from memory) directly to disk which is faster than rolling and merging of edits with the fsimage stored in disk.
Before saving Namespace, make sure the safemode is turned ON.
hdfs dfsadmin -safemode enterNamenode restart is not required to save namespace.