Figure 4-9 Users’ job launch overview and events sequence There are three components that are involved in the job launch:  The dashed lines in Figure 4-9 indicate optional operations.  After IBM Spectrum LSF decides to start a job by using the CSM infrastructure, it calls  csm_allocation_create  to reserve nodes for a job, run the job prolog, create the Job Step  Manager (JSM) (PMIx) server, and launch a user script or executable file on the LN. As part  of the CSM allocation, the CSM database is updated to include the job start information.  Then, the compute nodes are put into job run mode and are accessible to the job owner. The  jsm  daemon creates a job step launch tree on all the nodes that are determined by a  csm_allocation_query  call. This job step tree is created on behalf of the job that is allocated  with  csm_allocation create . Then, user job steps can be launched by the user with the  jsrun command. This command communicates with the  jsm  daemon on the LN through a UNIX  socket by passing job step requests. As part of the job step start and end, IBM JSM calls  CSM to record step-specific information in the CSM database. After the last job step  completes, the user script or executable file that is launched by IBM Spectrum LSF exits and  IBM Spectrum LSF stops the  jsm  daemon. IBM Spectrum LSF then releases resources after  calling the job epilog with a call to  csm_allocation_delete . Then, the job resource usage is  stored in the CSM database; the job is complete; and the node resources can be reused. Chapter 4. Reference architecture  47 1. The workload manager (WLM) (IBM Spectrum LSF) 2. The CSM 3. The Message Passing Interface (MPI) Runtime Environment (RTE)