Hello, we have been hit observing a strange behavior with OpenMPI 1.6.3
strace -f /share/apps/openmpi/1.6.3/bin/mpiexec -n 2 --nooversubscribe --display-allocation --display-map --tag-output /share/apps/gamess/2011R1/gamess.2011R1.x /state/partition1/rmurri/29515/exam01.F05 -scr /state/partition1/rmurri/29515 ====================== ALLOCATED NODES ====================== Data for node: nh64-1-17.local Num slots: 0 Max slots: 0 Data for node: nh64-1-17 Num slots: 2 Max slots: 0 ================================================================= ======================== JOB MAP ======================== Data for node: nh64-1-17 Num procs: 2 Process OMPI jobid: [37108,1] Process rank: 0 Process OMPI jobid: [37108,1] Process rank: 1 ============================================================= As you can see, the host file lists the *unqualified* local host name; OpenMPI fails to recognize that as the same host where it is running, and uses `ssh` to spawn a remote `orted`, as use of `strace -f` shows: Process 16552 attached [pid 16552] execve("//usr/bin/ssh", ["/usr/bin/ssh", "-x", "nh64-1-17", "OPAL_PREFIX=/share/apps/openmpi/1.6.3 ; export OPAL_PREFIX; PATH=/share/apps/openmpi/1.6.3/bin:$PATH ; export PATH ; LD_LIBRARY_PATH=/share/apps/openmpi/1.6.3/lib:$LD_LIBRARY_PATH ; export LD_LIBRARY_PATH ; DYLD_LIBRARY_PATH=/share/apps/openmpi/1.6.3/lib:$", "--daemonize", "-mca", "ess", "env", "-mca", "orte_ess_jobid", "2431909888", "-mca", "orte_ess_vpid", "1", "-mca", "orte_ess_num_procs", "2", "--hnp-uri", "\"2431909888.0;tcp://10.1.255.237:33154\"", "-mca", "plm", "rsh"], ["OLI235=/state/partition1/rmurri/29515/exam01.F235", ... If the machine file lists the FQDNs instead, `mpiexec` spawns the jobs directly via fork()/exec(). This seems related to the fact that each compute node advertises 127.0.1.1 as the IP address associated to its hostname: $ ssh nh64-1-17 getent hosts nh64-1-17 127.0.1.1 nh64-1-17.local nh64-1-17 Indeed, if I change /etc/hosts so that a compute node associates a "real" IP with its hostname, `mpiexec` works as expected. Is this a known feature/bug/easter egg? For the record: using OpenMPI 1.6.3 on Rocks 5.2. Thanks, on behalf of the GC3 Team Sergio :) GC3: Grid Computing Competence Center http://www.gc3.uzh.ch/ University of Zurich Winterthurerstrasse 190 CH-8057 Zurich Switzerland Tel: +41 44 635 4222 Fax: +41 44 635 6888