Master node issue

Issue

I have a cluster, which has for example 3 nodes, where the mpd.hosts file contains:

$ cat mpd.hosts
node2
node3

The master node, which is node1 is not listed in the mpd.hosts file. The shell commands:

$ mpdboot -r ssh -n 2 -f ~/mpd.hosts
$ mpiexec -n 4 /bin/hostname
which are issued from node1 reveal the following:
node1
node1
node2
node2

 

Solution

By design, the master node (i.e., the node where the mpiexec command is launched from) needs to have a daemon running. If you want to run your application on node2 and node3, you can use the -host options with the mpiexec command as follows:

$ mpdboot -r ssh -n 3 -f ~/mpd.hosts
$ mpiexec -n 2 -host node2 /bin/hostname : -n 2 -host node3 /bin/hostname
Or simply to use the -nolocal option for mpiexec as follows:
$ mpdboot -r ssh -n 3 -f ~/mpd.hosts
$ mpiexec -nolocal -n 4 /bin/hostname

This will run the hostname command on nodes node2 and node3 only, even though there are three mpd daemons total.

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