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Homogeneous user ID space
ParaStation5 Administrator's Guide 23
etc/passwd. Usage of common authentication schemes like NIS is not required and therefore limits user
management to the frontend nodes.
Authentication of users is restricted to login or frontend nodes and is outside of the scope of ParaStation.
5.10. Homogeneous user ID space
As explained in the previous section, ParaStation uses only user and group IDs for starting up remote
processes. Therefore, all processes will have identical user and group IDs on all nodes.
A homogeneous user ID space is stretched across the entire cluster.
5.11. Single system view
The ParaStation administration tool collects and displays information from all or a selected subset of nodes
in the cluster. Actions can be initiated on each node and will be automatically and transparently forwarded
to the destination node(s), if necessary. From a management perspective, all the nodes are seen as a
homogeneous system. Thus, the administrator will have a single system view of the cluster.
5.12. Parallel shell tool
ParaStation provides a parallel shell tool called psh, which allows to run commands on all or selected nodes
of the cluster in parallel. The output of the individual commands is presented in a sophisticated manner,
showing common parts and differences.
psh may also be used to copy files to all nodes of the cluster in parallel.
This command is not intended to run interactive commands in parallel, but to run a single task in parallel
on all or a bunch of nodes and prepare the output to be easily read by the user.
5.13. Nodes and CPUs
Though ParaStation by default tries to use a dedicated CPU per compute process, there is currently no
way to bind a process to a particular CPU. Therefore, there is no guarantee, that each process will use its
own CPU. But due to the nature of parallel tasks, the operating system scheduler will typically distribute
each process to its own CPU.
Care must be taken if the hardware is able to simulate virtual CPUs, e.g. Intel Xeon CPUs using
Hyperthreading. The ParaStation daemon detects virtual CPUs and uses all the virtual CPUs found for
placing processes. Detecting virtual CPUs requires that the kernel module cpuid is loaded prior to starting
the ParaStation daemon. Use
# psiadmin -c "s hw"
Node CPUs Available Hardware
0 4/ 2 ethernet p4sock
1 4/ 2 ethernet p4sock
to show the number of virtual and physical CPUs per node.
It's possible to spawn more processes than physical or virtual CPUs are available on a node ("overbooking").
See ParaStation5 User's Guide for details.