<no title> — PMIx Reference Run Time Environment 3.0.2a1 documentation

PRRTE supports several levels of user-specified host lists based on an established precedence order. Users can specify a default hostfile that contains a list of nodes to be used by the DVM. Only one default hostfile can be provided for a given DVM. In addition, users can specify a hostfile that contains a list of nodes to be used for a DVM, or can provide a comma-delimited list of nodes to be used for that DVM via the `--host` command line option.

The precedence order applied to these various options depends to some extent on the local environment. The following table illustrates how host and hostfile directives work together to define the set of hosts upon which a DVM will execute in the absence of a resource manager (RM):

Default hostfile | host | hostfile | Result
--- | --- | --- | ---
unset | unset | unset | The DVN will consist solely of the local host where the DVM was started.
unset | set | unset | Host option defines resource list for the DVM.
unset | unset | set | Hostfile option defines resource list for the DVM.
unset | set | set | Hostfile option defines resource list for the DVM, then host filters the list to define the final set of nodes to be used by the DVM
set | unset | unset | Default hostfile defines resource list for the DVM
set | set | unset | Default hostfile defines resource list for the DVM, then host filters the list to define the final set of nodes to be used by the DVM
set | set | set | Default hostfile defines resource list for the DVM, then hostfile filters the list, and then host filters the list to define the final set of nodes to be used by the DVM

This changes somewhat in the presence of an RM as that entity specifies the initial allocation of nodes. In this case, the default hostfile, hostfile and host directives are all used to filter the RM’s specification so that a user can utilize different portions of the allocation for different DVMs. This is done according to the same precedence order as in the prior table, with the RM providing the initial pool of nodes.