6.2. Hostfiles — PMIx Reference Run Time Environment 3.0.2a1 documentation

# 6.2. Hostfiles

Hostfiles (sometimes called “machine files”) are a combination of two things:

1. A listing of hosts on which to launch processes.

2. Optionally, limit the number of processes which can be launched on each host.

## 6.2.1. Syntax

Hostfile syntax consists of one node name on each line, optionally including a designated number of “slots”:

    # This is a comment line, and will be ignored
    node01  slots=10
    node13  slots=5

    node15
    node16
    node17  slots=3
    ...

Blank lines and lines beginning with a `#` are ignored.

A “slot” is the PRRTE term for an allocatable unit where we can launch a process. See this section for a longer description of slots.

In the absence of the `slot` parameter, PRRTE will assign either the number of slots to be the number of CPUs detected on the node or the resource manager-assigned value if operating in the presence of an RM.

Important

If using a resource manager, the user-specified number of slots is capped by the RM-assigned value.