Hostfiles (sometimes called “machine files”) are a combination of two things:
A listing of hosts on which to launch processes.
Optionally, limit the number of processes which can be launched on each host.
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 the section on definition of the term
slot 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
If using a resource manager, the user-specified number of slots is capped by the RM-assigned value.