Here we define Flux-specific and general HPC and workload management terms used in our documentation that may not be familiar to all readers.

enclosing instance

The Flux instance that a process naturally interacts with. It is the instance referred to by the FLUX_URI environment variable, or if that is not set, it is the system instance.


A job is said to be expedited if its urgency is set to the maximum value of 31. An expedited job's priority is always set to the maximum value.


A common string representation of time duration, defined by 23/Flux Standard Duration. Example: 2.5h.


A Flux user that is not the instance owner. Guests are only allowed to run in a Flux instance configured for multi-user support, normally a system instance.


A job is said to be held if its urgency is set to zero. This prevents it from being considered for scheduling until the urgency is raised.


A compact string representation of a list of hostnames, defined by 29/Hostlist Format. Example: fluke[0-127,130].


A compact string representation of a set of non-negative integers, defined by 22/Idset String Representation. Example: 2,4,6,1-100.


The Independent Minister of Privilege. The simple setuid root component of Flux, from the flux-security project, that allows an instance owner to perform a limited set of tasks on behalf of a guest user in a multi-user Flux instance.

initial program

A user-defined program, such as a batch script, launched on the first node of a Flux instance. Its purpose is to launch and monitor a workload. Once it is complete, the instance exits.

instance owner

The user that started the Flux instance. The instance owner has control over all aspects of the Flux instance's operation.


The smallest unit of work that can be allocated resources and run by Flux. A job can be a Flux instance which in turn can run more jobs.


The JSON or YAML object representing a Flux job request, defined by 14/Canonical Job Specification (the general specification) and 25/Job Specification Version 1 (the current version). It includes the abstract resource requirements of the job and instructions for job execution.


The order in which the scheduler considers jobs. By default, priority is derived from the urgency and submit time, but a priority plugin can be used to override this calculation.


The JSON object used by Flux to represent a concrete resource set. See 20/Resource Set Specification Version 1.

resource inventory

The concrete set of resources managed by a given Flux instance.


The Flux component that fulfills resource allocation requests from the resource inventory. Abstract resource requirements are extracted from the user-provided jobspec, and fulfilled with a resource set expressed as R. In addition to fitting concrete resources to abstract requests, the scheduler must balance goals such as fairness and resource utilization when it decides upon a schedule for fulfilling competing requests.


The abstract resource requirements of one task.


In other workload managers, a job step is a unit of work within a job. Flux, which has a robust recursive definition of a job, does not use this term.

system instance

A multi-user Flux instance running as the primary resource manager on a cluster. The system instance typically runs as an unprivileged system user like flux, is started by systemd(1), and allows guest users to run jobs.


A compact mapping between job task ranks and node IDs, defined by 34/Flux Task Map.


Tree based overlay network. Flux brokers are interconnected with one.


A job attribute that the user sets to indicate how urgent the work is. The range is 0 to 31, with a default value of 16. Urgency is defined by 30/Job Urgency.