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NOTE: The interfaces of flux-core are being actively developed and are not yet stable. The github issue tracker is the primary way to communicate with the developers.

See also our Online Documentation.


flux-core implements the communication layer and lowest level services and interfaces for the Flux resource manager framework. It consists of a distributed message broker, broker plug-in modules that implement various distributed services, and an API and set of utilities to utilize these services.

flux-core is intended to be the first building block used in the construction of a site-composed Flux resource manager. Other building blocks are also in development under the flux-framework github organization, including a fully functional workload scheduler.

Framework projects use the C4 development model pioneered in the ZeroMQ project and forked as Flux RFC 1. Flux licensing and collaboration plans are described in Flux RFC 2. Protocols and API's used in Flux will be documented as Flux RFC's.

Build Requirements

Click to expand and see our full dependency table

flux-core requires the following packages to build:

redhat ubuntu version note
autoconf autoconf
automake automake
libtool libtool
make make
pkgconfig pkg-config
libsodium-devel libsodium-dev >= 1.0.14
zeromq4-devel libzmq3-dev >= 4.0.4
czmq-devel libczmq-dev >= 3.0.1
jansson-devel libjansson-dev >= 2.6
libuuid-devel uuid-dev
lz4-devel liblz4-dev
hwloc-devel libhwloc-dev >= v1.11.1
sqlite-devel libsqlite3-dev >= 3.0.0
lua lua5.1 >= 5.1, < 5.5
lua-devel liblua5.1-dev >= 5.1, < 5.5
lua-posix lua-posix 1
python36-devel python3-dev >= 3.6
python36-cffi python3-cffi >= 1.1
python36-yaml python3-yaml >= 3.10.0
python36-jsonschema python3-jsonschema >= 2.3.0
phthon3-sphinx python3-sphinx 2

*Note 1 - Due to a long standing packaging bug in lua-posix-33.4.0-2 on Ubuntu bionic, you may wish to install lua-posix via luarocks on that distro.

*Note 2 - only needed if optional man pages are to be created.

The following optional dependencies enable additional testing:

redhat ubuntu version
aspell aspell
aspell-en aspell-en
valgrind-devel valgrind
mpich-devel libmpich-dev
jq jq
Installing RedHat/CentOS Packages
yum install autoconf automake libtool make pkgconfig libsodium-devel zeromq4-devel czmq-devel libuuid-devel jansson-devel lz4-devel hwloc-devel sqlite-devel lua lua-devel lua-posix python36-devel python36-cffi python36-yaml python36-jsonschema python3-sphinx aspell aspell-en valgrind-devel mpich-devel jq
Installing Ubuntu Packages
apt install autoconf automake libtool make pkg-config libsodium-dev libzmq3-dev libczmq-dev uuid-dev libjansson-dev liblz4-dev libhwloc-dev libsqlite3-dev lua5.1 liblua5.1-dev lua-posix python3-dev python3-cffi python3-yaml python3-jsonschema python3-sphinx aspell aspell-en valgrind libmpich-dev jq
Building from Source
./   # skip if building from a release tarball
make check

Bootstrapping a Flux instance

A Flux instance is composed of a set of flux-broker processes that bootstrap via PMI (e.g. under another resource manager), or locally via the flux start command.

No administrator privilege is required to start a Flux instance as described below.

Single node session

To start a Flux instance (size = 8) on the local node for testing:

src/cmd/flux start --size 8

A shell is spawned that has its environment set up so that Flux commands can find the message broker socket. When the shell exits, the session exits.

SLURM session

To start a Flux instance (size = 64) on a cluster using SLURM, first ensure that MUNGE is set up on your cluster, then:

srun --pty --mpi=none -N64 src/cmd/flux start

The srun --pty option is used to connect to the rank 0 shell. When you exit this shell, the session terminates.

Flux commands

Within a session, the path to the flux command associated with the session broker will be prepended to PATH, so use of a relative or absolute path is no longer necessary.

To see a list of commonly used commands run flux with no arguments, flux help, or flux --help

$ flux help
  -h, --help             Display this message.
  -v, --verbose          Be verbose about environment and command search

Common commands from flux-core:
   broker             Invoke Flux message broker daemon
   content            Access instance content storage
   cron               Schedule tasks on timers and events
   dmesg              manipulate broker log ring buffer
   env                Print or run inside a Flux environment
   event              Send and receive Flux events
   exec               Execute processes across flux ranks
   get,set,lsattr     Access, modify, and list broker attributes
   hwloc              Control/query resource-hwloc service
   keygen             generate keys for Flux security
   kvs                Flux key-value store utility
   logger             create a Flux log entry
   module             manage Flux extension modules
   ping               measure round-trip latency to Flux services
   proxy              Create proxy environment for Flux instance
   ps                 List subprocesses managed by brokers
   start              bootstrap a local Flux instance
   submit             submit job requests to a scheduler
   user               Flux user database client

Most of these have UNIX manual pages as flux-<sub-command>(1), which can also be accessed using ./flux help <sub-command>.

A note about PMI

When flux is launched, it requires PMI-1 in order to bootstrap. It can use PMI-1 in one of two ways, by inheriting a file descriptor via the PMI_FD environment variable, or by dlopening a PMI library. The library name is, unless overridden by the PMI_LIBRARY environment variable. If a PMI library is not found, flux falls back to "singleton" operation, where each broker is an independent flux instance. The PMI bootstrap may be traced by setting the FLUX_PMI_DEBUG environment variable.

When flux launches flux or an MPI job, it provides PMI-1 to bootstrap the MPI's runtime. It offers a PMI server and sets the PMI_FD environment variable to point to an open file descriptor connected to it. It also offers a library that can be dlopened.

If your system process manager uses PMIx, the compatibility library provided by the PMIx project should be sufficient to bootstrap flux. If your version of PMIx was not built with the compatibility libraries installed, you may build libpmix as a separate package to get them installed.


SPDX-License-Identifier: LGPL-3.0