Flux broker attributes are broker parameters with a scope of a single broker rank. They may be listed with flux-lsattr(1) and queried with flux-getattr(1).

Attributes should be considered read-only, unless annotated below with:


The attribute may be set on the flux-broker(1) command line with --setattr=NAME=VALUE.


The attribute may be updated on a running broker with flux-setattr(1).



The rank of the local broker.


The number of broker ranks in the flux instance


The version of flux-core that was used to build this broker.

rundir [Updates: C]

A temporary directory where the broker's UNIX domain sockets are located. In addition, if statedir is not set, this directory is used by the content backing store (if applicable). By default, each broker rank creates a unique rundir in $TMPDIR and removes it on exit. If rundir is set on the command line, beware exceeding the UNIX domain socket path limit described in unix(7), as low as 92 bytes on some systems. To support the flux-start(1) --test-size option where multiple brokers share a rundir, if rundir is set to a pre-existing directory, the directory is not removed by the broker on exit. In most cases this attribute should not be set by users.

statedir [Updates: C]

A directory in which persistent state is stored by the Flux broker. For example, content backing store data is stored here to facilitate restarts. If unset, this data goes to rundir where it is cleaned up on instance shutdown. If set, this directory must exist and be owned by the instance owner. Default: unset.


The numeric userid of the owner of this Flux instance.

local-uri [Updates: C]

The Flux URI that the local connector binds to for accepting connections from local Flux clients. The name must begin with local:// and the path must refer to a unix(7) domain socket in an existing directory.


The value of the broker's FLUX_URI environment variable. This is the URI that should be passed to flux_open(3) to establish a connection to the enclosing instance.


The nesting level of this Flux instance, or 0 if there is no enclosing Flux instance.


The Flux job ID of this Flux instance, if it was launched by Flux as a job. The value is obtained from PMI_KVS_Get_my_name() which may be something other than a Flux job ID if Flux was started by another means.


The value of the broker's FLUX_KVS_NAMESPACE environment variable. This is the KVS namespace assigned to this Flux instance by its enclosing instance, if it was launched by Flux as a job.


An RFC 29 hostlist in broker rank order. This value may be used to translate between broker ranks and hostnames.


A string representing the process mapping of broker ranks in the Flux Task Map format described in RFC 34. For example, [[0,16,1,1]] means the instance has one broker per node on 16 nodes, and [[0,1,16,1]] means it has 16 brokers on one node.

broker.critical-ranks [Updates: C]

An RFC 22 idset representing broker ranks that are considered critical to instance operation. The broker notifies the job execution system in the parent instance of these ranks such that a fatal job exception is raised when a failing node or other error occurs affecting any rank in this set. Default: rank 0 plus any other overlay network routers.

broker.boot-method [Updates: C]

A URI representing the method used to bootstrap Flux. Valid values are config (boot via TOML config file), simple (use the PMI-1 simple wire protocol), libpmi[:path] (use a PMI-1 shared library), or single (standalone size=1). Additional boot methods may be provided by plugins.


The process id of the local broker.

broker.quorum [Updates: C]

An RFC 22 idset representing broker ranks that are required to be online before the rank 0 broker enters the RUN state and starts the initial program, if any. Default: all ranks.

broker.quorum-timeout [Updates: C]

The amount of time (in RFC 23 Flux Standard Duration format) that the rank 0 broker waits for the broker.quorum set to come online before aborting the Flux instance. Default: 60s.

broker.rc1_path [Updates: C]

The path to the broker's rc1 script. Default: ${prefix}/etc/flux/rc1.

broker.rc3_path [Updates: C]

The path to the broker's rc3 script. Default: ${prefix}/etc/flux/rc1.

broker.exit-restart [Updates: C, R]

A numeric exit code that the broker uses to indicate that it should not be restarted. This is set by the systemd unit file. Default: unset.


Timestamp of broker startup from flux_reactor_now(3).


The value of the broker's FLUX_CONNECTOR_PATH environment variable.


The value of the broker's FLUX_EXEC_PATH environment variable.


The value of the broker's FLUX_MODULE_PATH environment variable.


The value of the broker's FLUX_PMI_LIBRARY_PATH environment variable.

conf.shell_initrc [Updates: C, R]

The path to the flux-shell(1) initrc script. Default: ${prefix}/etc/flux/shell/initrc.lua.

conf.shell_pluginpath [Updates: C, R]

The list of colon-separated directories to be searched by flux-shell(1) for shell plugins. Default: ${prefix}/lib/flux/shell/plugins.

config.path [Updates: see below]

A directory containing *.toml config files for this Flux instance. This attribute may be set via the FLUX_CONF_DIR environment variable, or the flux-broker(1) --config-path command line argument. Default: none. See also flux-config(5).


tbon.topo [Updates: C]

URI describing the TBON tree topology such as kary:16. The kary scheme selects a complete, k-ary tree with fanout k, with kary:0 meaning that rank 0 is the parent of all other ranks by convention. The binomial scheme selects a binomial tree topology of the minimum order that fits the instance size. Default: kary:2, unless bootstrapping by TOML configuration, then see flux-config-bootstrap(5).


Number of descendants "below" this node of the tree based overlay network, not including this node.


The level of this node in the tree based overlay network. Root is level 0.


The maximum level number in the tree based overlay network. Maxlevel is 0 for a size=1 instance.


The ZeroMQ endpoint of this broker's TBON parent.

tbon.zmqdebug [Updates: C]

If set to an non-zero integer value, 0MQ socket event logging is enabled, if available. This is potentially useful for debugging overlay connectivity problems. Default: 0.

tbon.prefertcp [Updates: C]

If set to an integer value other than zero, and the broker is bootstrapping with PMI, tcp:// endpoints will be used instead of ipc://, even if all brokers are on a single node. Default: 0.

tbon.torpid_min [Updates: C, R]

The amount of time (in RFC 23 Flux Standard Duration format) that a broker will allow the connection to its TBON parent to remain idle before sending a control message to indicate create activity. Default: 5s.

tbon.torpid_max [Updates: C, R]

The amount of time (in RFC 23 Flux Standard Duration format) that a broker will wait for an idle TBON child connection to send messages before declaring it torpid (unresponsive). A value of 0 disables torpid node checking. Torpid nodes are automatically drained and require manual undraining with flux-resource(1). Default: 30s.


The amount of time (in RFC 23 Flux Standard Duration format) that a broker waits for a TBON child connection to acknowledge transmitted TCP data before forcibly closing the connection. A value of 0 means use the system default. This value affects how Flux responds to an abruptly turned off node, which could take up to 20m if this value is not set. This attribute may not be changed during runtime. The broker attribute overrides the flux-config-tbon(5) tcp_user_timeout value, if configured. See also: tcp(7), TCP_USER_TIMEOUT socket option.


log-ring-size [Updates: C, R]

The maximum number of log entries that can be stored in the ring buffer. Default: 1024.

log-forward-level [Updates: C, R]

Log entries at syslog(3) level at or below this value are forwarded to rank zero for permanent capture. Default 7 (LOG_DEBUG).

log-critical-level [Updates: C, R]

Log entries at syslog(3) level at or below this value are copied to stderr on the logging rank, for capture by the enclosing instance. Default 2 (LOG_CRIT).

log-filename [Updates: C, R]

(rank zero only) If set, session log entries, as filtered by log-forward-level, are directed to this file. Default: none.

log-stderr-mode [Updates: C, R]

If set to "leader" (default), broker rank 0 emits forwarded logs from other ranks to stderr, subject to the constraints of log-forward-level and log-stderr-level. If set to "local", each broker emits its own logs to stderr, subject to the constraints of log-stderr-level. Default: leader.

log-stderr-level (Updates: C, R)

Log entries at syslog(3) level at or below this value to stderr, subject to log-stderr-mode. Default: 3 (LOG_ERR).

log-level (Updates: C, R)

Log entries at syslog(3) level at or below this value are stored in the ring buffer. Default: 7 (LOG_DEBUG).


content.backing-module (Updates: C)

The selected backing store module, if any. This attribute is only set on rank 0 where the content backing store is active. Default: content-sqlite.

content.blob-size-limit (Updates: C, R)

The maximum size of a blob, the basic unit of content storage. Default: 1073741824.

content.flush-batch-limit (Updates: C, R)

The maximum number of outstanding store requests that will be initiated when handling a flush or backing store load operation. Default: 256.

content.hash (Updates: C)

The selected hash algorithm. Default sha1. Other options: sha256.

content.purge-old-entry (Updates: C, R)

When the cache size footprint needs to be reduced, only consider purging entries that are older than this number of seconds. Default: 10.

content.purge-target-size (Updates: C, R)

If possible, the cache size purged periodically so that the total size of the cache stays at or below this value, in bytes. Default: 16777216.


Flux: http://flux-framework.org

RFC 13: Simple Process Manager Interface v1: https://flux-framework.readthedocs.io/projects/flux-rfc/en/latest/spec_13.html

RFC 22: Idset String Representation: https://flux-framework.readthedocs.io/projects/flux-rfc/en/latest/spec_22.html

RFC 23: Flux Standard Duration: https://flux-framework.readthedocs.io/projects/flux-rfc/en/latest/spec_23.html

RFC 29: Hostlist Format: https://flux-framework.readthedocs.io/projects/flux-rfc/en/latest/spec_29.html


flux-broker(1), flux-getattr(1), flux_attr_get(3)