# $SYS - System Topic

The EMQX Broker periodically publishes its running status, message statistics, client online and offline events to the system topic starting with $SYS/.

The $SYS topic path begins with $SYS/brokers/{node}/. {node} is the name of the node where the event/message is generated, for example:

$SYS/brokers/emqx@127.0.0.1/version
$SYS/brokers/emqx@127.0.0.1/uptime
 
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$SYS system message publish interval is configured in etc/emqx.conf:

broker.sys_interval = 1m
 
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# Cluster status information

# Client Online and Offline Events

$SYS topic prefix: $SYS/brokers/${node}/clients/

The Payload of the ‘connected’ event message can be parsed into JSON format:

{
    "username": "foo",
    "ts": 1625572213873,
    "sockport": 1883,
    "proto_ver": 4,
    "proto_name": "MQTT",
    "keepalive": 60,
    "ipaddress": "127.0.0.1",
    "expiry_interval": 0,
    "connected_at": 1625572213873,
    "connack": 0,
    "clientid": "emqtt-8348fe27a87976ad4db3",
    "clean_start": true
}
 
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The Payload of the ‘disconnected’ event message can be parsed into JSON format:

{
    "username": "foo",
    "ts": 1625572213873,
    "sockport": 1883,
    "reason": "tcp_closed",
    "proto_ver": 4,
    "proto_name": "MQTT",
    "ipaddress": "127.0.0.1",
    "disconnected_at": 1625572213873,
    "clientid": "emqtt-8348fe27a87976ad4db3"
}
 
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# Statistics

System topic prefix : $SYS/brokers/${node}/stats/

# Client statistics

# Subscription statistics

# Topic statistics

# Routes statistics

The topics.count and topics.max are numerically equal to routes.count and routes.max.

# Throughput (bytes/packets/message) statistics

System Topic Prefix : $SYS/brokers/${node}/metrics/

# sent and received bytes statistics

# sent and received MQTT packets statistics

# MQTT sent and received messages statistics

# Alarms - system alarms

System Topic Prefix: $SYS/brokers/${node}/alarms/

# Sysmon - system monitoring

System Topic Prefix: $SYS/brokers/${node}/sysmon/