我使用mosquitto服务器作为mqtt经纪人 . 我测试mosquitto的性能，我需要为某些数据订阅$ SYS层次结构，例如当前从 $SYS/broker/clients/active 主题连接的数量 . 我有以下mosquitto配置文件 .
# Place your local configuration in /etc/mosquitto/conf.d/
#
# A full description of the configuration file is at
# /usr/share/doc/mosquitto/examples/mosquitto.conf.example
pid_file /var/run/mosquitto.pid
persistence true
persistence_location /var/lib/mosquitto/
log_dest file /var/log/mosquitto/mosquitto.log
include_dir /etc/mosquitto/conf.d
listener 1884
protocol websockets
listener 1883
sys_interval 1
max_connections -1
我正在订阅像这样的 $SYS/broker/clients/active 主题
ubuntu@linux-box:/etc/mosquitto$ mosquitto_sub -d -t $SYS/broker/clients/active
Client mosqsub/28715-ip-172-31 sending CONNECT
Client mosqsub/28715-ip-172-31 received CONNACK
Client mosqsub/28715-ip-172-31 sending SUBSCRIBE (Mid: 1, Topic: /broker/clients/active, QoS: 0)
Client mosqsub/28715-ip-172-31 received SUBACK
Subscribed (mid: 1): 0
配置文件中的 sys_interval 为1，但我没有收到上述订阅的任何更新 . 我也试过这个订阅一些替代主题，但仍然没有收到任何东西 . Mosquitto服务器托管在具有Linux操作系统的AWS微实例上 .
1 回答
$SYS被shell解释为环境变量，并且在mosquito_sub看到它之前被替换 . 您可以通过它在SUBSCRIBE日志语句中报告的主题字符串看到这种情况 .你应该在主题字符串周围加上引号：