For checking the cluster master status from search peers or the search head run this command from web ui or the command line, (status will be described below 0/1 for the maintenance mode)
/opt/splunk/bin/splunk search "|rest /services/cluster/master/info"
Go to your cluster master and execute this command, '
./splunk show maintenance-mode
Maintenance mode : 0 indicates maintenance mode is OFF.
Maintenance mode : 1 indicates maintenance mode is ON.
login to your cluster master web UI and , settings -> index clustering, there you can see the status.
I'm on the cli of the indexer, not the cluster master. as indexers aren't search peers of the cluster master, the above rest command won't work. Thanks though.
Figured it out. Maintenance mode is listed as 0 (disabled) or 1 (enabled) in:
$ ./splunk list peer-info slave base_generation_id:345 is_registered:1 last_heartbeat_attempt:0 maintenance_mode:1 restart_state:NoRestart site:default status:Up