I have recently faced this issue when I was setting up my Splunk server on a remote machine.
Sometimes it happens that the port you want to use is already in use by other service or it is not available to the user which you are using to start Splunk. In that case, you either need to change the port or the user.
There is not much of a setting you need to change, you can use the following ways to change the mgmt port,
1. Change the management port using CLI,
splunk set splunkd-port 9089
Source:
https://docs.splunk.com/Documentation/Splunk/7.2.6/Admin/Changedefaultvalues
2. Change the management port by updating the configuration file(web.conf),
You will find the below line in the conf file and update it with the port of your choice,
mgmtHostPort = 127.0.0.1:9089
Hope it helps!
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