In Splunk Enterprise, you can customize the Splunk platform login page with plain or HTML formatted text. Custom text will be added in web.conf file.
so first step is locate the web.conf file. Follow the path $SPLUNK_HOME/etc/system/local/ directory.
first check if web.conf file exists or not. if not then create a one in the directory local under system directory.
step1) once you locate or created the web.conf file locate or create stanza
step2) add or edit the login_content string under the [settings] stanza.
Ensure that the text and formatting are no longer than one line in the configuration file.
step3) and last step is to restart your splunk because whenever you make any changes in any conf file you have to restart your splunk. so that changes reflect.
example:
copy from https://github.com/splunkgeeks/splunk_admin/
