See the following docs page:
http://www.splunk.com/base/Documentation/latest/Admin/ConfigureSplunktostartatboottime
BTW, I do like to make a minor change to Splunk's default boot script that makes the startup work in a few extra situations. (For example, after a splunk upgrade)
By default, you'll see a line that looks like this (your's may be slightly different depending on what user splunkd is running as on your system, on mine the user is simply called "splunk"). This is in the splunk_start() function.
I change this line:
su splunk -c "\"$SPLUNK_HOME/bin/splunk\" start"
to the following:
su splunk -c "\"$SPLUNK_HOME/bin/splunk\" start --accept-license --answer-yes"
This ensures that any migration questions or license acceptance issues do not prevent splunk from starting up on an unattended boot. There are other startup options as well, but these are the two that I've found to work best for us.
