I have upgraded Splunk enterprise from 6.4 to 6.5 version today.
I looking for a command to check when the last upgrade happened from 6.3 to 6.4 with date and time. I have old logs, but I couldn't find the details, and I am sure the upgrade happened from 6.3 to 6.4 two months back on my system. However, I can't get the version history.
Is there any other way to fetch the past version history?
_internal and _audit db retention policy is 30 days by default. So, probably you won't be able to find historical version change information from indexed data.
Otherwise, you can check splunkd.log or web_service.log for version info in general.
web_service.log (only if splunkweb is running. Indexers which disabled splunkweb cannot find this type of logs)
2016-10-12 16:04:28,259 INFO [57fec16e787f6c76b4fb90] root:650 - CONFIG: version_number (str): 6.5.0
splunkd.log (it is a build number)
10-12-2016 16:03:55.172 -0700 INFO loader - Splunkd starting (build 59c8927def0f).
Well then, if you're collecting basic logs on that system then this search might work (it worked for me):
index=main sourcetype="wineventlog:application" | rex field=_raw "(Splunk\sEnterprise\.\sProduct\sVersion:\s)(?<Splunk_Version>\d+\.\d+\.\d+\.\d+)" |dedup Splunk_Version,_time | table Splunk_Version,_time