I while ago I was tasked with the responsibility of setting up our SharePoint Foundation 2010 server with the built in SharePoint Search functionality.
We created two accounts for this purpose. A spSearch to run the service and spCrawl to crawl the content DBs. I setup the Foundation Search service with the spSearch account as the service account, the spCrawl account with pwd was added to the Content Access Acount. The database was added (no specific instance required) and the database left at default settings. I updated the index timings and clicked ok.
I then clicked on the start link and clicked again on the start button. I ensured the crawl account had access to the content database and added the server running search to the content database.
As near as I can tell none of the accounts are setup with any special rights or restrictions.
Once the search functionality was initiated we started to receive the following errors in our Windows server logs:
Log Name: Application
Source: Microsoft-SharePoint Products-SharePoint Foundation Search
Date: 8/15/2012 3:11:53 PM
Event ID: 57
Task Category: Search service
Description: A database error occurred. Source: Microsoft OLE DB Provider for SQL Server Code: 14 occurred 257 time(s) Description: [DBNETLIB][ConnectionOpen (Invalid Instance()).]Invalid connection.
Turns out it was simply a case of the new guy not knowing the infrastructure properly. The SQL instance for the SharePoint databases was not a default instance. I connected to the database server and found there was an instance labeled SharePoint that no one had told me about. I corrected the database settings for the search service and this resolved the issue. I also could have corrected this without going to the server itself, by checking the Content Database settings in Central Admin. Oh well, new experience I hope to have learned from my mistake.