Nagios reports:

(Return code of 255 is out of bounds)

If you execute it from the command line you'll see something like:

[root@server]# ../../libexec/check_mssql_monitor -H sqlsvr -U DOMAIN\\user -P password -w 10 -c 20 --cpuWarning 200 --cpuCritical 400 --ioWarning 10 --ioCritical 20 -s

Unable to execute ms sp_monitor:Server message number=229 severity=14 state=5 line=1 server=SQL procedure=sp_monitor text=The EXECUTE permission was denied on the object 'sp_monitor', database 'mssqlsystemresource', schema 'sys'.

From reading this, it appears the user doesn't have permission to execute the stored procedure.

To quickly fix this in SQL Server 2005, I gave my user the ServerRole of 'sysadmin'. Probably not the most secure, but if you're isolated inside a DataCenter you are ok.

Ideally you would...