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Identifying the source of SQL Server login failures (18456 errors)

We’ve all had to isolate the source of login failures from time to time, and thanks to a distinct lack of information presented in the SQL Server error log about these login failures it’s not as straightforward as it could be (although this is improving with each release of SQL Server).

However, with a little help from SQL Server’s tracing tools it’s not too difficult to get to the bottom of these login failures.

The technique is pretty much version independent, but I will assume you know how to use SQL Server Profiler and capture a trace.

Login Error 18456

A login failure will throw an 18456 error and will be accompanied by the following entry in the SQL Server error log (SQL Server 2000 does not display the IP address):

2009-01-15 09:40:24.55 Logon Error: 18456, Severity: 14, State: 8.
2009-01-15 09:40:24.55 Logon Login failed for user 'Domain\User'. [CLIENT: xxx.xxx.xxx.xxx]

The severity of the error indicates the seriousness of the error. A severity level of 14 indicates an error in the range described as user correctable, which is understandable for login failures.

The next item of information the error provides is the state number. Most errors have a state number associated with them which provides further information which is usually unique to the error that has been thrown. For a login error, state: 8, shown in the above example, indicates an invalid password was used.

The state number therefore provides invaluable information about the reason for the login failure and can often be enough to identify the cause of an 18456 error.

The table below illustrates what some of these state values mean:

State Error description
1 Account is locked out
2 User id is not valid
3-4 Undocumented
5 User id is not valid
6 Undocumented
7 The login being used is disabled
8 Incorrect password
9 Invalid password
10 Related to a SQL login being bound to Windows domain password policy enforcement. See KB925744.
11-12 Login valid but server access failed
16 Login valid, but not permissioned to use the target database
18 Password expired
27 Initial database could not be found
38 Login valid but database unavailable (or login not permissioned)

The next item of information is the login (SQL Server or Windows) generating the failure, followed by the IP address of the host from which the login was attempted, which provides a useful cross-reference to confirm we’re looking at the right host when we’re trying to isolate the login failure.

Isolating the login failure

If the information provided in the error log for the login failure is not enough to isolate the source of the errors, the next step is to run a quick trace against SQL Server to get more information.
The easiest way to identify the process generating the login failures is via a SQL Server Profiler (SSP) trace.

If you’re running SQL Server 2005 or above and you still have the default trace enabled (which is on by default in an out-of-the-box installation) then you don’t need to start a new trace; check out my SQL Server default trace post instead.

If the default trace is disabled, or you have an earlier version of SQL Server, then read on.

Start SSP, and, using either your favourite trace template, or via a new trace template (File > Templates > New Templates…) make sure the following columns are selected:

  • ClientProcessID
  • Hostname
  • LoginName
  • NTUserName
  • NTDomainName
  • ApplicationName

These columns can be found in the Trace Properties dialog on the Events Selection tab. If they are not visible, tick the Show all columns checkbox. Note that SPID is always a selected column by default, and cannot be de-selected.
(Edit: Adding StartTime to the list may be useful here in order to help isolate login failures that only occur at certain times).

Under Events select the Audit Login Failed event under Security Audit ([EDIT] and under Errors and Warnings select User Error Messages as JJ has reminded me below, otherwise we don’t see the name of the database that the login failed against).
As we’re only interested in login failures these are the only events we need, and will help ensure that any performance impact from running the trace can be kept to a minimum. On a production system it’s never really advisable (imho) to run a graphical SSP trace on the server; always use a server side trace (although I must admit I’ve fallen off my high horse on that front more than once).

Figure 1 below shows a completed trace template:

Fig. 1: Completed SQL Server login failure trace template

It might look a bit sparse, but we are only interested in a specific error.

Step 1
Save the modified trace template and launch a new trace, specifying the saved template as the template for the new trace and wait for the login failures. Stop the trace after a login failure has been generated.

Step 2
The Hostname column should have recorded the name of the server that the invalid login emanated from and the ClientProcessID should have captured the Process ID, or PID of the offending process (or processes if there are multiple processes involved).

Step 3
Log on to the server triggering the errors, and list the PIDs of the relevant processes. This can be done using Tasklist or Task Manager.

To view the PIDs via Task Manager, start Task Manager (Shift+Ctrl+Esc), go to View > Select Columns… and tick the checkbox labelled PID (Process Identifier) and click OK.

Figure 1 below shows a completed trace template:
Fig. 2: Task Manager

Click on the Processes tab to bring all the processes running on that server into view (make sure Show all processes from all users is ticked) and click on the PID column heading to sort the PIDs in descending or ascending order.

Step 4
Once you’ve isolated the process responsible via the PID it should just be a matter of identifying where that process stores the credentials it uses for logging into SQL Server and verifying them.
Usually, the process will be a service, so it’s just a question of bringing up the Services plugin via Control Panel, or Start > Run > services.msc should also do the trick.

That’s it, so happy hunting!

Useful links

Troubleshooting: Login failed for user ‘x’
Understanding “login failed” (Error 18456) error messages in SQL Server 2005

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This entry was posted on Friday, January 23rd, 2009 at 2:07 pm and is filed under SQL Server. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

22 Responses to “Identifying the source of SQL Server login failures (18456 errors)”

  1. Daily Blog List - Kev's Life Says:
    June 22nd, 2009 at 2:10 am

    [...] Identifying the source of SQL Server login failures (18456 errors) [...]

  2. Michael Says:
    June 25th, 2009 at 4:07 pm

    THANK YOU!!! I have been searching days to resolve this error and your instructions worked wonders for me!!!!

  3. Jason TEPOORTEN Says:
    July 15th, 2009 at 2:43 am

    Hi.

    Thank you VERY much for making the effort of leaving a well-written and easy to follow article.

    It helped me isolated a login failure on our MS-SQL 2000 server that was occurring every second.

    Kind Regards,

    Jason

  4. Rick Morgan Says:
    June 6th, 2010 at 12:10 am

    Very informative and helpful – save me from utter frustration. Thanks for the work.

  5. Larry Says:
    December 23rd, 2010 at 12:22 pm

    Thank you, it helped me find the cause to my login error i had for month. Very well written.

  6. The SQL Server Default Trace Says:
    February 21st, 2011 at 7:46 pm

    [...] The query references the trace file from the period of the login failure and retrieves the columns containing all the information that should be needed to pin down where any login failure recorded in that file came from. I’ve already covered how to use this information in another blog posting covering how to identify the source of login failures. [...]

  7. Margaret Says:
    March 3rd, 2011 at 12:59 pm

    Best description of troubleshooting login errors that I’ve seen on the web – nicely done!

  8. Chris Says:
    March 22nd, 2011 at 6:17 pm

    Hi,

    This is the best description I’ve found so far on how to identify failures. It’s helped me to find out quite a bit after I got done with a SQL server migration where we trimmed databases which supposedly were not in use.

    One question: Is there a way to tell what non-existent database a particular login is requesting?

    I have an unknown web-based app that is triggerred by an unknown individual which I can’t predict when it’ll happen next, so continually using SSP would seem to be taxing if run for a number of days waiting for that to happen. If I could just find out what database the user or process is trying to request, that might clue me in to what application is requesting the non-existent database to either obsolete the app or bring back online the database.

    Currently, I’m using alerts which tell me when the event happened, what the login and client IP is and the error, “Failed to open the explicitly specified database”. The

    Thanks in advance for any tips or advice!

    -Chris

  9. Ajmer Dhariwal Says:
    March 22nd, 2011 at 10:08 pm

    Hi Chris,

    This is a bit of a flaw in the current setup as the database engine knows everything (the client process id, hostname, db name the login is trying to use etc etc) but the error messages do not include all the pertinent information (for what it’s worth, it’s being addressed in the next version: http://connect.microsoft.com/SQLServer/feedback/details/590004/add-database-name-to-error-18456-message).
    The good news is that the login is still there, otherwise you’d get a different error, so I’d suggest that the you check the properties for that login in SSMS and view the default database that login is associated with – this should identify the db in question.
    If the default database is master, or some other valid database then the process in question must be specifying an alternate name in the connection string it is using to connect, so you’ll have to identify where this proc is storing that info – normally the trace identifies the hostname and process pid which should help.
    You can use SSP to save the trace template as a file and run it as a server side trace which will have minimal impact on the server (File > Export > Script Trace Definition…) and control it via sp_trace_setstatus.

    Good luck!

  10. Rob Says:
    May 20th, 2011 at 10:06 am

    Great clearly written article , it helped me find the cause of a login error i had for months.

    Thanks

  11. JJ Says:
    May 27th, 2011 at 9:48 pm

    Hi Chris, Hi Ajmer,

    for me works following to get the databasename:
    You can trace requested databasename with profiler, you must select “User Error Message” under “Errors and Warnings”! So add this Event to your trace template beside “Audit Login Failed”

    If your trace is active and the login error occurs you will see a message like:
    Then you will se textdata like “Cannot open database “XYZ” requested by the login. The login failed

  12. Ajmer Dhariwal Says:
    June 13th, 2011 at 9:01 pm

    Good point JJ – something I’d entirely forgotten in my hurry to keep the profiler template as light as possible.

  13. Myra Rosa Says:
    July 8th, 2011 at 11:44 pm

    Thank you! This is very helpful. You have some excellent SQL Karma coming your way :)

  14. Ozie Says:
    July 19th, 2011 at 5:02 pm

    Thank you for pointing me in the right direction

  15. Deb Says:
    August 12th, 2011 at 9:34 pm

    I was getting those mysterious Error: 18456, Severity: 14, State: 38. messages every three minutes on one of my test servers, and this helped me pinpoint the db name and the client process that was trying to access it. I had suspected it was a database we recently migrated to a production server, and the application support person was arguing it couldn’t be, he had changed all the pointers. This solved the argument quickly and finally.

    Thanks very much for posting this info.

  16. Crystal Reports Generating SQL Server Error 18456 Severity 8 Error Logs « Justin Cooney – Senior Programmer / Analyst Says:
    October 3rd, 2011 at 6:42 pm

    [...] Identifying the source of SQL Server login failures (18456 errors) Share this:TwitterLike this:LikeBe the first to like this post. [...]

  17. Diane Says:
    November 2nd, 2011 at 5:06 pm

    Thank you for the information. This has been somewhat helpful, at least more so than other articles I have found. I am having one issue though. The trace is capturing the information but it goes by so fast I can’t catch the PID on task manager when it’s caught in profiler. Is there anything I can do to see this? I don’t know what process is running to cause failure and that is what I am trying to catch. Please advise.

    Much thanks!!!

  18. Ajmer Dhariwal Says:
    November 3rd, 2011 at 6:43 pm

    The trace can be stopped or paused and saved so you can go back over it in your own time.
    You can capture a similar trace of the processes and their PIDs by running an e.g. perfmon trace, or you can just open a DOS prompt (command window) on the host sending the invalid logins and typing “tasklist” and hitting return.
    This will list all the processes running on that host along with their PIDs which you can then reconcile with the trace output. You can also redirect the tasklist output to file via “tasklist > c:\temp\tasks.txt”. If you use the following syntax with “tasklist >> c:\temp\tasks.txt” you can append the output to a text file, which means you can repeatedly run the tasklist command on a scheduled basis, for example, and this will allow you to capture all the processes and their PIDs over the time interval you schedule it for. With the trace and tasklist data saved you can go over it at your lesiure to reconcile the logins with their PIDs.

  19. Ashish Jain Says:
    November 25th, 2011 at 9:49 am

    Very important and nicely written post

  20. philip Says:
    December 9th, 2011 at 4:55 pm

    awsome article, it allowed me to find the process and the service but i’m still getting the lock outs. they are happening on the master database of our sql1/sql1 instance. the process is sqlagent90.exe and the service is SQL Server(sql1) i have verified that the account running the service is correct, i have verified that the service account is in the security folder of the master database.

    our sql enviorment is in a MS cluster. this failure aduit is only happening on this node of the cluster. i’m lost as to what to do now.

  21. Ajmer Dhariwal Says:
    December 10th, 2011 at 6:56 pm

    This is the sql server agent account and it sounds like the account is locked out or disabled in some way.
    From a dos prompt run “net user /domain” where is the full service account name (including domain name) and check the Account Active status and there is no password expiry for the account.
    If that doesn’t help then send me the full fragment from the error log showing the login failure.

  22. Anonymous Says:
    December 27th, 2011 at 9:49 pm

    Searched for hours until coming across this entry — great article! Thank you for sharing!

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