C# Windows Service Textwriter

Question

I've created a standard windows service that uses the LocalSystem account. For the log files I use textwriter to write to a specified file within C:\Users\useraccount directory. The problem is, when running as a service under LocalSystem, it doesn't want to create or write to the file at all.

 string dir = @"C:\Users\useraccount\log.txt";
 StreamWriter sw = File.AppendText(dir);

As you can see, the directory is hardcoded in so there isn't any base directory conflicts seeing as LocalSystem would start in System32 or something of that nature. The permissions on the folder lets the System account access it fully (windows 7) so why am I not able to create/write to that file?

Thanks for any input!

Edit:

Apparently the logging program thread is running as LocalSystem as well, when I really need it to be running as a standard user. So how do I execute a threaded process from the service to run under the local user account instead of under LocalSystem.

I use Thread.new(process) where process is an additional program. The process program needs to receive input before it writes anything, and it isn't receiving input because it's on the wrong account. How would I fix this?

Answer 1

Try this code and check what exception reports:

try
{
     using (StreamWriter sw = File.AppendText(dir))
     {
          sw.WriteLine("test");
     }
}
catch (Exception ex)
{
     Debug.Print(ex.Message);
}

Just a note: it's a good idea to use using(...) with all classes implementing IDisposable interface, so you can be sure they are freed when exiting block!

Answer 2

Should do the same trick as using(...) but did you try:

sw.Close();

Without it there's just an empty file but it throws no exceptions..

Answer 3

First of all I would use Log4Net instead of rolling your own logging mechanism, unless there is a good reason not to. This way you can create the log file you want but also (via a config or code) add log appenders such as windows event log. Then I would make sure I log any and all exceptions. You say no exception is being thrown, I expect there is an exception being thrown on the logging thread which is not 'bubbling' up, so catch it and log it (Log.Error(ex)). You can then see these exceptions in your event log if you have configured an event log appender.

Lastly, I'm not sure how you would assume the security context of the logged on user. Sounds like that would be a big securtity hole, unless you write something that prompts the user to enter their credentials or grant the process the right to impersonate/assume the user security context.. Perhaps that is the answer, the service responds to a user logon by prompting the user to grant this right. I'll have a look around for a better answer to this point.