Coral: cron srvstart utility: Difference between revisions

This short tutorial covers the SrvStart utility written by Nick Rozanski. It allows you to run a script as a service!  

A Windows Service is automatically started when your PC starts. Services automatically recover from program crashes and Standby or hibernation modes. Installing software as a Service requires Administrator permissions.

Programs (application) designed to run as a service contain code that interface to the Windows service manager. Running a script as a service requires additional code that allows it to access the Windows service manager. This code registers your script allowing it to be run as a service in addition it must provide responses to command requests from the service manager and have the ability to provide your scripts status.

Not a trivial exercise however this complexity is hidden when using SrvStart.  

We are interest only in files '''srvstart.exe''', '''srvstart.dll''' and '''logger.dll'''<br />

For this tutorial create a new folder c:\'''service_test''' and copy the above three files into it.

The documentation states copy files srvstart.exe, srvstart.dll, logger.dll and msvcrt.dll to C:\WINDOWS\system32 (system path). For XP onwards msvcrt.dll is already installed on a system path. Other three files need not be installed on a system path see below.

When installing a service it does write to the registry hence remember to stop and uninstall the service you create especially if running from a memory stick.  

This is an annoying VBScript it produces beeps when run.

 

Double click on my_script.vbs and confirm it produces two beeps.

An application to be run as a service must have one of the following file extensions .exe, .com or .bat The script we want to run has an extension .vbs hence cannot be run directly.

At first this looks very restrictive however a batch file will run any application.

To run our script as a service create a batch file named my_script.bat with the following content:

'''start''' Runs our vb script and closes. It does not wait for our vb script to finish<br />

'''Note 2:''' Removing the "start" keyword our vb script runs and the command window remains open until vb script finishes. Again when run as a service this is hidden.

We are now ready to install and run our service this can be done using a command prompt and issuing the appropriate commands.

Confirm two bleeps are produced. Note the following messages

With the confirmation of two beeps our script was successfully run. Reason for '''could not be started message'''; the batch file closes immediately when run. Srvstart regularly checks running status of an application it started, it immediately sees the script no longer running and reports back to the service control it could not be started.

The batch file is not running hence the service as reported is not running see above.

Above is not a problem its the way we want to run our scrip.

'''Note:''' The above results may be a little confusing, remember our VBScript does not run continuously its a run once program. Its purpose is to familiarise yourself with the Srvstart program.

* If cannot interact with the desktop.

Service start type specifies the services behavior after reboot:

We want our script to start when the PC is powered up. Either change the Manual state to Auto using service manger.

Alternatively use a script to set the service state. Create a new file named '''start_automatic.vbs''' with the following content:

For testing this script starts our service and changes it to Automatic.

'''Note 1:''' auto_restart will restart the service program if it exits for any reason. If restart_interval is defined, then before restarting, SRVSTART will wait seconds seconds.

'''Note 2:''' auto_restart does not; restart the service program if it is stopped by request (eg NET STOP or Control Panel|Services).

When Uniform Server is installed as a permanent installation concepts outlined above can be used for kicking portable cron into life.

Related to the above service is Uniform Server Cron both portable cron and running as a service have been implemented for details see [[Coral: cron intro|Cron]].