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SCCM reboot clients with random time-seed

Here is the goal: reboot more than 5.000 machines using SCCM at a given time. That's pretty easy when talking about servers or desktops. But my target are virtual computers, running on few physical clusters. I cannot simply reboot all of them at the same time since that could cause performance issues on these clusters when the VM's will come back online. The solution is obvious - add some random seed to the restart command.

Sure, they are some scripts to archive this goal, but I want to choose the simplest way - just to run BATCH command directly from distribution point.

The Windows CMD shell contains environmental variable %RANDOM% that generates random integer from 0 to 32767, so let's use it:

%SystemRoot%\system32\shutdown.exe /r /t %RANDOM% /d p:02:17

But this does not work in SCCM, why? Looks like that %RANDOM% variable is generated by cmd.exe process, so you can't simply run shutdown.exe with %RANDOM% variable in SCCM command line. The correct syntax is:

cmd.exe /c "%SystemRoot%\system32\shutdown.exe /r /t %RANDOM% /d p:02:17"

Time range:

One condition you need to acquiesce with is that this command reboots the computer in between 0 - 32767 seconds, or (32767 / 60 / 60) = 9.1 hours... 

How to hack default time range according your needs? The main idea is visible from this equation: ROUND( (%RANDOM%*MaxTimeToReboot) / 32767 )

Here is the equation converted to the batch code where the maximum time to reboot is 10 minutes (600 seconds): 

SET /a My_RND = (%RANDOM%*600/32767)

Putting all together:

The last step is to use %My_RND% variable instead of %RANDOM% in the shutdown command. Let's try:

cmd.exe /c "SET /a My_RND = (%RANDOM%*1000/32767) | %SystemRoot%\system32\shutdown.exe /r /t %My_RND% /d p:02:17"

Again, this does not work. And now it becomes somehow tricky, because some not well-know behavior of batch scripting comes in place.

Pipe:

commandA | commandB : Pipe the output from commandA into commandB

The issue why the pipe can not be used is because when a command is piped, everything behind the pipe is executed in a new instance of cmd.exe. And we have set the %My_RND% variable in the "first" instance, it's value is not defined in the new cmd.exe instance. Instead of pipe, I have used && redirection:

commandA && commandB : Run commandA, if it succeeds then run commandB

cmd.exe:

I need to solve two issues - run the cmd command and then terminate the cmd itself and force the cmd not to expand the %My_RND% variable at the time of parsing the whole command, but at the time of executing the shutdown command - because the variable is not defined when parsing the whole command. Take a look at the cmd.exe parameters:

Final batch command:

cmd.exe /v /c "SET /a My_RND = (%RANDOM%*600/32767) && %SystemRoot%\system32\shutdown.exe /r /t !My_RND! /d p:02:17"

Are you kidding me?:

On Windows 7 machine, list help for shutdown command and take a look at /t parameter:

10 years? Really does someone have a Windows 7 system running for 10 year's without reboot to utilize such a feature? :)

On Windows Server 2003 and 2008 (not R2) the /t parameter shows completely different situation:

 10 minutes? Really that is the maximum time-out period?

List of shutdown reasons:

/d parameter of the shutdown command, these reasons are displayed in eventlog.

(E = Expected U = Unexpected P = planned, C = customer defined)