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I have a small powershell script which allows me to quickly set an alarm for myself. It basically just waits a specified number of minutes and then calls

msg * alarm!

This works well - a message box pops up. The only problem is it disappears after a while - so if I'm not at my desk, I'll miss the message box.

According to the documentation, found here, this is the behaviour when I don't specify a time value.

/time: seconds : Specifies the amount of time the message you sent is displayed on the user's screen. Once the time limit is reached, the message disappears. If no time limit is set, the message remains on the user's screen until the user sees the message and clicks OK.

However this isn't the case and it does disappear. Right now, I have to specify an arbitarily high number for it to stay.

    msg * /time:999999 alarm!
Lieven Keersmaekers
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Diskdrive
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    ok can someone explain this why this is a bad question? – Diskdrive Nov 07 '16 at 02:34
  • It is not a programming/development question. It is a question about the behavior of a Windows system utility. – Bill_Stewart Nov 07 '16 at 02:42
  • @Bill_Stewart - really? questions regarding command line commands are out of scope for this site now? There's literally a tag for this and this question has like 300+ upvotes (http://stackoverflow.com/questions/8055371/how-to-run-two-commands-in-one-line-in-windows-cmd) – Diskdrive Nov 07 '16 at 02:52
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    I didn't downvote; it was just a guess on my part. – Bill_Stewart Nov 07 '16 at 02:54
  • I guess something is wrong with the timer in the script... – Efi Nov 07 '16 at 06:45
  • @andlabs - Whatever shell you use to start msg will result in the same behavior. This is definitely not powershell related, just msg.exe related. The winapi tag is debatable though. Perhaps a Windows Internals tag is needed. – Lieven Keersmaekers Nov 07 '16 at 19:57
  • @LievenKeersmaekers oh, `msg` is not a PowerShell command? Good to know; thanks – andlabs Nov 07 '16 at 20:05

2 Answers2

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Tracing the call's with cdb shows following function of interest when starting msg.exe and passing it the maximum timeout value of 999999:

command: msg * /time:999999 alarm

The timeout value of f423f (999999) gets passed to ShowMessageBox through the rax register.

WINSTA!WinStationSendMessageW+0x353:
000007fe`fbf1ec93 e874deffff      
call    WINSTA!CSmartSession::ShowMessageBox (000007fe`fbf1cb0c)
rax=00000000000f423f rbx=0000000000000000 rcx=0000000000000010

Starting msg.exe without any timeout value shows 3c (60) being passed to the ShowMessageBox function.

command: msg * alarm

WINSTA!WinStationSendMessageW+0x353:
000007fe`fbf1ec93 e874deffff      
call    WINSTA!CSmartSession::ShowMessageBox (000007fe`fbf1cb0c)
rax=000000000000003c rbx=0000000000000000 rcx=0000000000000010

My guess is that the documentation is not up-to-date (if it ever was)

Lieven Keersmaekers
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  • Hi Lieven - just wondering, what is this cdb command that you're using to trace? – Diskdrive Nov 09 '16 at 22:19
  • I used this one `cdb -c ".while (1) {tc;r}" msg.exe * /time:999999 alarm >> msgtrace.txt` and it did the job but I'm sure it can be optimized in many ways. The while loop should not be necessary for instance, I had to kill the debugger at the end because of the while loop, ... – Lieven Keersmaekers Nov 10 '16 at 06:01
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try/time:0, works for me, but waited for several minutes only

Paweł Motylski
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