Now I have a new observation and am seeking comments.
I am using XP Pro SP3 and was experimenting with some things and ran chkdsk /r and responded in the affirmative to have it run on the next reboot.
I rebooted and pressed the any key to abort the chkdsk and all is well.
I scheduled another chkdsk /r, responded in the affirmative and rebooted except this time I chose Safe Mode with Networking to see if I would get a chance to press the any key to abort the chkdsk (this was my experiment).
Well, Safe Mode rolls along and gets to mup.sys and then the system "hangs" (you know what I mean...it appears to hang), but my HDD light is flashing, so I figure it is running the scheduled chkdsk /r and I wait - a long time, about 45 minutes with mup.sys sitting on the screen. If I did not know that chkdsk was running, I would have thought I had some other problem after just a few minutes and started pressing the reset button and troubleshooting something else.
After about 45 minutes of HDD flashing, chkdsk apparently completes, the system reboots (in Normal mode even though I chose Safe Mode before) and the chkdsk results are in the Event Log as they should be.
I then used fsutil to mark my volume dirty and rebooted in Safe Mode again and autocheck ran chkdsk for me as expected and the system still appeared to be hung on mup.sys for another long time until the chkdsk completed (since the volume was dirty) and rebooted normally logging the event.
My thinking is that now I have another question or two to ask when somebody says their system is hung on mup.sys... Of course it is not really ever hung on mup.sys (it is what comes after it).
Did they sometime recently run chkdsk /r and then try to boot in Safe Mode in their troubleshooting effort? If yes, then you can expect it to sit there on mup.sys for a long time.
Could the system really just be be running chkdsk and you may have to wait a long time for it to finish?
Depending on what chkdsk /r finds to do, the last thing you see on the screen in Safe Mode could be mup.sys for a long time, when in fact everything is fine.
If chkdsk fails to clear the dirty bit, you will never get past mup.sys and of course have to come up with some other way (Recovery Console) to run chkdsk /r or do some other troubleshooting, etc.
Maybe this is all obvious and everybody knows it already, but I have never seen it and now I can think of another reason why a system booting in Safe Mode might appear to hang on mup.sys "forever" - it is running chkdsk /r like you told it to.
Perhaps some brave soul will give this experiment a shot and make sure I am not off in the weeds
Edited by joseibarra, 04 August 2010 - 06:50 PM.