Thanks for the response. I've been using Macs for a little over four years now but this is only the first time I have gone to the system logs (or any of the other logs available from the consolute utility).
The system log appears to be completely unhelpful. I got up this morning sometime after 6:00 a.m. and posted my first report (see above) at 6:48 a.m. (I don't have a record of the exact times of the boot up freezes.)
Following are the *entire* contents ot the system log covering this period:
Nov 19 01:12:15 WHW-Mac-Mini loginwindow: loginwindow SleepWakeCallback WILL sleep
Nov 19 06:26:35 WHW-Mac-Mini loginwindow: loginwindow SleepWakeCallback will power on, Currenttime:11/19/2012 6:26:35.019 AM - Waketime:11/19/2012 6:26:33.980 AM = Deltatime:1.038853049
Nov 19 06:27:05 WHW-Mac-Mini loginwindow: no spins reported for this wake
Nov 19 07:35:13 WHW-Mac-Mini login: USER_PROCESS: 17714 ttys000
I assume that one of the two successful reboots that I did during this period was probably at 6:27.
The "all messages" log has some additional information from this time frame that may be useful:
11/19/12 6:26:35 AM kernel Wake reason = 11/19/12 6:26:35 AM kernel System Wake 11/19/12 6:26:35 AM kernel Previous Sleep Cause: 5 11/19/12 6:26:35 AM kernel EIR is supported. 11/19/12 6:26:35 AM kernel SSP is supported. 11/19/12 6:26:37 AM kernel AppleBCM5701Ethernet: 0 1 BJP firmware wakeup: service connect 11/19/12 6:26:37 AM kernel AppleBCM5701::selectMedium - autoselect, any duplex, flow control allowed 11/19/12 6:26:37 AM kernel Ethernet [AppleBCM5701Ethernet]: Link down on en0 11/19/12 6:26:38 AM kernel Ethernet [AppleBCM5701Ethernet]: Link up on en0, 1-Gigabit, Full-duplex, Symmetric flow-control, Debug [79ed,0f00,0de1,0300,c5e1,3c00] 11/19/12 6:26:39 AM ntpd bind() fd 25, family 30, port 123, scope 4, addr fe80::c62c:3ff:fe1f:4f7, in6_is_addr_multicast=0 flags=0x11 fails: Can't assign requested address 11/19/12 6:26:39 AM ntpd unable to create socket on en0 (17) for fe80::c62c:3ff:fe1f:4f7#123 11/19/12 6:26:40 AM configd network configuration changed. 11/19/12 6:26:43 AM /System/Library/CoreServices/RemoteManagement/AppleVNCServer.bundle/Contents/Mac OS/AppleVNCServer Authentication: FAILED :: User Name: N/A :: Viewer Address: 18.104.22.168 :: Type: VNC DES
Following this there were quite a few unsuccessful attempts to connect with my VNC server and little else that seemed noteworthy. Nothing that referenced anything to do with USB or USB peripherals.
And, of course, when I rebooted just now (in the hopes of getting a report from all of the logs corresponding to the exact time of the reboot), my Mini started just fine with no freeze up.
Next time you get a gray screen... with a bright light see what is going on in the screen.. (is a bit tricky to see, but works in a 45 degree angle).
Ya know, it's sounds related to this problem...
I wonder if it's a variation of this, of which I've seen many different symptoms...
Move the mouse or trackpad cursor over the center area of the login window so you can see the user icons. Click on the icon of the user that you would like to login as, type in the user's password, and press Return.
If the login window is configured to show only the name and password fields, type in the user's name and password into the fields, and press Return (even if you cannot see the rest of the login window).
This issue will not occur if the display is not sleeping when the account is logged out. Use the steps below to confirm that the account is not configured to log out automatically while the display is sleeping:
1. Open System Preferences > Security & Privacy > General. Click the padlock to unlock the preference pane and enter your admin password. Click the Advanced button at the bottom, then see if the option "Log out after N minutes of inactivity" (where N is the number of minutes) is enabled.
2. Open System Preferences > Energy Saver and configure Display Sleep to occur after the account is logged out, by dragging the slider to a number of minutes that is greater than N was set to in the previous step.
Important: If automatic log out is not needed, disable "Log out after Nminutes of inactivity" in System Preferences > Security & Privacy > General. This will also prevent the issue.
I am the only user; I have automatic login; I never log out or turn it off except when I shut it down to reboot. Of my six computers on the KVM, this is my day to day workhorse and the one computer that I usually leave the KVM set to. This means that having the display sleep is key to maintaining monitor life and saving energy. (My prior monitor-- a VX2835wm-- had never gone to sleep properly which was the subject of my one other thread at this site; my new monitor-- a Dell U2412M-- goes to sleep properly most of the time now which convinced me that my Mac Mini wasn't the cause of my earlier problem.) One of the many reasons I need to keep my computer running (and logged in) is that in addition to needing a live connection to my Apple TV, I also use the postfix server in the Unix portion of my Mac to send out log and report emails 24x7 from LAN side appliances such as a printer and an NAS device. So... I will try the trick with the bright light the next time there is a problem. I will also check to see if bypassing the KVM by attaching my Mac mouse and keyboard directly to the Mini's USB ports does anything... and I'll report back.
OK, so I had my Mac Mini freeze on the grey screen once again. I unplugged my USB cable and rebooted. Even though the USB cable was unplugged, the computer froze once again on the grey screen. This time, however, while the computer was frozen in front of me, I got interrupted by a phone call. While I was talking on the phone, after more than a minute or so had passed, I notice that a small grey circular picture of the earth appeared and that it flashed on and off several times for a minute or so at intervals a few seconds apart. Then that stopped and the normal boot up of the operating system happened. Because I was on the phone, I repeated the boot up process, this time with the USB cable to my KVM plugged in and this time with a digital camera present. I've attached a screenshot of the flashing image that I saw. (It was flashing fast enough that I only caught it once on two tries.)
Mea culpa: I now understand that this latest report was caused by my inadvertantly having turned on the network boot option. Given that I only discovered this feature five days ago when I was using my wife's Macbook (and subsequently checked it out on my Mac Mini at which time I must have changed the setting without realizing it), the two prior posts can be ignored but I am still searching for an answer to the USB related boot problem which I originally related. (In a way I am glad since this latest false flag was completely independent of whether or not my USB cable was plugged in which made the explanation suspect.) I apologize for not vetting my two prior posts more carefully but I jumped the gun in thinking that I had a recurrence of my original problem.