AndrC)s Delfino wrote: > What I'm trying to ask is this: if a user turns on the computer, and > can't log in, is it safe to power off the computer without using halt, > or shutdown, (ie. pressing the power off button)?
SHOULD you power down uncleanly? No. Can you? Usually. :) I would even go as far as to say, "almost always". If your machine is "busy", doing things that regularly write to disk, yeah, you really don't want to hit the power button. HOWEVER, if your machine is "idle" at the moment and you don't have an easy way to do a proper shut down, go ahead, hit the power button. FFS is pretty darned robust. It will cough and sputter a small amount on reboot, but it generally cleans itself up and comes up just fine. Will it do this EVERY time? Probably not. If you were in the middle of writing files, you can probably guess they are not-as-you-intended, and depending on what they were, you might be really upset about this. Or you might just say, "Whatever, get back to filtering packets for me, please", and never notice any "dammage" at all. The only time I can recall a system going down hard and not getting back up was when a SCSI card fell out of a machine with the power on (not a very interesting story -- IBM NetFinity 3000, for some unknown reason, they thought it was cute to HANG the cards umop apisdn in the machine...and I thought I'd be lazy and not put that annoying bracket in for this quick test. I think I was doing a cvs checkout (lots of writing), and the SCSI adapter fell out. File system was trashed, there. :) (hm. just recalled another time, which also, curiously, involved a CVS checkout...) IN FACT, on many occasions, I'll be too lazy to properly halt the machine (and wasn't going to need it immediately when it came back up) and just hit the power button. This is not how you want to run your machine normally, but stuff happens. I'd never want to put a really unstable file system, one that couldn't take an "oops!", into production. If it can take an "oops!", it can probably take a "deliberate" :) IF you anticipate the need for this, a few tips: make your partitions as small as possible (and extra space unused and unmounted) with as few files as possible, mount as many partitions RO (Read Only) as you can get away with for your application, try to minimize tasks that write to disk, and have a good backup. This will minimize the time the system spends doing an fsck on reboot...and the backup will save you when you want to kick my butt because you didn't notice all the qualifiers I put in this note. :) Not bad design principles, in general. I have set up a large archiving system -- the point is BIG and RELIABLE (or actually, repairable, without losing data), not super fast. It currently has around 1.8T of storage, and if maxed out with its current design (and current technology), about 4T of storage (all for about $5000US! I used to install 20M hard disks in machines for almost that much money! :). Storage is broken up into manageable chunks (about 300G at the moment, 500G if we were to max it out...much bigger, if we get the 1G physical disk limit overcome in OpenBSD). Trip over that power cord, we'll be waiting a while. HOWEVER, the design helps keep that manageable -- once a chunk is "filled", it is remounted read-only, and only one or two "reserve chunks" are kept read-write. Plus, the time critical stuff is kept on a smaller machine to keep the (re)boot times to a minimum. And yes, I yanked the power cord just to see what would happen (ans: after about 20 minutes to reboot, nothing exciting...though I was careful not to do this test during the hourly "fetch" cycle). So..in short: if you need to, go ahead, hit the button. Though if you can shut it down properly, please do so, that is always the prefered method. Nick.
