Re: Kill Power vs. Clean Shutdown
poweroff -f handles the syncing of the filesystems, should they be
unmounted. -f ignores
all of the init.d scripts, but does not ignore flushing of any
filesystems that may be mounted.
( -n does that ). I'm not sure if it will mark filesystems as
'unmounted', but I believe it should
(unless someone informs me otherwise), at the very least, mark the
filesystems as 'clean'.
Shane Geiger wrote:
DON'T DO SHUTDOWN OR HALT UNLESS YOU HAVE TO--AND YOU RARELY DO. :-)
This makes little sense on a Live CD, and it takes too much time. You
could power off the machine, but what happens if you forget to unmount
The safe way to quickly shut down a live CD-booted machine or one
running from the hard drive is to use the magic sysrq functionality
(if it's in your kernel).
On a laptop, I often use alt-sysrq (since I don't have any network
services running from it or any databases). You can also use
alt-sysrq on a machine that has frozen--it's a much safer alternative
to cutting the power to the machine.
If you enabled Magic SysRq (CONFIG_MAGIC_SYSRQ=y, found in make
menuconfig at Kernel hacking -> Kernel debugging -> Magic SysRq key)
in your kernel you can cleanly reboot if evil freezes your system with
the following keyboard combination:
1. Alt-SysRq-R (keyboard in raw mode)
2. Alt-SysRq-S (save unsaved data to disk)
3. Alt-SysRq-E (send termination signal)
4. Alt-SysRq-I (send kill signal)
5. Alt-SysRq-U (remount all mounted file systems)
-- SHANE: IS THAT REMOUNTING OR UNMOUNTING??? I THINK
THAT'S AN ERROR.
6. Alt-SysRq-B (reboots the system)
Alt+SysRq+e - try to nicely kill processes
(wait a little bit here)
Alt+SysRq+i - no more mister nice guy
Alt+SysRq+s - sync the disk
Alt+SysRq+u - unmount disks
(wait a bit here, too)
Alt+SysRq+b - reboot
It's better to Sync AFTER killing your processes, just before
unmounting the filesystems, so a safter sequence would be E-I-S-U-B.
And you can even have fun with the acronym; "Everything Is Super,
If you find that holding three keys is difficult, you do have some
other choices. You can trigger it manually:
echo t > /proc/sysrq-trigger
Or, you can make the Alt-SysRq "sticky" by:
echo 1 > sysrq-sticky
With that done, you can hold Alt-SysRq, release it, and then leisurely
press "t" or whatever key you wanted.
You could also change the SysRq itself in /proc/sys/kernel/sysrq-key
(it's normally 84 - Alt-SysRq for Intel).
If you are trying to do this sort of thing from a script, you can do
something like this:
sudo su -c 'echo e > /proc/sysrq-trigger; sleep 3; echo i >
/proc/sysrq-trigger; echo s > /proc/sysrq-trigger; echo u >
/proc/sysrq-trigger; sleep 3; echo b > /proc/sysrq-trigger'
# Note: I'm not sure why the sleep statements are needed. But, rest
assured, this gets the job done.
Stephen Samuel wrote:
Depends on whether or not you have swap. If you do, there is a SMALL
possibility that you could power down during a write to the swap
artition and that you would get a spurious write that could trash the
partition data -- or even real data.
I usually use ''poweroff -f' It takes all of about 3-10 seconds with
Knoppix 5.0.1, and ensures that there
are no spurious writes.
Tim Ross wrote:
If you're running the Live CD and don't have any external devices
mounted, can you power the machine down with the on/off button
rather than do a clean shutdown without hurting anything?
Since we're dealing with a RAM disk, I'd think nothing would get
"hurt" by killing the power (and it would be faster)...
Stephen Samuel +1(778)861-7641 firstname.lastname@example.org
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