7 messages in org.freebsd.freebsd-currentRe: howto debug a complete hard reset| From | Sent On | Attachments |
|---|---|---|
| Alexander Best | Apr 13, 2012 2:36 pm | |
| O. Hartmann | Apr 13, 2012 3:40 pm | |
| Jeremie Le Hen | Apr 14, 2012 2:07 am | |
| Alexander Best | Apr 14, 2012 3:23 am |  .Other, .Other |
| Robert Huff | Apr 14, 2012 5:59 am | |
| Jeremie Le Hen | Apr 14, 2012 8:02 am | |
| Alexander Best | Apr 14, 2012 11:11 am |
| Subject: | Re: howto debug a complete hard reset | |
|---|---|---|
| From: | Alexander Best (arun...@freebsd.org) | |
| Date: | Apr 14, 2012 11:11:12 am | |
| List: | org.freebsd.freebsd-current | |
On Sat Apr 14 12, Jeremie Le Hen wrote:
On Sat, Apr 14, 2012 at 08:59:42AM -0400, Robert Huff wrote:
This is probably a sysctl handler that is causing the reboot. You can run this one-liner to spot the culprit (use sh):
for i in $(sysctl -Na); do sysctl $i >> ~/sysctl.out; sync; done
Each sysctl will be called in turn and the output is appended to a file, but the file will forcibly written to the disk before the next occurence.
Um ... it is my understanding sync(8) does not guarantee pending i/o will be written before it returns, but merely requests this happen irrespective of when it would normally occur. An I mistaken?
Honestly I don't know, but I have do admit that the small paragraph in the BUGS section of the sync(2) manpage is a little bit shivering:
BUGS The sync() system call may return before the buffers are completely flushed.
Can any enlightened person answer this?
sync(2) does REQUEST an immediate write to disk. however for this to actually be the case, one has to disable softupdates and disable the write cache of that particular disk. the write cache of hdds is enabled by default, because disabling it will give you a huge performance drop. there's a small section about this in tuning(7).
cheers. alex
ps: SU+J also mustn't be enabled for immediate writes to happen.
-- Jeremie Le Hen
Men are born free and equal. Later on, they're on their own. Jean Yanne
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