why panic(9) ?

Chuck Swiger cswiger at mac.com
Tue Jan 11 21:43:50 UTC 2011

On Jan 11, 2011, at 1:11 PM, David DEMELIER wrote:
> 2011/1/11 Chuck Swiger <cswiger at mac.com>:
>> [ ... ]
>>> Yes, why this function exists? There is no way to solve a problem
>>> without panic'ing? Is panic really needed?
>> Sometimes, yes.  If it was possible for the kernel to handle an error condition without panic()ing, then that is obviously preferred-- but there are situations where there is no way for the system to recover.  Common examples of that include when the boot disk fails or disappears, or when the kernel runs out of memory in a situation where it can't get more free pages available.  Less common is when some kind of kernel invariant is violated, indicating that essential kernel data structures have been corrupted.
> Well I see, I know that kern.sync_on_panic exists to force a sync on a
> panic but because my laptop usually does not core dump so never reboot
> my disk are not sync'ed :-( it results in a file system not clean an
> that's the thing I really hate.

How often do you get panics?  I've got more FreeBSD systems that have never panic()ed in their operational lifespan than I've seen FreeBSD boxes which did panic, but most of the systems I deal with tend to be rack-mounted boxes in controlled datacenter environments.

Anyway, using a journaled filesystem would help.

>>> Seriously, I really hate when I play some music that suddenly the
>>> music get stucked in a infinite loop, why ?
>> Probably a bug in the sound card driver.
> No no, it was a panic that didn't core dump so I needed to do a hard reboot.

Frankly, audio isn't (or doesn't seem to be) a core goal of FreeBSD.  Macs are probably the best reference platform available for pro A/V work.  [1]

>>> I don't know because the panic does not core dump. But after some search I found that the panic
>>> was done because of conky. How the hell conky can panic FreeBSD?  We are in 2011 ! I think even Window 2000 does not crash on a user-land software.
>> "think"?  If you don't have experience running Windows 2000 are thus are simply guessing, let me assure you that Win 2000 can and does (or did) panic due to userland software.
> In fact I like FreeBSD, and I don't expect running anything else. But
> I must say that I didnt see windows 2000 crashing on my every boxes I
> have before switching to FreeBSD.

I didn't see Win2K crashing often, but certainly more often than once a year if the system was being used interactively.  On the other hand, I did see a Win2K database server running the Sybase-derived SQLServer platform in a data center, comparable to what I mentioned above, with a year-plus uptime.


[1]: Not just my opinion-- people who are/were recording engineers at studios back in the mid 90's and early 2000s widely used Avid's ProTools on the Mac.  More recently, the ready availability of consumer computing systems with the disk space and I/O bandwidth to do 12/18/more channel multitrack recording and editting in 24-bit by 48KHz or 96KHz has actually put a significant dent into pro studios, since people are doing a half-decent job of production work from their basement studio....

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