[ale] Kernel Parameters

[Chris Ricker]

On Tue, 13 Apr 1999, Glenn R. Stone wrote:

> Chris Ricker wrote:
> > 
> > Many of them are tunable via /proc.
> > 
> > eg,
> > 
> > cat /proc/foo/bar
> > 
> > to read it, and
> > 
> > echo "baz" > /proc/foo/bar
> > 
> > to change it.  But there's no integrated tool to see and change everything
> > beyond that.  If you're bored, writing one would be a good way to gain Linux
> > fame ;-).
> > 
> > For example, shmmax can be tuned like this.  Look at /proc/sys/kernel/shmmax
> > (at least with 2.2).
> 

> Is it just me, or is the idea of dynamic kernel tuning (a) unique to
> Linux and (b) just too cool for words?  Even on Slowlaris where you had
> the easy-edit file you hadda bounce the box...

Linux is the only Unix / Unix-like I've admin'ed where that much is tunable
on-the-fly, at least that I know of.  With FreeBSD, for example, not only
does changing things like SysV shared mem require an edit, it also requires
a recompile; at least Solaris doesn't do that ;-).  [I think; I've not yet
poked around in FreeBSD enough to be sure I've not just missed something]

That said, some stuff in Solaris is tunable on-the-fly.  You can use ndd to
control a lot of the TCP stack limits, for example.  Most of the rest isn't
because Sun claims that Solaris is self-tuning, and that you essentially
shouldn't have to change anything.

Conceptually at least, Solaris should be capable of doing more like Linux
than it does.  When you boot, /etc/system is parsed and then module settings
are adjusted from defaults according to that as they get linked into the
kernel.  I don't see why you shouldn't just be able to unload the module,
change an entry in the system file, and then relink the module back in....

In one way I prefer Solaris' behavior.  It's easier for me to
remember to do something like add

	panic_behavior:	1

to a system configuration file than it is for me to remember to add

	echo "1" > /proc/sys/kernel/panic

to rc.local.  But that's just me, and besides, I can easily emulate the
former on top of the latter by writing my own /etc/system file, then running
a script on bootup that parses that and echos stuff all over /proc, so I
don't constantly have to remember to do it myself.

 now it's like hey, database thrashing?  no
> problem, blip, have some more memory.  Now, if we could get this together with
> AIX's journalled file system..... (can you say, dynamic allocation of unused
> disk, dynamic re-optimization of logical space across physical volumes
> intrinsic to the OS/kernel, and all with live users on the system, and minimal
> performance hits?  talk about your killer app...)

I think Veritas or something like it is the "killer app" Linux needs to
totally dominate the small server market.

later,
chris

--
Chris Ricker                                               kaboom at gatech.edu
                                                  chris.ricker at m.cc.utah.edu