[SunHELP] a question

velociraptor velociraptor at gmail.com
Fri Aug 27 14:12:47 CDT 2004

On Fri, 27 Aug 2004 10:26:07 -0400, Steve Rieger <steve at n2sw.com> wrote:
> Me think me wrote this yesterday but after working a 12 hour shift at the
> NYSE me forgets so here goes again
> Unix in general is is protected now in a very interesting way, if you run a
> process as any user (not UID 0) there is (I believe) 8% reserved, this 8%
> will not even whow up when using the df command, so for instance, if I had a
> 100 gig array and I run df I would see that my / only has 92 gigs capacity.
> No you don't lose the other 8% it is reserved for UID 0 just in case a proc
> fils up the slice, root will always be able to login. But keep in mind that
> (lets say) as user admin you run a " wget -m  www.cnn.com " and don't
> monitor it, you will fill up the partition that the pwd is in. once it is
> full apache will only run a single process the originating root process, and
> apache will not start any child processes to serve sites. No the server will
> probably not "crash" but only root will be able to initiate new connections.
> Once the slice is full if you type df -h you will see something similar to
> Filesystem            Size   Used  Avail Use% Mounted on
> /d0t0d1s0             114G   -6G   120G  100% /

You are referring to "minfree" reserved by mkfs when the partition is
created.  UFS (and other file systems) have provided minfree or
similar options for a while; it is not new.  Nor is it "protective"
other than giving the system administrator an early warning sign. It
will not prevent the machine from having problems when any key system
(/, /var, /tmp, swap) partition fills up.

For instance, if swap fills up (more likely if /tmp is on swap), then
the machine's performance will deteriorate dramatically, even if it
can still spawn processes.


If /var fills up you may not be able to su to root even if you are
logged into the box.  The computer may even crash.

It's fairly common to reduce the minfree on a partition if it's a
large user-oriented partition--the 10% default wastes a huge amount of
space when working with partitions over 100GB.


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