Re: Third /tmp location ? (and maybe a fourth too)

From: Zvezdan Petkovic (zvezdan@CS.WM.EDU)
Date: 02/26/02 

Date: Tue, 26 Feb 2002 15:56:49 -0500
From: Zvezdan Petkovic <zvezdan@CS.WM.EDU>
To: security@FreeBSD.ORG

On Tue, Feb 26, 2002 at 10:12:04AM -0800, Roger Marquis wrote:
> Bill Vermillion <bv@wjv.com> wrote:
> > > From: Dag-Erling Smorgrav <des@ofug.org>
> >
> > > Bill Vermillion <bv@wjv.com> writes:
> > > > > Is the /usr/tmp really used for somethink usefull ?
> > > > I would think man 7 hier will answer that for you in a hurry.
> > > > Yes it really is usefull.
> >
> > > Bzzzt. FreeBSD has never had /usr/tmp, and all software that expects
> > > /usr/tmp has been changed to use /var/tmp instead.
> >
> > And I set /usr/tmp for many things because there is no reason that
> > I can see to have var so big that it will hold large files I may
> > have to edit. I put /usr/tmp in almost all my .exrc files
> > as too many times I've gotten 'file system full'.
>
> File system full errors are typically caused by unnecessary
> partitioning. You rarely see them on single-partition systems.

But on a single-partition systems you can't make /usr read-only and File
System Hierarchy Standard is made exactly because of that. Multiple
partitions enable a clear distinctions between _shareable_ and
_unshareable_ data, as well as between _static_ and _variable_. Consider
this example (from FSH standard):

        +---------+--------------------+-----------------+
        | | shareable | unshareable |
        +---------+--------------------+-----------------+
        | static | /usr | /etc |
        | | /opt | /boot |
        +---------+--------------------+-----------------+
        | variable| /var/mail | /var/run |
        | | /var/spool/news | /var/lock |
        +---------+--------------------+-----------------+

In the above example if you use multiple partitions you can:

        * share /usr across the network
        * mount /usr read-only
        * mount /usr from read-only media such as CD-ROM
        * have to mount /var and / as read-write but if /var/mail is a
          separate partition you can share it across the network.
        * /etc, /boot, /var/run and /var/lock must be local to each
          machine.

There are obvious security advantages as well as flexibility in the
networked environment that cannot be achieved with a single-partition
systems. For the very simple environments though having a single
partition makes a lot of sense.

There are two schools of thought related to partitioning. Both are right
for there respective intentions. Notice that on a read-only /usr one
can't make /usr/tmp either. :-)

Best regards, 

-- 
Zvezdan Petkovic <zvezdan@cs.wm.edu>
http://www.cs.wm.edu/~zvezdan/
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