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Re: why are there /bin and /usr/bin...

On Sun, 15 Aug 2010 16:00:23 -0700 Steve Langasek <vorlon@debian.org>
> On Sun, Aug 15, 2010 at 06:30:04PM -0400, Perry E. Metzger wrote:
> > By the early 1990s this was long since unneeded but people
> > continued to do it anyway, and in fact started to think it was
> > done for technical reasons rather than because of a simple lack
> > of space in an earlier era. At this point (2010), with all of the
> > system files fitting in under a dollar's worth of disk space,
> > people tell themselves quite elaborate "just so" stories about
> > why the segregation is maintained.
> You wrongly assume here that every Unix system has a hard drive as
> its root filesystem.  Some root devices cost a lot more than a
> dollar for that amount of disk.

Ah, onions.

In the embedded space, which I know a lot about, it is true that the
root FS is on flash or other expensive media -- but it isn't like /usr
is on cheaper media in such an environment, it is always part of the
root fs anyway, so it makes no difference. (If you're talking about,
say, someone with an SSD just for the boot drive, I assure you that
were awk or basename or what have you on /bin it would not make any
observable difference in their cost. Indeed, a typical set of binaries
on even a workstation laden with all the latest gadgets won't make any
real difference here.)

> Some have breakpoints beyond which it becomes an order of magnitude
> more expensive to expand the root device.

Yes, yes, but as I noted, it is almost never the case that /usr is any
differently priced, so it makes no difference. The notable difference
are people who use SSDs as their root device, and even there, it turns
out that in practice such people are putting everything but /home and
such on the SSD, and the difference in cost between 1G of SSD and 10G
is minimal.

This whole thing goes back to casual decisions made in the 1970s when
there weren't even a dozen unix machines in the world and even a 5M
hard drive was an astonishingly expensive piece of equipment, but
people are still attached to it. I suspect that in 2050, people will
still be making the same argument.

I have no actual expectation that anyone is going to change how this
is done, because /usr is so heavily ingrained in people's experience
of Unix even though it is an onion.

Perry E. Metzger		perry@piermont.com

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