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

Ted Ts'o <tytso@mit.edu> writes:

> On Mon, Aug 16, 2010 at 09:01:42PM +0200, Bernhard R. Link wrote:
>> * Perry E. Metzger <perry@piermont.com> [100816 20:21]:
>> > The most reasonable argument against altering such things is that
>> > after decades, people are used to the whole /usr thing and the fight
>> > to change it isn't worthwhile. That I will agree with -- see the
>> > emotional reactions people get when you suggest their preferred layout
>> > is an "onion".
>> Accusion people of irrational behaviour almost always results in
>> irrational behviour. Either they were irrational already before or
>> making false insulting accusations. So I should better not tell you
>> that accusing people of irrational behaviour is quite irrational...
> There is a rational reason for doing this at least for servers.
> Having a small root partition can be a huge advantage because it
> minimizes the chances that it will get corrupted.  Making the root
> read-only is even better from that perspective (but generally requires
> more work).  What I like to do for servers that absolutely, positively
> can't go down, and for which I don't have redudant servers (mainly
> because I'm too poor :-) is to have a root partition which is small
> (say, half a gig) and then mirror it onto another partition on a
> separate spindle, and set up grub so I can boot off of either root
> partition.  (If the BIOS has a way for me to specify via a serial
> console booting off of the 2nd hard drive, even better; then I can
> have a duplicate grub setup on the 2nd hard drive as well.)
> I used to do this for desktops as well, but these days, a rescue CD is
> easy enough to use.
> 						- Ted

It's been a while since I converted a fresh install to read-only / +
/usr. Do you know what is left that does need work? Bugs should be filed
for any remaining problems since a read-only / and /usr should work
practically out of the box.

Here are some other reasons:

1) The root filesystem is checked with the filesystem mounted and any
alteration of the filesystem can conflict with the kernels caches so it
is a bit of a risky thing. For that reason if any alterations are done
the system reboots. Reboot take time and you might have to yet again
walk down into the cellar and input the passphrase for decrypting /.

2) The check is also done verry early and I think swap isn't mounted at
that point. With a small / the chance of corruption is less and the fsck
will be over faster and use less ram.

3) On a small FS seek times will be smaller and fragmentation happens
less. So it is faster. (More a reason why /var should be seperate.)

4) If you do have filesystem corruption (not on / but say /usr) then the
root filesystem has enough tools to fix things.


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