CentOS - Jun 2015 - newbie question on installation over existing Linux

On Jun 8, 2015, at 8:16 PM, g <geleem at bellsouth.net>
wrote:
> 
> On 06/08/2015 09:11 PM, John R Pierce wrote:
>> On 6/8/2015 6:29 PM, Peter wrote:
>>> You can thank Fedora for making that rather pointless change and 
>>> breaking that capability.
>> 
>> that 'capability' was a holdover of the 1980s when disks were
>> measured in megabytes, and memory in kilobytes, so large file
>> systems were impractical.
> 
> gee, you sure about that?
Yes.

And this is not a case of Fedora picking fights with the rest of the Linux
world.  /usr was already assumed to be on the root FS in Solaris, FreeBSD, OS X,
and Cygwin well before Fedora made their decision.

Fedora?s late to the party, and CentOS necessarily even later.
> was tha 8 bit or 17 bit?
Unix has never seriously been deployed on 8-bit systems.

Even oddballs like Xenix on 8088 and uCLinux on H8/300 are only ?8 bit? because
of the external address bus.  These are just gimped 16-bit processors, not true
8-bitters.

Unix started out on a PDP-7, an 18-bit machine, before moving to a PDP-11/20,
which was 16-bit, but much more powerful than the -7.  The reduction in word
size is a reflection of the rise of ASCII and power-of-2 data size standards,
not indicating any real reduction in power.

I don?t know about *any* 17-bit processors.

Warren Young wrote:
> /usr was already assumed to be on the root FS in Solaris, FreeBSD
I'm using both Solaris and FreeBSD quite extensively and, honestly,
have never heard of that assumption. In fact, on the machine that I'm 
currently typing this message on, the file systems look like this:

    # uname -sr; mount -t ufs
    FreeBSD 10.1-RELEASE
    /dev/da0s1a on / (ufs, local, journaled soft-updates)
    /dev/da0s1d on /tmp (ufs, local, journaled soft-updates)
    /dev/da0s1e on /var (ufs, local, journaled soft-updates)
    /dev/da0s1f on /usr (ufs, local, journaled soft-updates)

(Everything else, especially /home, is NFS-mounted.)

Patrick

On Jun 10, 2015, at 12:49 PM, Patrick Hess <patrickhess at gmx.net>
wrote:
> 
> Warren Young wrote:
>> /usr was already assumed to be on the root FS in Solaris, FreeBSD
> 
> I'm using both Solaris and FreeBSD quite extensively and, honestly,
> have never heard of that assumption.
I don?t have a ?real? Solaris installation here to try, but the OpenIndiana,
DilOS and SmartOS forks of OpenSolaris all symlink /bin to /usr/bin.  I expect
the same is true of Solaris 11, though I wouldn?t be surprised to learn that
Solaris 10 still kept /usr separate, given its 2005 release date.

As for FreeBSD, I?m basing that on the fact that the last time I tried moving
/usr to a ZFS volume, back in the days when it could only boot to UFS, the
system couldn?t even boot into single user mode.  I had to reinstall the OS to
fix that box.

I suspect if I tried UFS-root + ZFS-/usr again today, on a 10.1 box, it would
succeed as a side effect of the root-on-ZFS support, but only because it would
allow /usr to come up early enough to allow the boot to proceed.  I suspect if
you nuked /usr, it again would fail to boot.

The bottom line is that we now live in a world where even the piggiest OSes will
install with room to spare on a throwaway removable flash drive.  The rationale
behind /usr-free single-user boots is defunct.