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From: Joe Greco <jgreco@brasil.moneng.mei.com>
Message-Id: <9501131657.AA02484@brasil.moneng.mei.com>
Subject: Re: About readonly root partition
To: martin@innovus.com (Martin Renters)
Date: Fri, 13 Jan 1995 10:57:27 -0600 (CST)
Cc: luigi@labinfo.iet.unipi.it, hackers@FreeBSD.org
In-Reply-To: <199501131534.HAA11820@freefall.cdrom.com> from "Martin Renters" at Jan 13, 95 10:38:02 am
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> > 	So, How about letting "init" look for "/rc" instead/before
> > looking for /etc/rc ? This would help in having the following:
> > 
> > 	1) a main "rc" is called, which does the initial checks;
> > 	2) mounts the proper filesystem onto /etc;
> > 	3) passes control to /etc/rc
> > 
> > With the current setting, the above might still work except that, once
> > the new /etc is mounted, the original /etc/rc is no more readable.
> 
> /etc, /tmp, and /var all need to be separate for each diskless client.
> 
> I do agree that it would be a good idea to do something to allow selective
> mounting at system startup time. Perhaps init could tell that it is running
> diskless and run some sort of shared '/etc/diskless.rc' script which could
> mount the correct /etc, /tmp and /var filesystems based on some system
> administrator defined scheme.
> 
> An example /etc/diskless.rc might contain:
> 
> 	mount server:/exports/etc/$hostname /etc
> 	mount server:/exports/tmp/$hostname /tmp
> 	mount server:/exports/var/$hostname /var
> 
> And then execute /etc/rc (which would now be the system specific one)

Perhaps define a search path for "rc" in init?  "/sbin/rc:/etc/rc" and by
default do not provide an /sbin/rc.  If one exists, in this case, it could
be something like

mount server:/exports/etc/$hostname /etc
. /etc/rc

I hacked around this by making my root NFS partition writable (bypassing all
these problems).   I have always hacked around similar problems in the past,
as well.  Typically I mount / rw, and /usr ro, which means that I have to
have a per-system /, but I have a little script that hardlinks share-able
files rather than copying them, so that in essence /etc, /var, and /tmp are
unique on each box, but /bin's binaries are shared.  My little wonder-script
to do this is appended at the end.  Tailored for our local environment, 
alas.  It's cheesy, it's quick, it's dirty.  No apologies.  :-)  brasil is
my SunOS 4.1.3 workstation with lotsa disk.  I'm always shopping for a
better solution, though...

People are arguing things about DISKLESS being undesirable and the
like, but in reality I find that it is very effective to be able to
walk up to an arbitrary PC here at work, cram a disk in, and be running
UNIX and X a few minutes later.  Very impressive demonstration of a
technically superior operating system.  ;-)  

... Joe

-------------------------------------------------------------------------------
Joe Greco - The Data Capture Fellow (and UNIX/Network Hacker)      414/362-3617
Marquette Electronics, Inc. - Milwaukee, WI        jgreco@brasil.moneng.mei.com

% cat /nfs/2.0S/root/dup
#! /bin/sh -
master=master
dup=$1

mkdir ${dup}
(cd $master; find * -print) | (
	while read i; do
		if [ -h ${master}/$i ]; then
			echo symlink `ls -l ${master}/$i | awk '{print $10}'` ${dup}/$i
			ln -s `ls -l ${master}/$i | awk '{print $10}'` ${dup}/$i
			continue;
		fi
		if [ -f ${master}/$i ]; then
			case "$i" in
				etc/*|var/*)
					echo copy ${master}/$i ${dup}/$i
					cp -p ${master}/$i ${dup}/$i;;
				*)
					echo link ${master}/$i ${dup}/$i
					ln ${master}/$i ${dup}/$i
			esac
			continue;
		fi
		if [ -d ${master}/$i ]; then
			echo mkdir ${dup}/$i
			mkdir ${dup}/$i
			chown -f `ls -ldg ${master}/$i | awk '{print $3 "." $4}'` ${dup}/$i
			continue;
		fi
		if [ -c ${master}/$i ]; then
			continue;
		fi
		if [ -b ${master}/$i ]; then
			continue;
		fi
		if [ -p ${master}/$i ]; then
			continue;
		fi
	done
)
chmod 1777 ${dup}/tmp ${dup}/var/tmp
echo ${dup} > ${dup}/etc/myname
chmod 644 ${dup}/etc/myname
echo ${dup} > ${dup}/etc/hostname.ed0
chmod 644 ${dup}/etc/hostname.ed0
echo "151.186.20.4	brasil" >> ${dup}/etc/hosts
echo "151.186.20.x	${dup}" >> ${dup}/etc/hosts
vi + ${dup}/etc/hosts
(
echo "brasil:/nfs/2.0S/root/${dup}	/		nfs rw 0 0"
echo "brasil:/nfs/2.0S/usr		/usr 		nfs ro 0 0"
echo "brasil:/nfs/2.0S/usrsrc		/usr/src	nfs ro 0 0"
echo "brasil:/nfs/2.0S/local		/usr/local	nfs ro 0 0"
echo "brasil:/nfs/2.0S/X11R6		/usr/X11R6	nfs ro 0 0"
) > ${dup}/etc/fstab
chmod 644 ${dup}/etc/fstab