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From: guy@gorodish.Sun.COM (Guy Harris)
Newsgroups: comp.unix.wizards,comp.arch
Subject: Re: R/O root (was: Jerry Pournelle on UNIX)
Message-ID: <39244@sun.uucp>
Date: 19 Jan 88 03:56:46 GMT
References: <1495@osiris.UUCP> <2126@haddock.ISC.COM> <1497@osiris.UUCP> <5247@elroy.Jpl.Nasa.Gov>
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> Having just recently learned of Sun's reorganizing of its disk layout
> for filesystems in SunOS 4.0, they do allow you to mount both / and
> /usr as read-only filesystems.  The root has been striped of all
> "dynamic" or machine dependant files. Most of /etc went to either
> /usr/etc or a seperate directory tree for machine specific stuff.  By
> doing this the root is only 1 megabyte and may be mounted read-only.

WRONG.  "/usr" may have been stripped of all dynamic stuff; however, much of it
got moved *to* the root file system.  All of the *programs* in "/etc" went to
"/usr/etc"; all of the configuration files stayed in "/etc", and some moved
from "/usr/lib" to "/etc" (e.g., "sendmail.cf".)  Directories such as
"/usr/spool", "/usr/adm", etc.  that might want to live on "/" if they don't
get too big or that might want to live on their own file system if they *do*
get big moved to "/var"; symbolic links have been left in the old places so
that references to "/usr/adm/messages", etc.  still work.

You could, perhaps, arrange to make "/" a read-only file system by making
"/etc" and "/var" both refer to some third read-write file system and by
changing "/etc/rc.boot" not to make "/" a read-write file system (the kernel
mounts it read-only, and only once it's passed "fsck" is it remounted
read-write), but I don't think we plan to guarantee this or support it.
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com