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Date:      Tue, 18 Apr 2000 00:05:14 -0600
From:      Chris Fedde <cfedde@fedde.littleton.co.us>
To:        Salvo Bartolotta <bartequi@neomedia.it>
Cc:        freebsd-questions@FreeBSD.ORG
Subject:   Re: re-reading /etc/fstab ... 
Message-ID:  <200004180605.e3I65Eh22956@fedde.littleton.co.us>
In-Reply-To: <20000417.23514600@bartequi.ottodomain.org> 

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On Mon, 17 Apr 2000 23:51:46 GMT  Salvo Bartolotta wrote:
 +------------------
 | Dear FreeBSDers,
 | 
 | yet another question :-)
 | 
 | If I turn on e.g. the "noatime" option on a ufs filesystem (eg "/" or 
 | "/usr"), and I want to have my /etc/fstab re-read, I seem to 
 | understand that I have to reboot.
 | 
 | Alternatively, If I do NOT wish to reboot, I should issue a "shutdown" 
 | command (with no options whatsoever), unmount the filesystem(s), and 
 | remount them. 
 | 
 | The problems arise with the "/" filesystem. Incidentally, "mount -u /" 
 | might damage it. In particular, I seem to understand that switching 
 | from read only to read/write is harmless; whereas switching from 
 | read/write to read only may actually damage the FS -- especially if 
 | this happens a few times. 
 | 
 | Is there a safe way to turn the option on without rebooting in such 
 | cases ? Am I (yawn) missing anything trivial ?
 | 
 | Many, many thanks for your help (and patience !)
 | 
 | Best regards,
 | Salvo
 +------------------

Taking a file system from rw to ro while it is active can cause
some data to be lost. mount -u protects against causing a problem
unless you have the "force" option on.  Taking a fs from ro to rw
while it is active is not a problem.

You can mount and unmount non active file systems to your heart's content
and change their options using -u and mount will do its best to prevent a
problem.

I'd do the experimentation on the command line before committing
it in fstab.  It is safe to run 'mount -a -u'  as long as the changes
in /etc/fstab are benign. 

chris
--
    Chris Fedde
    303 773 9134


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