Date: 10 Mar 2003 16:10:04 -0600 From: Guy Helmer <ghelmer@palisadesys.com> To: Andrew J Caines <A.J.Caines@halplant.com> Cc: hackers@FreeBSD.ORG Subject: Re: mount_null evil ? Message-ID: <1047334204.23435.26.camel@volans.palisadesys.com> In-Reply-To: <20030310213213.GE87518@hal9000.halplant.com> References: <20030310132402.GA93784@LF.net> <20030310213213.GE87518@hal9000.halplant.com>
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On Mon, 2003-03-10 at 15:32, Andrew J Caines wrote: > Marc, > > > I?m currently developing a jail-management solution - I use a > > readonly mount_null for central software-management of the jails. > > The manpage was written May 1, 1995 - is using this tool still dangerous > > I have used it for read-only mounts since way back and have not have any > problems, including brief periods of high I/O. > > I'd have reservations allowing unique data on a read-write mount, however > I just did a few quick and simple tests of reads and writes on a rw null > mount on my 4.8-RC box with no apparent problem. I seemed to be able to crash the kernel regularly under FreeBSD 4.5 when I used null mounts to share a read-only filesystem between jails. My application frequently rebuilt the jails by unmounting everything, wiping out the old jail subdirectories, writing new jail subdirectories, and remounting the shared read-only fs into each jail subdirectory. I gave up on null mounts and went back to having a separate copy of the entire filesystem for each jail. If null mounts work better now, I'll revisit it... Guy -- Guy Helmer <ghelmer@palisadesys.com> To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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