Date: Tue, 12 Nov 2002 21:30:59 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: "Daniel O'Connor" <doconnor@gsoft.com.au> Cc: Hans Zaunere <zaunere@yahoo.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: Shared files within a jail Message-ID: <200211130530.gAD5UxNt067928@apollo.backplane.com> References: <20021113034726.75787.qmail@web12801.mail.yahoo.com> <1037159767.66058.34.camel@chowder.localdomain>
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Try using null mounts. The warning is in there because making the
null mount code work is a real hack and the authors aren't entirely
sure that everything's gotten covered. That said, use of a null mount
is certainly a lot safer if the stuff behind the mount is mostly
static.
Note that you can also use localhost NFS mounts to replicate pieces of
filesystems within jails, but you need to remember that the kernel
will wind up caching multiple copies of the data for these two cases
and that NFS has file locking issues.
Finally, keep in mind that disk space these days is quite cheap.
Duplicating the data is not as bad a way to go as you might think, and
it allows you to incrementally upgrade each jail. It may suffice to use
the null mount trick *only* for the big binaries and libraries that you
really want to share, and it may be reasonable to use softlinks to
accomplish it, like this:
JAIL FILESYSTEM:
/ complete copy of /
/usr complete copy of /usr
/mnt null mount of the master /
/mnt/usr null mount of the master /usr
And then use softlinks to enforce binary sharing by default:
/bin/* instead of the binaries make softlinks to /mnt/bin
/usr/bin/* ... softlinks to /mnt/usr/bin
/usr/lib/* ... softlinks to /mnt/usr/lib
/usr/local/lib/* ... softlinks to /mnt/usr/local/lib
/usr/local/bin/* ... softlinks to /mnt/usr/local/bin
So that way the user can remove the softlink and install his own
copy of the software if he wishes, and mess with anything else as well.
That's just an example. There are a thousand ways to do it.
-Matt
Matthew Dillon
<dillon@backplane.com>
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