Re: mlocate/updatedb and btrfs subvolume mounts

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On Mon, May 04, 2015 at 04:40:08PM -0700, G. Richard Bellamy wrote:
> On Sun, Apr 12, 2015 at 9:12 PM, Duncan <1i5t5.duncan@xxxxxxx> wrote:
> >
> > Zygo Blaxell posted on Sun, 12 Apr 2015 16:11:07 -0400 as excerpted:
> >
> > > Since these are simple binds (not rbinds), they don't see any other
> > > filesystems, period.  They do see btrfs subvolumes, though.
> >
> > Tho... for systemd users...
> >
> > Do note that systemd plays with the kernel's shared-subtree "private"
> > default, switching it to shared for /.
> 
> I like to think I know a bit about a thing or two. I've read both Zygo
> and Duncan's probably cogent responses.
> 
> My brain hurts, and I am just not getting it.
> 
> If I am to understand correctly, and specific to my OP, the problem
> with updatedb et al. on my system is that /, /home, /var, /opt and
> /var/lib/libvirt are all subvolume mounts - which appear as bind
> mounts. Thus the PRUNE_BIND_MOUNTS prunes ALL mounts, and updatedb
> sees nothing.
> 
> Everything else is a blur when we start talking about "mount --bind /
> /.binds/root"
> 
> Oh wait, maybe I get it now...
> 
> By running "mount --bind / /.binds/root" and running updatedb in
> "/.binds/root" while still allowing it to see binds, I am certain to
> get a an mlocate db, and it won't ever see anything outside that
> explicit hierarchy.
> 
> Something like that?

Something like that.  You might also have to do 
'chroot /.binds/root <your-updatedb-script-here>' in order to get path
names that make sense from / (i.e. to prevent updatedb from adding
'/.binds/root' to everything).

Bind mounts are awesome.  And also evil.  ;)

> -rb
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