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    SubjectRe: About /etc/mtab and /proc/mounts
    Miles Bader wrote:
    >
    > Kasper Dupont <kasperd@daimi.au.dk> writes:
    > > > /var is clearly the right place for this;
    > >
    > > Is it?
    >
    > Yes. On some systems, /var and /tmp are the _only_ read-write filesystems.

    OK, but then on such a system with my approach it would be possible to
    make /mtab.d a symlink pointing to somewhere under /var.

    >
    > > > if /var isn't mounted initially, I'd suggest that mount should
    > > > simply not update any file at that point, and the init-script that
    > > > mounts /var can be responsible from propagating information from
    > > > /proc/mounts to /var/whatever.
    > >
    > > Would you fsck /var while it is mounted?
    >
    > No, of course not; that's why I suggest it's up to the init scripts to
    > make sure that /proc/mounts gets propagated to /var/whatever. They
    > usually will know enough about what's going on to take care of any
    > special cases and add any extra info that's relevant.

    But AFAIK fsck uses mtab.

    >
    > If a program such as `mount' wants to use mtab and finds that it's not
    > present (possibly because /var isn't mounted), it should either use
    > /proc/mounts instead, or just ignore it.

    If mtab does not exist mount will attempt to create a new one with
    only the root listed.

    >
    > > I think part of the problem is that /var is used for both files
    > > we want to keep across reboot, and files we do not want to keep
    > > across reboot.
    >
    > [/var/run is for `non-persistant' files]

    But that doesn't solve the problem with ordering. If we don't want
    to change a lot of userspace utilities and the order in which things
    are done during boot, we need /var/run mounted earlier than /var.
    And /var/run is not the only directory with files we do not want to
    keep across boot. There are some in /var/lock too, and AFAIR a few
    other locations.

    >
    > > There are cases where it is undesirable to have mtab in /var,
    > > but if mount expect to find mtab somewhere under /var, we can't
    > > even use a symlink to get it out of there, because /var needs
    > > to be mounted before the symlink can be followed.
    >
    > It will simply appear to mount as if the file isn't present, in which
    > case it should gracefully stop trying to use it [see above].
    >
    > It seems like the attempt here is to somehow make everything just work
    > magically _without_ modifying any tools that use mtab -- and I think
    > that just isn't doable in every situation.

    Maybe not, but I certainly don't want to change every program that
    reads mtab. If we can limit the changes to those tools that needs
    to write mtab, it might be feasible.

    --
    Kasper Dupont -- der bruger for meget tid på usenet.
    For sending spam use mailto:aaarep@daimi.au.dk
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