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Re: Default size limits for /run (/var/run) and /run/lock (/var/lock)



On Sat, Apr 16, 2011 at 09:35:53AM +0200, Goswin von Brederlow wrote:
> Roger Leigh <rleigh@codelibre.net> writes:
> 
> > On Fri, Apr 15, 2011 at 04:41:56PM +0200, Goswin von Brederlow wrote:
> >> Roger Leigh <rleigh@codelibre.net> writes:
> >> 
> >> > If it wasn't already clear, having /tmp as a tmpfs is a
> >> > /configurable option/, and it is /not/ the default (except when
> >> > root is read-only (ro) in fstab).
> >> 
> >> I hope you check the fstab first. If there is a entry for a non tmpfs
> >> /tmp filesystem then that should be used. I'm assuming you do but just
> >> to be sure...
> >
> > No, we don't check.  It's up to the admin to configure their
> > system properly.  If there is an entry in in fstab, it'll be
> > mounted on top of the tmpfs, so the system will be configured
> > the way they asked, but there will be a hidden tmpfs mount.
> > But they would have explicitly needed to set RAMTMP=yes to get
> > into this situation.
> >
> > For new installs, where the default /etc/default/rcS files does
> > set RAMTMP=yes by default, the fstab file will not yet contain
> > any user-specific mounts.  If they do want to manuall mount
> > something on /tmp, then they simply set RAMTMP=no.
> >
> > Note this behaviour is exactly the same as existing practice for
> > /dev/shm, /var/run and /var/lock.
> 
> Then I don't get your 'is /not/ the default (except when root is
> read-only (ro) in fstab)'.
> 
> To me that reads like you will mount a tmpfs on /tmp if root is
> read-only even if RAMTMP is not set. Which is wrong if the system has a
> /tmp filesystem in /etc/fstab.

This is a good point.  I've added the ability to detect if a
filesystem will be mounted, and skip the tmpfs mount on /tmp if
an entry for /tmp exists in fstab (will_mount in
/lib/init/mount-functions.sh)

> Also mount -a (in mountall.sh) fails, and therefore the whole boot, if a
> mountpoint already has something else mounted. If you unconditionally
> mount a tmpfs on /tmp if root is read-only then you just made systems
> unbootable that have /tmp in fstab.

This is not correct.  Have you actually tried it?  I have, and other
than the cosmetic issue of having a real filesystem mounted over the
top of the tmpfs, the system is entirely functional, and boots error
free.  And with the above change, even this cosmetic issue is gone.


Regards,
Roger

-- 
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