Messages in this thread | | | Date | Thu, 27 Feb 2003 01:21:21 -0800 | From | jw schultz <> | Subject | Re: About /etc/mtab and /proc/mounts |
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On Thu, Feb 27, 2003 at 05:42:30PM +0900, Miles Bader wrote: > Kasper Dupont <kasperd@daimi.au.dk> writes: > > > 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. > > ... you could do the same with /etc/mtab. > > In fact since /etc is almost guaranteed to be on the same filesystem as > /, it seems like "/mtab.d" offers zero advantages over just /etc/mtab -- > the case where /etc/mtab is the most annoying is when /etc is R/O, but > this almost always means that / will be R/O, making /mtab.d useless too.
If you netboot /etc as its own filesystem make sense. Why duplicate the rest of root just for /etc. /etc, /var and /tmp are the only filesystems that have much reason to be unique to a system; all others are easily sharable and most others read-only.
> > > But AFAIK fsck uses mtab. > > It uses /etc/fstab. > > > If mtab does not exist mount will attempt to create a new one with > > only the root listed. > > Unless you use the `-n' flag, which an init-script should do if it > knows there's something wierd required to get /var mounted or something.
<voice of annoyance> /etc/mtab is a hack. I suspect it was done so that fsck, df and umount wouldn't have to read /dev/kmem. We now have much better ways to get data out of the kernel.
The idea of storing the list of mounted filesystems on a mounted filesystem is a bad idea from the get-go. The only advantage it ever really had was the possibility to manually play mountpoint monte with mv. Duplicating the in-kernel data externally begs for inconsistencies that only get worse with pivot root.
Let the data reside in the kernel and have a procfs or sysfs entity for it. A symlink from /etc/mtab can keep the old tools happy.
-- ________________________________________________________________ J.W. Schultz Pegasystems Technologies email address: jw@pegasys.ws
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