Read-only disk problem

Engineering ee at
Mon Aug 29 20:28:26 UTC 2011

Hello all.


Please let me know if this is the wrong place to ask. I am working on an
embedded system using FreeBSD 7.2, bootinf and running off of flash memory.
In order to not burn out the flash, I use the 'diskless' scripts and mount
the flash read-only. I have used this configuration successfully in the


I've recently added a utility to check for disk corruption, basically
checksumming the / and /usr partitions. Since they are both read-only, I
thought this would work. What I have discovered is that something in the
partition is changing between boots.


I dd'd the flash over a couple of boots, and compared the binaries to see
what was changing. It is a small amount of data, spread across the disk, in
an interval that looks very similar to the interval of the 'superblocks'


Is there any data that is written to the disk at boot or mount time, and if
so, is there a way to prevent it?




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