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Re: Why mount -o remount,ro /usr (sometimes) fails after apt-get dist-upgrade?



hiya,

On Mon, Nov 11, 2002 at 11:56:02AM +0200, Shaul Karl wrote:
>   Basically, when one removes a binary file from a UNIX file system, it 
> is gone - no matter if this binary is currently in use. Therefore, 

i don't think that's necessarily true.  i believe the way it works is
that a file is not 'gone' (in the sense of fs de-allocation) until there
are no more references to it.  so for example, i think if you open a
file for reading, and then immediately remove the file, you should still
be able to read the entire file, even if it's over a page in size.
you could verify this with a simple c-program or perl script where you
open the file, then rm it via system(), and then read the data.

now i could be wrong (and feel free to correct me if i am), but i think
executing the file also counts as a reference to it in some way, so when
you delete the file and/or overwrite it with an upgrade, if the program
is running in memory it should be just fine and should be able to load in
pages that weren't already in memory, but as soon as it exits the file
is 'gone'.  in the meantime that the program is running, subsequent
calls to exec/read that file will get the new file (or fail if it was
simply removed).  

--sean

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