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[Patrick O'Callaghan]

On Fri, 2010-04-23 at 10:52 -0500, Chris Adams wrote:
> In old Unix, the sticky bit on an executable changed the way the
> kernel paged it into and out of RAM, but I don't believe Linux uses
> it.

Actually it meant the "text" segment (code and constant data) was
write-protected during execution, and hence could be shared between
multiple processes executing the same program. In fact that's why it was
called the "sticky" bit -- the text segment could stick in RAM even if
the process was swapped out, and in fact never needed to be swapped out
because it could always be reloaded from the executable file. This is
now assumed in the case of modern paging systems, but in the old PDP-11
it wasn't available on all models and could in some corner cases reduce
the total amount of virtual memory available to the process (you only
had a total of 8 physical segments of up to 32Kb each, and the stack
took up at least 1; later models allowed 16 segments total but 8 could
only be text and 8 could only be data or stack). Hence it had to be
user-modifiable.

Now I'm showing my age :-)

poc