Change the executing of a 0-byte file to be an error...

Garance A Drosihn drosih at
Fri Jun 10 05:33:07 GMT 2005

A few months ago, I had a system panic happen right in the middle of
a 'installworld'.  Right now I don't care about the panic itself
(IIRC, it was a hardware problem), but there was one unexpected
side-effect which caused me more trouble than the original panic.
And all that trouble boils down to the following:

    If a file is empty and executable, that empty file can be
    executed without generating any error.

The panic caused a few files in /usr/bin to end up as zero-byte
executable files, but I didn't realize that.  I ended up doing
another buildworld, I think it was, and ended up digging myself
into a deeper and deeper hole.  The problem included things like
makefile rules calling:

      somecmd | sort -blah | domore

where the 'sort' command had turned into one of those zero-byte
executable files.  The basic result was that the more I tried to
rebuild parts of the world, the more screwed up the system became.
By the time I was done, I had to do a clean install from CD-ROM
to get it back to working order.

Can anyone think of a real-world problem that would come up if the
system was changed so that executing a 0-byte file would cause an
error?  I read through a few likely pages in SUSv3, and it looked
like the behavior for executing an 0-byte file is not explicitly
defined.  Of course, it might be that I was simply looking in the
wrong part of the standard.

It does seem like empty files are also executed without error on a
few other OS's I tried, but I don't understand why that behavior
would be desirable.

Garance Alistair Drosehn            =   gad at
Senior Systems Programmer           or  gad at
Rensselaer Polytechnic Institute    or  drosih at

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