Interesting - I noticed this in /usr/include/bits/fcntl.h the other day (as one does), and wondered whether any of them might be useful:

#ifdef __USE_GNU
# define F_SETLEASE 1024    /* Set a lease.  */
# define F_GETLEASE 1025    /* Enquire what lease is active.  */
# define F_NOTIFY   1026    /* Request notfications on a directory.  *
+/
#endif
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Prompted by your suggestion, I found that these are actually documented in more recent versions of the fcntl(2) manpage than I have, such as in this HTML version.

Unfortunately it notifies only of processes opening or truncating a file, and you have to be the owner of the file (or root), which means it isn't very useful for my current needs.

I see also that there is a fam rpm for my O/S - but while I wasn't able to Google any docs on how to use it, I did find a number of threads about how insecure it was (due to its dependency on portmapper), which makes me reluctant to try it.

Hugo