[ILUG] repair permissions

[Brian Foster]

  | From: Niall O Broin <niall at linux.ie>
  | Date: Fri, 18 Mar 2005 00:13:17 +0000
  | 
  | On 17 Mar 2005, at 20:03, Brian Foster wrote:
  | > my answer is the classic paper by Rob Pike and Brian W Kernighan,
  | > “Cat -V Considered Harmful”, http://netlib.bell-labs.com/cm/cs/doc/
  | 
  | Of similar quality to most of these gentlmen's published writings,
  | I don't think it's particularly relevant here.

 then we disagree.  the problem, as I see it, is an un-necessary
 functionality (and option) was added to chown(1), chmod(1), and
 chgrp(1) — recursively descending a directory hierarchy — and it
 does not even work!  try (as a normal user, not the superuser):

    mkdir A
    touch A/F
    chmod -R 0 A

 with GNU `chmod', the following happens:
   • the mode of A/ is changed to the requested 000 (Ok).
   • the error “chmod: `A': Permission denied” is issued (bad).
   • the mode of A/F is not changed (bad).

 that example may be slightly artifical, but alter the mode
 to be 400 (or 440 or 444) instead of 0, and you have a very
 plausible scenario:  the user clearly wants all the _files_
 to be readonly.  a trivial task using find(1).  but impossible
 with `chmod -R':  the mode is not only applied to files _and_
 directories (mistake 1) but also top-down (mistake 2).†

 so what is the fix?  add yet more of `find's capabilities
 into `chmod'?  (in this case, probably `-depth' and `-type'.)
 this sort of thing is just what Pike et.al. were complaining
 about — a poorly thought-out case of featuritis begating yet
 more problems, “features”, and a thicker manual.  yet without
 improving the overall generality/power of the system in any
 obvious manner.

  | > in case it is not clear, I maintain `chmod -R' is a badly designed
  | > tool, arguably produced by “haphazard hacking”, and `find' is the
  | > power tool.
  | 
  | It was clear enough. I happen to disagree. Would you also remove the -r
  | option from rm & chown ?  [ ... ]

 NO.  now, today, some c.20(!) years after the deed, I would
 not remove `-R' from the 3 `ch...'s (nor `r' from `rm', but
 that is a different case anyways).‡    but I might consider
 deprecating `-R'?

 *speculating* (I was not at UCB at the time and do not know
 the rationale for the decision — which is why, in my first
 post, I asked why BSD added `-R'), I would have _not_added_
 `-R' to `chmod', `chown', and `chgrp' in the first place.

 ( nor `-v' to cat(1), or the columniation to ls(1)  ;-)
  esp. as the system I was using at that time had the
  general-purpose tools mc(1) and vis(1) Pike et.al.
  mentioned in the paper. )

 incidently, how does `cat -v' play with UTF-8?  ;-)

cheers!
	-blf-

 †  you only need to change the directory mode after
   the mode of all contained files and (recursively)
   subdirectories have been changed, which perhaps is
   not strictly “bottom-up”, but close enough...

 ‡  it would not be a good idea to remove `-r' from `rm' for
   completely different reasons.  here is a hint as to why:
   `rm' changes the contents of directories.  combine with
   `find' and ....   oops!:  could be made to work, but a
   hierarchy-altering operation does not play well with a
   concurrent hierarchy-scanning operation.
-- 
Experienced (20+ yrs) kernel/software Eng: | Brian Foster   Montpellier,
 • Unix, embedded, &tc;  • Linux;  • doc;  | blf at utvinternet.ie   FRANCE
 • IDL, automated testing, process, &tc.   |  Stop E$$o (ExxonMobile)!
Résumé (CV) http://www.blf.utvinternet.ie  |     http://www.stopesso.com