[Duplicity-talk] Restoring regular files with sticky bit

[Peter Schuller]

Hello,

so I encountered a situation where duplicity is unable to restore a
backed up file because the source file was a regular file with the
sticky bit set. On FreeBSD, a non-root user cannot set a sticky but on
a regular file. Presumably the sticky bit was originally set as a
result of the operation being performed by root (perhaps during an
rsync -avWP).

The question is how one would want duplicity to handle it. I
definitely think it should do something sensible, or allow for it,
since you do not want to have to sort this out on the spot.

A few possibilities:

* Introduce a --no-sticky-on-regular-files (or similar) switch which
  would disable attempts to set the sticky bit during restores.

* Automatically re-try a chmod without the sticky bit if a chmod ever
  fails with the sticky bit being requested.

* Never attempt to preserve the sticky bit.

I think I favor the first possibility because it would not affect
preservation by default while allowing users a way out when having
this problem. Perhaps try to give the user a hint that this may be the
problem when os.chmod fails.

I don't like disabling preservation alltogether since the sticky bit
might be there for a reason :) The re-try does not feel good either
because you can imagine situations where a file will be incorrectly
restored as a result of some transient error that made the chmod fail,
so the process becomes non-determinstic. Even without that problem, I
don't like "silent non-preservation".

Any opinions?

-- 
/ Peter Schuller

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