Re: Gnumeric file went south.

[Morten Welinder <terra diku dk>]

This is quite complicated to get right.

Emacs takes care of...

* Missing write permission in the directory.  (Backup goes to home directory
  with a message.)

* Hard-linked files.

* Writable files owned by other users and/or groups.

Some Emacs docs to ponder...

Morten



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backup-by-copying-when-mismatch's value is t

Documentation:
*Non-nil means create backups by copying if this preserves owner or group.
Renaming may still be used (subject to control of other variables)
when it would not result in changing the owner or group of the file;
that is, for files which are owned by you and whose group matches
the default for a new file created there by you.
This variable is relevant only if `backup-by-copying' is nil.
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backup-by-copying-when-linked's value is t

Documentation:
*Non-nil means use copying to create backups for files with multiple names.
This causes the alternate names to refer to the latest version as edited.
This variable is relevant only if `backup-by-copying' is nil.
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backup-by-copying's value is nil

Documentation:
*Non-nil means always use copying to create backup files.
See documentation of variable `make-backup-files'.
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make-backup-files's value is t

Documentation:
*Non-nil means make a backup of a file the first time it is saved.
This can be done by renaming the file or by copying.

Renaming means that Emacs renames the existing file so that it is a
backup file, then writes the buffer into a new file.  Any other names
that the old file had will now refer to the backup file.  The new file
is owned by you and its group is defaulted.

Copying means that Emacs copies the existing file into the backup
file, then writes the buffer on top of the existing file.  Any other
names that the old file had will now refer to the new (edited) file.
The file's owner and group are unchanged.

The choice of renaming or copying is controlled by the variables
`backup-by-copying', `backup-by-copying-when-linked' and
`backup-by-copying-when-mismatch'.  See also `backup-inhibited'.
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