Re: visudo with Emacs

[Sven Joachim <svenjoac@gmx.de>]

On 2011-06-19 22:46 +0200, MON KEY wrote:

> On Sat, Jun 18, 2011 at 10:54 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>>> AFAICT the stray /etc/sudoers.tmp~ is not in keeping with the
>>> spirit of visudo. Emacs should operate equivalently with vi.
>>
>> ??? Why? what's wrong with leaving backup files in these use cases?
>
> AIUI visudo is an abstraction of an "atomic commit".
>
>  - When invoked visudo visits /etc/sudoers.tmp
>  - Edits are made.
>  - When the file is saved (read committed) it is verified for
>    correctness.
>  - If the the commit is successful, visudo writes to /etc/sudoers and
>    /etc/sudoers.tmp is removed.

More exactly, visudo renames /etc/sudoers.tmp to /etc/sudoers so that
the commit is indeed atomic.

> My impression is that neither /etc/sudoers.tmp nor the backup file
> /etc/sudoers.tmp~ are meant to be retained.

Since it serves as a lockfile, /etc/sudoers.tmp must not be retained
(visudo either renames or unlinks it, depending on whether you have made
changes or not), but /etc/sudoers.tmp~ does no harm.

>> If nothing else, you get for free the ability to easily restore the
>> original files, if you happen to screw up.
>
> Restoring from /etc/sudoers.tmp~ would amount to restoring from the
> lock file not /etc/sudoers !

And?  /etc/sudoers.tmp~ is still a backup file of /etc/sudoers and so
might be useful.

Cheers,
       Sven