GNU bug report logs - #6960
mv refuses to move a symlink over a hard link to the same file

Previous Next

Full log

View this message in rfc822 format

From: Jim Meyering <jim <at> meyering.net>
To: Eric Blake <eblake <at> redhat.com>
Cc: 6960 <at> debbugs.gnu.org, Anders Kaseorg <andersk <at> MIT.EDU>
Subject: bug#6960: mv refuses to move a symlink over a hard link to the same file
Date: Wed, 04 Jan 2012 22:00:55 +0100

Eric Blake wrote:

> On 01/04/2012 01:32 PM, Anders Kaseorg wrote:
>> This refusal makes it impossible to overwrite a hard link with a symlink
>> _atomically_.
>
> It is already impossible to overwrite a directory with a symlink
> atomically; then again, the only time rename() allows overwriting a
> directory is if it is empty, and removing an empty directory before
> putting a symlink in its place is not a form of data loss.  But whether
> the inability to atomically overwrite a directory with a symlink should
> carry over to a refusal to atomically overwrite a regular file with a
> symlink is a different matter.
>
>>> Personally, I prefer the semantics of 'mv -f --backup=numbered' so use a
>>> shell alias.
>>
>> mv --backup=numbered is not atomic; it expands to two rename() syscalls,
>> between which the target doesn’t exist at all.
>
> Maybe we should fix that, to make mv --backup use link()/rename() rather
> than rename()/rename(), so that there is no window where the target
> doesn't exist.

Note that we can use link/rename only some of the time.
E.g., the rename will always fail when they're on different partitions.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.