GNU bug report logs - #74653
tail --follow=name doesn't exit when using inotify and the file is moved

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Message #13 received at 74653-done <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: Göran Uddeborg <goeran <at> uddeborg.se>,
 74653-done <at> debbugs.gnu.org
Subject: Re: bug#74653: tail --follow=name doesn't exit when using inotify and
 the file is moved
Date: Thu, 5 Dec 2024 12:55:29 +0000

[Message part 1 (text/plain, inline)]

On 04/12/2024 11:55, Pádraig Brady wrote:
> On 02/12/2024 16:19, Göran Uddeborg wrote:
>> When using "tail --follow=name", but without "--retry", on a file
>> supporting inotify, the command doesn't finish if the file is moved to
>> a new name.
>>
>> Repeat this way on a local filesystem:
>>
>>       echo apa > apa
>>       tail --follow=name apa &
>>       mv apa bepa
>>
>> "tail" will print an error message saying "No such file or directory",
>> but it will continue running. I would expect a following message "no
>> files remaining" and "tail" to exit.
>>
>> If the file system doesn't support inotify, if "apa" is on NFS for
>> example, "tail" exits as expected.
>>
>> If the file is removed rather than moved ("rm apa") "tail" also exits
>> as expected.
>>
>> This is tested on Fedora 41 using
>>
>> coreutils-9.5-11.fc41.x86_64
>> kernel-6.11.6-300.fc41.x86_64
> 
> Yes that is a bug.
> The info docs state this:
> 
> "In that [renamed file] case, use ‘--follow=name’ to track the named file,
>    perhaps by reopening it periodically to see if it has been removed
>    and recreated by some other program.  Note that the inotify-based
>    implementation handles this case without the need for any periodic reopening."
> 
> But that description only alludes to the implementation,
> and not any functional difference I would say.
> I.e. inotify should not imply --retry.
> 
> Interestingly if you `rm depa` before recreating "apa" in the example above,
> then tail does exit.  Also tail will exit immediately if "apa" is not present
> at startup.  Also tail will exit if you move "apa" to a different directory.
> All of those existing behaviors gives us latitude to adjust this behavior I think,
> so that tail does in fact exit for the case above with inotify.
> 
> BTW one can test the non-inotify behavior on any file system
> with the undocumented ---disable-inotify option.

I'll push the attached later to fix this.

Marking this as done.

thanks,
Pádraig

[tail-unfollow-renames.patch (text/x-patch, attachment)]

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