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Bug 1046818

Summary: A tail command gives an unnecessary message 'tail: inotify cannot be used, reverting to polling' even in non-follow mode
Product: Red Hat Enterprise Linux 6 Reporter: Masaharu Kawada <mkawada>
Component: coreutilsAssignee: Ondrej Vasik <ovasik>
Status: CLOSED ERRATA QA Contact: Tomas Dolezal <todoleza>
Severity: medium Docs Contact:
Priority: medium    
Version: 6.5CC: deleriux1, ooprala, pbrady, psklenar, tgl
Target Milestone: rc   
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: coreutils-8.4-33.el6 Doc Type: Bug Fix
Doc Text:
Cause: Previous update fixed the tail utility failure of the follow mode when dealing with symlinks incorrectly. Consequence: As result, tail utility was producing unnecessary warning about reverting to polling method (although inotify was not in use) Fix: Logic around the warning message was improved. Result: Warning informative message about switch to polling is no longer shown when not necessary.
Story Points: ---
Clone Of: Environment:
Last Closed: 2014-10-14 06:34:15 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description Masaharu Kawada 2013-12-27 01:15:07 UTC
Description of problem:

A tail command shows an unnecessary message 'tail: inotify cannot be used, reverting to polling' whenever it opens a symlink file. There is a similar issue in using tail command with '-f' option, however, with using the latest coreutils package shipped for RHEL6, it doesn't matter whether it's with '-f' option or not, the same happens always.

Version-Release number of selected component (if applicable):

coreutils-8.4-31.el6

How reproducible:

Always

Steps to Reproduce:
1.# touch testfile
2.# ln -s testfile testfile.symlink
3.# tail testfile.symlink

Actual results:

A tail command shows the message as follows.

ex)

# tail testfile.symlink 
tail: inotify cannot be used, reverting to polling

Expected results:

A tail command should NOT show the message 'tail: inotify cannot be used, reverting to polling'.

Additional info:

The below KCS seems to be related somehow.

Why running "tail -f" command print message "tail: inotify cannot be used, reverting to polling" while opening symlink?
https://access.redhat.com/site/solutions/634593

Comment 1 Ondrej Vasik 2013-12-27 08:15:26 UTC
For -F / follow-mode it is intentional behaviour - see https://bugzilla.redhat.com/show_bug.cgi?id=1006221 - and user should be notified about using polling instead of inotify. For non-follow mode, this is unintentional and the message is really unnecessary - thanks for the report.

Comment 2 Ondrej Vasik 2013-12-27 08:19:55 UTC
(as workaround, you could either make a wrapper around tail, which will filter out this error message for non-follow mode or you can use ---disable-inotify option as a default one (using polling instead of inotify) in the scripts which are fragile in the case of such error messages.

Comment 8 Ondrej Vasik 2014-05-15 09:07:39 UTC
*** Bug 1097802 has been marked as a duplicate of this bug. ***

Comment 10 Tom Lane 2014-08-24 15:34:09 UTC
If bug#1006221 were publicly readable, perhaps I could glean an explanation of why such a warning message is desirable.  But for the moment I'm with the complainant here: with or without -f, this message is a dumb idea.  It's strictly an internal implementation detail of tail, no?  Do you expect users to cancel their tail commands and do it some other way (and if so, what?)

Comment 11 Ondrej Vasik 2014-08-31 07:07:53 UTC
Without -f this message was just an accident. In documentation, -f says it uses inotify - to prevent periodical checks on followed files. This is probably why upstream decided to notify users about the change. You are right that most of the users don't care about this internal implementation detail. They will get the -f even with the polling mode. Adding upstream maintainer to CC, maybe he has better explanation why this message is displayed by default - maybe it is something for verbose mode.

Comment 12 errata-xmlrpc 2014-10-14 06:34:15 UTC
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHBA-2014-1457.html