876535 – Document risks of using udevlog on kernel cmdline

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Bug 876535 - Document risks of using udevlog on kernel cmdline

Summary: Document risks of using udevlog on kernel cmdline

Keywords:
Status:	CLOSED ERRATA
Alias:	None
Product:	Red Hat Enterprise Linux 6
Classification:	Red Hat
Component:	udev
Sub Component:
Version:	6.4
Hardware:	Unspecified
OS:	Unspecified
Priority:	unspecified
Severity:	unspecified
Target Milestone:	rc
Target Release:	---
Assignee:	Harald Hoyer
QA Contact:	Leos Pol
Docs Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+	depends on / blocked

Reported:	2012-11-14 11:20 UTC by Marian Csontos
Modified:	2015-07-22 07:19 UTC (History)
CC List:	5 users (show)
Fixed In Version:
Doc Type:	Bug Fix
Doc Text:	If "udevlog" is specified on the kernel command line to debug udev, all udev logs are stored in the /dev/.udev/udev.log file. Running a system with the udev debug log turned on and using "udevlog" on the kernel command line for an extended period of time could cause /dev/.udev/udev.log to become very large and the devtmpfs mounted on /dev to become full. Consequently, if /dev became full, no new symbolic links and device nodes could be included. With this update, start_udev contains a verbose warning message describing the possibility.
Clone Of:
Environment:
Last Closed:	2015-07-22 07:19:28 UTC
Target Upstream Version:
Embargoed:

Attachments	(Terms of Use)

Links
System	ID	Private	Priority	Status	Summary	Last Updated
Red Hat Product Errata	RHBA-2015:1382	0	normal	SHIPPED_LIVE	udev bug fix update	2015-07-20 17:58:19 UTC

Description Marian Csontos 2012-11-14 11:20:19 UTC

Description of problem:

Running system with udevlog specified on kernel cmdline may cause problems once the udev's devfs is full - looks like udev rules are not executed: I have had lvremove and vgremove leaving behind symbolic links in /dev/$VGNAME and the directory itself, causing problems when recreating the VG.

The problem is not obvious:
- the tail of udev.log is not very helpful - it contains only old data.
- no full fs reported by df or memory reported by top (it's visible in free yes)
- no helpful message in /var/log/messages

One should be warned when enabling this feature and decrease log-priority after successful boot.

One should clean the file once over certain size, by ': > /dev/.udev/udev.log'.


Version-Release number of selected component (if applicable):
udev-147-2.42.el6.x86_64


How reproducible:
100%


Steps to Reproduce:
1. start system with udevlog on kernel cmdline
2. run vgcreate/lvcreate/lvremove/vgremove in a cycle - vgcreate will fail after some time due to existing /dev/VG.


Actual results:
Looks like udev rules are not executed when devfs is full - lvremove/vgremove leaving symlinks in /dev/VG


Expected results:
- documented risks
- errors in messages
- udev errors should be send also to syslog

Additional info:

Comment 2 Harald Hoyer 2012-11-28 14:52:09 UTC

How do you know about "udevlog" in the first place?

Comment 3 Marian Csontos 2012-11-28 15:15:07 UTC

(In reply to comment #2)
> How do you know about "udevlog" in the first place?

Source code is the best decumentation.

Is this one of the "undocumented" features one's not supposed to use?

Comment 4 Harald Hoyer 2012-11-28 15:26:31 UTC

(In reply to comment #3)
> (In reply to comment #2)
> > How do you know about "udevlog" in the first place?
> 
> Source code is the best decumentation.
> 
> Is this one of the "undocumented" features one's not supposed to use?

Yes, it's an "undocumented" debugging feature for customer debugging support. :-)

If you use it, you should be aware of the problems it causes. Of course, I can document it in the source code of the shell script.

Comment 5 RHEL Program Management 2012-12-14 08:33:07 UTC

This request was not resolved in time for the current release.
Red Hat invites you to ask your support representative to
propose this request, if still desired, for consideration in
the next release of Red Hat Enterprise Linux.

Comment 6 Wade Mealing 2013-09-17 04:37:29 UTC

Another alternative is to repeat the warning in the form of a kcs article.

Comment 8 Leos Pol 2015-04-15 09:11:17 UTC

# grep -A2 udevlog start_udev 
	if strstr "$cmdline" udevlog; then
                echo 'WARNING: udevlog is active!' >&2
                echo "$udev_root/.udev/udev.log can grow big very quick and resides in RAM" >&2
                echo 'Turn off udev logging as soon as you booted!' >&2

Comment 9 errata-xmlrpc 2015-07-22 07:19:28 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.

https://rhn.redhat.com/errata/RHBA-2015-1382.html

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