Bug 1473207

Summary:	sysctl does not display vm.stat_refresh parameter even if the /proc/sys/vm/stat_refresh file exists
Product:	[Fedora] Fedora	Reporter:	Matus Marhefka <mmarhefk>
Component:	procps-ng	Assignee:	Jaromír Cápík <jaromir.capik>
Status:	CLOSED NOTABUG	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	medium	Docs Contact:
Priority:	medium
Version:	26	CC:	jaromir.capik, jcerny, jrybar, rzilka
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Last Closed:	2017-08-14 15:22:27 UTC	Type:	Bug
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Description Matus Marhefka 2017-07-20 08:38:51 UTC

Description of problem:
When listing all kernel parameters using sysctl, the vm.stat_refresh parameter is not displayed. This is a bug as the /proc/sys/vm/stat_refresh file exists on the filesystem.


Version-Release number of selected component (if applicable):
procps-ng-3.3.10-11.fc24.x86_64
procps-ng-3.3.10-13.fc26.x86_64


How reproducible:
always

Steps to Reproduce:
$ ls -l /proc/sys/vm/stat_refresh
-rw-------. 1 root root 0 Jul 19 15:54 /proc/sys/vm/stat_refresh
$ sysctl -aN 2>/dev/null | grep stat_refresh


Actual results:
`sysctl -aN` output does not list vm.stat_refresh parameter when the /proc/sys/vm/stat_refresh file exists.


Expected results:
`sysctl -aN` output lists vm.stat_refresh parameter when the /proc/sys/vm/stat_refresh file exists.

Comment 1 Roman Žilka 2017-07-20 16:35:37 UTC

Same behavior here. The omission of this particular parameter in the output of sysctl seems to be happening at sysctl.c:282 (ReadSetting(), vanilla procps-ng-3.3.12). Each parameter whose /proc file is empty doesn't get its name printed. And the said file (/proc/sys/vm/stat_refresh) is indeed empty on my system. It is actually the only empty (readable) file under /proc/sys.

I don't know if this is a bug or a feature in sysctl, but from the looks of the code it could be intentional behavior.

Comment 2 Jan Rybar 2017-08-14 15:22:27 UTC

From the documentation in kernel source:
"
stat_refresh

Any read or write (by root only) flushes all the per-cpu vm statistics
into their global totals, for more accurate reports when testing
e.g. cat /proc/sys/vm/stat_refresh /proc/meminfo
"

It seems that this parameter is intentionally blank and for very special purposes we do not want sysctl to trigger. Hence I find it correct not to list this parameter since it is not directly tunable.