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Documentation for Red Hat Enterprise Linux 3 (section 5.3.9.3) mentions these files in /proc/sys/kernel/:

  • sysrq
  • sysrq-key
  • sysrq-sticky
  • sysrq-timer

The documentation for RHEL 5 also mentions them.

Documentation for RHEL 6 does not mention any files except for sysrq.

If these files are mentioned in Ubuntu documentation, I can't find it. I also searched some of the Red Hat 5.x Release Notes, and I can't find it in there either.

The patch (against 2.4.11) to support these files (except sysrq-timer) was submitted to the kernel mailing list by Crutcher Dunnavant back in 2001; I don't know if it was ever officially accepted.

Checking current systems, I can't find the files (except for the sysrq file) on a RHEL 5.6 system nor on an Ubuntu Server Lucid Lynx 10.04.

What is the status of these files? Are they Red Hat-specific? Are they part of the kernel? Was the support removed? When?

Jeff Schaller
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Mei
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2 Answers2

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Here you go. It's in the kernel mainline, selectable by config.

Basically, sysrq enables/disables the physical magic, the others are for programmed control. The doc's pretty straightforward.

jthill
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I can only partially answer you questions.

No those files are not RH-specific: I found some hits in Google that are Debian related. Yes, they are part of the kernel, since SysRq is the fallback when everything else fails.

It is interesting that the RH5 documentation mentions it, while it seems to be gone in 5.6+

Nils
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  • Interesting. I only searched for Ubuntu and Red Hat; the patch is, of course, to the mainline kernel. I never did see any mention of `sysrq-timer` (nor was it in the patch) - though I wasn't really looking for it. Perhaps _that_ is RH-specific and not the others. – Mei Feb 03 '12 at 22:42
  • You are possibly right regarding `sysrq-timer`: all places where I found hints about it were related to RedHat 4 or Clones (CentOS, Oracle Unbreakable). So that part seems to be RH-specific and vanished somewhere between RH4 and RH5.6 – Nils Feb 04 '12 at 21:05