Why sysrq is limited to only "sync" command on official fedora kernel?

Michal Schmidt mschmidt at redhat.com
Wed Feb 25 14:53:41 UTC 2015

On 02/25/2015 03:43 PM, Josh Boyer wrote:
> On Wed, Feb 25, 2015 at 9:35 AM, Ali AlipourR <alipoor90 at gmail.com> wrote:
>>>> Why sysrq is limited to only "sync" command on official fedora kernel?
>>> The kernel itself isn't limited.  It's just set that way in
>>> /usr/lib/sysctl.d/50-default.conf which is provided by systemd.  You
>>> can edit that file, create your own in /etc/sysctrl.d/, or (as root)
>>> set it to whatever you would like via /proc/sys/kernel/sysrq.
>> Of course it can be changed at runtime, but I mean why official fedora
>> kernel shouldn't be configured to allow all (or at least a wider
>> subset) of sysrq commands by default?
> Maybe we're getting hung up on a terminology issue, but this isn't a
> kernel configuration issue.  It's something userspace is doing.
>> This way official fedora live CDs are unsuitable for system recovery
>> tasks; you have to change sysrq value every time you use live CDs or
>> build your own live CD.
> That's a good point.  Since the live images have a "rescue" mode,
> maybe there is a way to use a different value when booted into that.
> How that would look, I'm not sure.  Maybe dracut would need to include
> an override file in the initramfs.

I don't follow the reasoning. Why am I more likely to need SysRq in
rescue mode than in normal boot?


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