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

Josh Boyer jwboyer at fedoraproject.org
Wed Feb 25 15:12:12 UTC 2015

On Wed, Feb 25, 2015 at 9:53 AM, Michal Schmidt <mschmidt at redhat.com> wrote:
> 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?

Rescue mode quite often translates to "debug mode" as well.  Things
hang, you need to know why, etc.  SysRq isn't always required, but it
is another tool in the box.


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