How System Requests Work and How to Add Your Own SysReq

I needed to add a custom System Request (Sys Req or SysRq) to a linux kernel some time ago. While doing so, I dug deep into how it works and I thought I’d make a quick post about it. Here is a good SuperUser answer about what a SysRq is. You may also know about SysRq via REISUB. This post has three parts: how to raise a SysRq, how SysRq works (looking into kernel code), and how to add your own SysRq.

Disclaimer: This is my website.


Amazing. I’ve been ‘staring’ at the sys rq key for 20 years with Linux and many years before with Win/Dos, and never really knew how it worked, for what, or if it was still used for anything - even then.

Apparently (from light search) sysreq was mostly used in the old days to halt current job and enter a systems menu.

Anyway, thanks for fixing a long-standing knowledge gap :-)


I’m glad you appreciate it! It’s always fun digging into kernel internals and learning new things :D


No one knows what SysRq was meant for.

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