Red Hat Bugzilla – Bug 104912
RFE: would like echo p > /proc/sysrq-trigger to show registers
Last modified: 2007-11-30 17:06:53 EST
From Bugzilla Helper: User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0) Description of problem: Is it possible to get echo p > /proc/sysrq-trigger to show registers. I opened a call with RedHat support on this and they told me to submit a RFE (Request for Enhancement) on bugzilla. Basicall, echo m > /proc/sysrq-trigger works as well as echo t > /proc/sysrq-trigger. However, echo p > /proc/sysrq-trigger does not work. Many times when I call redhat support, they ask for the output of this syrq "p" trigger. It would be handy if you could do this remotely or from a script instead of having to be sitting in front of the console and hitting the <alt> <sysrq> keys. Version-Release number of selected component (if applicable): 2.4.9-e.27smp How reproducible: Always Steps to Reproduce: 1. echo 1 > /proc/sys/kernel/sysrq 2. echo p > /proc/sysrq-trigger 3. Actual Results: dmesg and /var/log/messages show this line: SysRq: Show Regs That's it nothing else is printed. If you go to console and hit <alt> <sysrq> <p> than registers get dumped. Expected Results: Expect registers to get dumped. Additional info: Tested this on e.24, e.27 and beta Linux Enterprise 3 kernel.
If "echo p > /proc/sysrq-trigger" dumps the registers, you are almost certain to see a process in the middle of sys_write(2), to a file in /proc. More precisely, it'll be writing to /proc/sysrq-trigger. I'm not sure how dumping that info would be very useful, since you know what's happening on your cpu when you echo something to /proc/sysrq-trigger ... However, let me know if I've overlooked something (I wouldn't be surprised).
You bring up a good point, if the only info you'll gather is capturing a syswrite from the "echo p" process, than I guess that doesn't make a whole lot of sense. Is there any way to dump the regs remotely if you're not in front of the console?
Over serial console you can trigger sysrq commands. By default you need to send a break, followed by the sysrq letter. In /proc/sys/kernel/sysrq-key you can configure another special key, which is useful if your terminal program doesn't want to send a break.
Closing as this appears to be resolved.