For some reason, my Linux machine will properly turn off when striking SysRq+O, but won't reboot as expected when doing SysRq+B.

我在天马彩票平台输了三十万Both of these ones show up in the help message (with SysRq+H) and all my SysRq options are enabled:

$ cat /proc/sys/kernel/sysrq 

I use a 11-years-old machine (Intel Q9550 / ASUS P5E3, assembled by myself) that currently runs a Fedora 31 linux distribution, but the problems shows up at least since Fedora 25我在天马彩票平台输了三十万. I first suspected the custom kernels from this distribution to be the cause, but it seems to occur with self-compiled genuine kernels too.

It also used to work in the past and with other distribs such as Knoppix, but I can't remember when it started to happen.

Nothing happens nor shows up when I do SysRq+B, neither on console nor dmesg log. Every other option (in particular, R, E, I or S) seems to be OK, and to produce log trafic. Does anybody know what could cause the reboot operation to be disabled ?

This leads my to a "secondary" question:

Inside the kernel source, at rows 447 and 469 of drivers/tty/sysrq.c我在天马彩票平台输了三十万, I can see:

        &sysrq_reboot_op,               /* b */


        /* o: This will often be registered as 'Off' at init time */
        NULL,                           /* o */

So rebooting (which not currently works for me) is supposed to be always defined by default while turning off (which does work) is set to NULL, then defined at init time. I couldn't find which is this actor, nor at what exact time this powering off option is enabled. Could you help me on this too ?

Many thanks in advance for your help.

EDIT : lastest kernel at write time is 5.5.1 but the code quoted above belongs to 5.4.15 and older, and I'm running the Redhat's 5.4.15-200.fc31.x86_64 package.


Finally, it turns out to be due to the same problem than in this related entry. It worked by releasing Syst while maintaining Alt, then pressing B.

This surprises me a little bit because I use a desktop machine using a PS/2 keyboard port (not an embedded laptop keyboard). I used to work with a cheap Logitech keyboard that has always been a pain, but seemed to do the job anyway. When this keyboard died, I installed back an old Compaq keyboard from years 2K (Model KB-9963) that works pretty well and is much pleasant to use, but visibly suffers from the same problem.

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