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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 
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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.

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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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