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Questions tagged [magic-sysrq]

The "magic sysrq" key sequence is a feature of the Linux kernel that, when enabled, provides debugging and disaster recovery features on the system console and serial console.

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Undo Magic SysRq “remount-ro”

Is there a way to undo an accidental Magic SysRq "remount-ro"? On my notebook keyboard, this combination happens all too often... I tried to remount the roor partition with mount -o remount,rw /dev/...
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How to ensure SysRq is always enabled regardless of the kernel.sysrq setting?

Some Linux distributions have kernel.sysrq=16 which means only Sysrq+s (sync) is allowed. As an example: Fedora (25 and 28) has it set as such in /usr/lib/sysctl.d/50-default.conf I had to create a ...
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reisub, get detailed processes usage

I'm using the magic SysRq keys when my computer is frozen. The downside is that with REISUB, there is no detailed feedback of the computer state: I would like to find which processes are causing the ...
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Why does SaK kill gdm, which is running on a different VT?

I run Fedora Linux 28, and have enabled sysrq. I pressed Alt+PrtScr+K, to kill a non-responsive X session. But this also restarted gdm, and one other X session, which were running on different VTs. ...
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Can't figure out the way to trigger Magic Sys Keys via keyboard debian 9 lxdm 0.53-2 xfce4.12.3

I use a debian 9 with Magic Sys Keys enabled : sysctl -a | grep sysrq kernel.sysrq = 1 if I trigger in CLI, it works : echo f > /proc/sysrq-trigger I have something like : emergency sync ...
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Set kernel.sysrq = 1 in /etc/sysctl.d/10-magic-sysrq.conf using command? [duplicate]

I wish to use a single command line instead of opening the text editor to change the parameter of the file /etc/sysctl.d/10-magic-sysrq.conf to kernel-sysrq = 1 from any current parameter, even if ...
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Under what circumstance could switching tty's and entering commands freeze?

I noticed, that when booted from a live disc, and the RAM is filled up nearly, the live DVD starts being accessed far more often (probably due to exhausted and squished block cache) and switching tty'...
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SysRq output into |less, |more, |tee?

If I issue a SysRq command, how do I redirect that output (whether it is stdout or stderr is documented nowhere) to |less, |more or |tee?
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How to stop a SysRq command?

I used SysRq+J (thaw), now I am being flooded with printk messages: emergency thaw on sr0. It will never stop. I do not wish to wait, until a SysRq command ends while blocking the terminal all the ...
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Reasons for CTRL+PrtScr+R+E+I+S+U+B

If Linux stops responding one might be forced to make an unclean shutdown and in this case one might unknowingly just turn off the power. I read that you should try and make a soft reset with ctrl+...
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Cannot get kernel crash dump saved and reboot

I need to get a crash dump of my linux kernel. I am going to describe the scenario: Hardware: Notebook Dell E5450. Linux Distribution: Linux Mint 18.3 (Ubuntu 16.04). SysRq: enabled by /etc/sysctl.d/...
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Can a magic sysreq key combo run a script?

I'm experiencing system hangs which seem to correlate with high RAM usage levels (though swap is mostly unused). I'd like to be able to kill thunderbird and other memory hogs via a script with a ...
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does “echo -m > /proc/sysrq-trigger” run in process context when it runs from script?

we have a script which runs below sysrq command to get memory info in syslog and then script copies the syslog. echo -m > /proc/sysrq-trigger From documentation I see that at the at kernel level "...
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Why is Magic SysRq not enabled by default on some systems? Is there a risk?

While troubleshooting a Oracle Linux 6.3 server (RHEL Derivative) I tried to use some of the Magic SysRq Key commands for the first time. No such luck so I had to hard reboot. When it came back up I ...
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How to send SysRq command over ssh connection?

I am working on BeagleboneBlack based custom board, Recently I was debugging system hang issues, I had access to debug console using minicom, And I could enable log using key combination Ctrl+A, F `. ...
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Kernel Crash/ Cpu error?

First I will describe my system and then my problem: I have an Assus F555L laptop with an i3 and Intel Integrated Graphics. It is running Linux Mint 17.3 and Windows 10 dual booted. I do not have ...
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What is the difference between 'reset' and 'ctrl sysrq b' (for Linux 2.6.x)

What is the difference between the two? In a Linux 2.6.x kernel.
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How to make SysRq working on laptop?

My /proc/sys/kernel/sysrq contains the number 502, but Alt+SysRq+... seems not to work on my HP Pavilion laptop. How can I fix that? Update 1: By the way: neither my print-screen-key nor any other ...
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How to discover whether magic SysRq key is enabled, and what keys invoke it?

How can I know what keys will invoke the magic SysRq key? Provided I am in front of a Linux machine which is not frozen (yet). I need something easier than trying all common combinations of magic ...
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What are the programs/commands which the magic SysRq key invoke?

From Magic SysRq key The magic SysRq key is a key combination understood by the Linux kernel, which allows the user to perform various low level commands regardless of the system's state. It is ...
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How to read the output of the show-memory-usage SysRq?

I couldn’t find any (recent) documentation on reading the output of the show-memory-usage SysRq (Alt+SysRq+m). So what can one learn from looking at it? Here is an example output form my box (Kernel ...
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Alt+SysRq+T not working / Where do SysRq commands print to?

My REISUB commands, and K, work flawlesly, but with T (it should print info about tasks), it prints nothing. H also doesn't work. Alt+SysRQ+H Alt+SysRQ+T I tried in all tty's (even F10, which doesn'...
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Why does Alt+SysRq+B not always trigger while REISU do?

On many different machines, when I come across a lockup, I often use Alt+SysRq+REISUB to reboot without too much losses. But I often noticed that although REISU commands work even when I just hold Alt+...
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In Linux, why do you need to be root to write to /proc/sysrq-trigger?

WARNING: THE NEXT KEY COMBINATION WILL CRASH YOUR COMPUTER Ok, I get that this is an administrative tool and all, but I realized that any user can do ALT + SysRq + C. This link explains what I'm ...
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Remote executing Magic Sys Rq

Is it possible to execute Magic SysRq keys on remote machine, using SSH? For example I'm trying to run like this: xdotool key Alt+Sys_Req+H But I do not see any help in console, neither in /var/log/...
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How long should I wait between keystrokes when doing SysRq + REISUB?

I read this from here: The most useful combination is the Alt+SysRq/Prnt Scrn + R-E-I-S-U-B. The above basically means that while you press and hold Alt+SysRq/Prnt Scrn and press R, E, I, S, U,...
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What numeric key codes do I need to send for the magic sysrq functionality in a VNC session?

I have access to the system console of a KVM guest through VNC. What key codes do I need to send for the magic sysrq sequence (Ctrl+Alt+"REISUB") in Linux? Edit: In Linux under qemu, running showkey ...
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how to reboot a frozen FreeBSD server from the serial console?

Linux has the "magic sysrq key" to reboot frozen machines remotely, and it works over the serial console, but what about FreeBSD? Is there a way to send a "control-alt-delete" to FreeBSD servers on ...
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sysrq won't reboot with a keystroke, but will with echo “b” > /proc/sysrq-trigger

CentOS 6.2, 2.6.32-220.el6.x86_64 laptop. SysRQ is enabled for keyboard input, as is witnessed by: $ cat /proc/sys/kernel/sysrq 1 Common Magic SysRQ Keys are working such as alt-sysrq-h. However, ...
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Linux /proc/sys/kernel: where are the files sysrq-sticky, sysrq-key, and sysrq-timer?

Documentation for Red Hat Enterprise Linux 3 (section 5.3.9.3) mentions these files in /proc/sys/kernel/: sysrq sysrq-key sysrq-sticky sysrq-timer The documentation for RHEL 5 also mentions them. ...
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Sysrq keeps taking screen shots

I have enabled SysRq in the kernel like this: $su #echo 1 > /proc/sys/kernel/sysrq and confirmed that it worked. Fn-F1 is my SysRq key, but every time I press Alt-Fn-F1 and any other letter ...
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REISUB (Alt+SysRq+key) doesn't work on Slackware13.37_64, KDE

Under Slackware I never used the magical REISUB, and never used KDE (I don't know if it is important). But now I installed a Slackware13.37_64 with KDE, and, as far as I know, I didn't modify anything ...
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Recovering from Sys Rq + r

I had a really bad lockup of my X server and had to do a Sys Rq + r to release my keyboard from X and get into a console. I was able to kill the process that was locking up my system, and continue my ...
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What is raw keyboard mode?

In the magic sysrq key combinations, there is the combination alt+sysrq+r which, according to wikipedia, does the following: Switch the keyboard from raw mode, the mode used by programs such as ...