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.
Questions tagged [magic-sysrq]
46 questions
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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
X11 and svgalib, to XLATE mode
What is raw mode?…
Lesmana
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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 work in my still running X server.
Now whenever I…
Bjarke Freund-Hansen
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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 SysRq key to discover if it's working.
Quora Feans
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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 key has an additional label like "SysRq".
Update…
Al Klimov
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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 checked if SysRq was enabled...
> sysctl…
Caesar Kabalan
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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+SysRq and enter them without releasing…
Ruslan
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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 serial consoles?
anarcat
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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't even have a login prompt), but nothing.
Things…
MightyPork
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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, B giving sufficient time between each of these keys to…
BufBills
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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.
Documentation for RHEL 6 does not mention any files…
Mei
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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 3.9.5):
SysRq : Show Memory
Mem-Info:
DMA…
kirelagin
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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/syslog.
Please assume that I do not have root…
c0rp
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If /etc/sysctl.conf doesn't exist, where is my sysctl storing configs?
I want to change two values using sysctl. One is the sysctl vm.swappiness=10 and the other, sysctl kernel.sysrq=1. However, when I run sysctl -p, it tells me sysctl: cannot open "/etc/sysctl.conf": No such file or directory, but sysctl -a returns…
Akshat Vats
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How can I map a specific keyboard key to be SysRq?
I am using Parabola GNU/Linux (Arch variant) on a MacBook Pro laptop. I would like to configure/enable the SysRq key, since I am experiencing fairly frequent system freezes, which are forcing me currently to have to hard-reboot the system. I have…
Time4Tea
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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 file as /etc/sysctl.d/95-sysrq.conf where I…
user306023