Question

1

Setup shortcut keys not working

rated 0 times [ 1] [ 0] / answers: 1 / hits: 1891 / 3 Years ago, thu, november 18, 2021, 2:43:18

In my Ubuntu 12.04, in keyboard settings, I didn't find a shortcut for restarting X, so in "Custom Shortcut", I set up Ctrl + Alt + Backspace for the command sudo restart lightdm. But the shortcut doesn't work. Is it because it requires root privilege?

Also I have a SysRq key on my keyboard, which I think is the "Magic SysReq Key". My SysRq key is shared with PrtSc key (for screen shot), and is in blue which means I have to press Fn key at the same time to invoke SysRq instead of PrtSC.

But every time I press Fn + SysRq, it always produces a screenshot, just as when I hit PrtSc without hitting Fn. I wonder how to use the Magic SysReq Key? Does it mean the shortcut has not been linked to any command that is defined for Magic SysReq Key yet?

PS: My laptop is Lenovo T400 and OS is Ubuntu 12.04.

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answered 3 Years ago tigehanc · Accepted Answer

Answer for the 1st question.

In order to restart your X server with "Ctrl + alt + Backspace",

Open "System Setting > Keyboard Layout".

On Keyboard Layout, click the option button in bottom right corner.

Expand “Key Squence to kill the X server” and then check "Ctrl + alt + Backspace"

enter image description here

Answer for the 2nd question.

Magic SysRq keys active by default in Ubuntu 12.04 LTS.

You can check to execute this command:

sudo cat /proc/sys/kernel/sysrq

Then, you can see "1" in terminal, this means "enable all functions of sysrq".

To perform a safe reboot, use REISUB SysRq Magic combination key:

Hold Alt + Fn + SysRq then type R+E+I+S+U+B , you need to press each key for 2-3 seconds.

Caution: Don't release Alt + Fn + SysRq, when you type R+E+I+S+U+B. And, after you type "E", black screen comes out. But you have to continue typing "I+S+U+B".

So, you can reboot your PC safely.

Safely shutting down Ubuntu when it is frozen, use "R+S+E+I+U+O" keys instead of "R+E+I+S+U+B".

Meaning of each keys:

B: Will immediately reboot the system without syncing or unmounting your disks.

O: Will shut your system off (if configured and supported).

R: Will switch the keyboard from raw mode, the mode used by programs.

S: Will attempt to sync all mounted filesystems.

U: Will attempt to remount all mounted filesystems read-only.

P: Will dump the current registers and flags to your console.

T: Will dump a list of current tasks and their information to your console.

M: Will dump current memory info to your console.

E: Send a SIGTERM to all processes, except for init.

I: Send a SIGKILL to all processes, except for init.

L: Shows a stack backtrace for all active CPUs.

I think that you may arrange the combination of these keys (after considering the meaning of the keys) , since this is an example.

You can reboot system using only B command key, or shutdown using only O command key. But, especially , it may be important to remount a file system safely by "read-only" using U key, to protect that a file breaks in the case of forced termination.