Does Your PC Really Need a SysRq Button Anymore?

An anonymous reader writes "Ever wondered what the SysRq key on your keyboard does? Lenovo has decided it's so rarely used that it has started removing the key from some new Thinkpad Edge laptops. We already know that Lenovo are something of the fastidious scientists when it comes to keyboard design. Last time they fiddled with the age-old key layout, it was after painstaking research to count exactly how many times users press the Delete and Escape keys. Now it seems another relic of computer keyboards is starting to disappear."

Comments

Linux, Specifically Ubuntu

[Aldenissin]

I use the "busier" backwards or "reisub" combination with the sysrq key in order to gently shutdown Ubuntu when it locks up. So yes, I use it, but that has only been in the last couple of years or so. Not sure what else it is used for...

I've used it

[jonbryce]

If linux freezes, then Alt-SysRq-S+U+B will do an emergency sync of the disks, unmount them and reboot the system.

Re:I've used it

[luder]

I actually use Alt - SysRq - R + E + I + S + U + B:

        * R: Switch the keyboard from raw mode to XLATE mode
        * E: Send the SIGTERM signal to all processes except init
        * I: Send the SIGKILL signal to all processes except init
        * S: Sync all mounted filesystems
        * U: Remount all mounted filesystems in read-only mode
        * B: Immediately reboot the system, without unmounting partitions or syncing

You don't need to hold the REISUB keys, so you can use your left hand to hold Alt, your right one to hold SysRq and use the free fingers to type REISUB.

Re:I've used it

[ais523]

You don't. You hold down alt and sysrq, but the other keys are pressed in sequence (and rather slowly). (Some laptop keyboards with sysrq requiring fn require you to let go of sysrq while you press the other keys, in which case you hold down alt but alternate between sysrq and the other characters.)

Incidentally, for the grandparent: you probably want to write the whole sequence of 6 commands, R E I S U B, rather than just S U B. The R sets the keyboard to raw mode, sometimes allowing you to control-alt-f1 into a terminal and fix the crash without rebooting. E tells all the processes which are still running properly to terminate (many of them will save crash recovery or autosave data if you do that, so you can more easily get back to where you were); I kills all the processes that didn't shut down when you pressed E. This means that when you use S to synchronise the disks, it actually saves what you want to save, and nothing tries to queue up more data to save afterwards. Then U remounts filesystems readonly (or unmounts them; it comes to much the same thing), and B reboots the system instantly (the REISU do the rest of the shutdown process between them).

A good mnemonic for this is that REISUB is "busier" spelt backwards. (Raising Elephants Is So Utterly Boring is another common mnemonic.)

Sometimes I end up doing REISUO instead; unlike REISUB which is a manual reboot, RESIUO is a manual shutdown. It all rather depends on whether you want the system to stay down or come back up.

Re:Debug key

[ais523]

This conflicts badly with Ubuntu's decision to make Alt-Sysrq+K the default way to kill X (as opposed to control-alt-backspace which is too easy to press by mistake), too.

Re:I don't recall ever using it...

[OnlineAlias]

SysRq is the print screen button, and I use it all of the time too. It is cut and paste for me, alt-printscreen (or control-printscreen) then shift-printscreen. Fastest screen paste in the west....

Comment removed

[account_deleted]

Comment removed based on user account deletion

Re:Goodbye to the ThinkPad brand.

[Chalex]

The laptops that are getting this change are the Thinkpad Edge models. They are the low-end consumer level Lenovo laptops, Thinkpads in name only. They are not the regular Thinkpad T or X or R series models. The R series is discontinued now anyway. The regular T and X series are staying as they were (with minor modifications). You can read more details here: http://lenovoblogs.com/insidethebox/?p=349

I look forward to the Thinkpad T series being the solid black square tanks that they have always been.

Re:Debug key

[thebasicsteve]

Ubuntu didn't change the key. On any kernel with the "magic SysRq key" enabled (which Ubuntu has), Alt+SysRq+K kills all running processes on the current VT. Therefore, it kills X.
Ubuntu's recent decision to disable Ctrl+Alt+Backspace by default is a separate issue.
On older versions of Ubuntu, you will find that either key combo will kill X.

Re:Debug key

[colin_s_guthrie]

I think you're confused. Alt+SysRq+K is one of the Linux "Magic Keys" http://en.wikipedia.org/wiki/Magic_SysRq_key it kills all processes on the current VT, not just X. Most modern X implementations will still work with Ctrl+Alt+BkSp but you now need to do it twice and the first time it makes a rather ominous "beeeeeeeeeep" at you to warn you that you maybe about to make a bad decision....

So this is hardly an "Ubuntu decision" (like most distros they just package up what's already there, mix it up with a few good and a few bad ideas of their own and paint it nicely).