this post was submitted on 07 Feb 2024
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Why is SYSRQ Disabled on most consumer distributions? (lemmy.ml)
submitted 9 months ago by Artemis_Mystique@lemmy.ml to c/linux@lemmy.ml
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I use fedora on a 11ish year old laptop(It had decent specs for its time).

recently i encountered an issue while playing a 11 hour webm video(celluloid flatpak) i had downloaded off youtube,

the screen froze, I could still hear the video sound playing, but the system wasn't responding to any keyboard presses(Wouldnt switch over to TTY2-4),

I had heard about REISUB and tried it, but it obviously didnt work, after about 2:30 mins the system unfroze and i was shuffled Across numerous TTY's and the video closed as i had invoked CLTRL+Q

I am not here for a resolution to my problem The issue is reproducible by loading numerous instances of videos whose combined watch time Exceeds about 7-8 hours

I am more curious as to why SYSRQ is disabled and are there any consequences in enabling it(Security Wise)?

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[–] Atemu@lemmy.ml 27 points 9 months ago (1 children)

There are some obvious security risks involved in fully enabling the SysRq key. In addition to forcing reboots and the like, it can be used to dump the contents of the CPU registers, which could theoretically reveal sensitive information. Since using it requires physical access to the system (unless you go out of your way), most desktop users will probably consider the level of risk acceptable. That said, make sure you fully understand the implications of enabling it and the dynamics of the larger context in which your system is operating before you turn SysRq all the way on.

https://wiki.archlinux.org/title/Keyboard_shortcuts#Enabling

I don't care about this so sysrq is enabled on all of my desktop systems.

[–] Artemis_Mystique@lemmy.ml 11 points 9 months ago* (last edited 9 months ago) (3 children)

That said, make sure you fully understand the implications of enabling it

Are there any other risks to worry about except abuse due to physical access?

The wording makes it feel kinda Ominous, can improper use potentially lead to a borked system?

[–] Atemu@lemmy.ml 15 points 9 months ago (1 children)

Improper use of sysrq can absolutely lead to a borked system or other breakages as it allows you to initiate unclean shutdowns or kill all processes which can have consequences.

If your system is stuck though, sysrq is often your only option short of hardware shutdown.

[–] drwho@beehaw.org 4 points 9 months ago (1 children)

Especially if you're prone to accidentally hitting SysReq instead of PrintSc by accident.

[–] Artemis_Mystique@lemmy.ml 2 points 9 months ago

but on my keyboard they are the same key? Hitting ALT+PRTSC took an instant screenshot

[–] 0v0@sopuli.xyz 12 points 9 months ago

Yes, for example, syncing on a kernel panic could lead to data corruption (which is why we don't do that). For the same reason REISUB is not recommended anymore: The default advice for a locked-up system should be SysRq B.

[–] avidamoeba@lemmy.ca 1 points 9 months ago* (last edited 9 months ago) (2 children)

What do you mean by "most consumer distributions"? It's enabled on Ubuntu. At least REISUB is.

[–] SteveTech@programming.dev 1 points 9 months ago (1 children)

Last I checked, only SUB (Sync, Unmount, reBoot) is enabled by default, you have to edit a sysctl config for REI (Raw keyboard, SIGTERM, SIGKILL) to do anything.

[–] avidamoeba@lemmy.ca 1 points 9 months ago* (last edited 9 months ago)

Hm. Actually I wouldn't have noticed if REI didn't work when the computer appeared frozen. Just SUB part would have done enough. So you might be right.

[–] Artemis_Mystique@lemmy.ml 1 points 9 months ago

I didn't know that, It wasn't working on Linux Mint the last time I checked, and i remember reading numerous articles about SYSRQ that mention that most distros ship with the feature disabled by default(Though not why they do that)

[–] Hiro8811@lemmy.world -2 points 9 months ago (1 children)

VLC?

[–] Artemis_Mystique@lemmy.ml 1 points 9 months ago (1 children)

No, MKV files have weird artifact issues for me so I use MPV(Celluloid) which mostly just works

[–] Hiro8811@lemmy.world -1 points 9 months ago (1 children)

Never had any problems, not even on Android and 4k video. I did turned on full hardware acceleration though

[–] Artemis_Mystique@lemmy.ml 1 points 9 months ago

my hardware struggles a lot and i find other odd quirks with VLC, I usually don't face such problems on MPV