this post was submitted on 24 May 2025
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cat /proc/sys/kernel/random/uuid [I ❤️ Linux] (feddit.org)
submitted 1 day ago* (last edited 12 hours ago) by A_norny_mousse@feddit.org to c/linux@programming.dev
33 comments fedilink hide all child comments
 

That's all. I just found this in a random script. Generates a random UUID every time it's called. I didn't know.

Of course I can also use uuidgen or pipe /dev/(u)random into something to get a random alphanumeric string - but this is built right into the kernel!

In /proc/sys/kernel/random/, there's also boot_id which ~~seems to do the same~~ is static, and some tweakable parameters.

❤️🐧

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[–] lnxtx@feddit.nl 2 points 8 hours ago* (last edited 8 hours ago)

Interesting,
non-scientific speed test:

kernel 6.1.0-37-amd64:

$ time for i in $(seq 1 100000); do cat /proc/sys/kernel/random/uuid > /dev/null; done

real    3m53,388s
user    1m37,366s
sys     2m13,847s

$ for i in $(seq 1 100000); do cat /proc/sys/kernel/random/uuid ; done | wc -l
100000

vs. uuid 1.6.2-1.5+b11:

$ time for i in $(seq 1 100000); do uuid -v4 > /dev/null; done

real    4m44,854s
user    1m37,867s
sys     3m4,414s

$ for i in $(seq 1 100000); do uuid -v4 ; done | wc -l
100000

EDIT: I'm blind (wrong result).

[–] timhh@programming.dev 8 points 1 day ago (1 children)

Yeah but please don't actually use this. Use a proper UUID library that works cross-platform and lets you choose the UUID type and can be seeded etc.

[–] A_norny_mousse@feddit.org 2 points 12 hours ago* (last edited 12 hours ago)

Can you explain?
Use for what?
Also it is being seeded, according to the file urandom_min_reseed_secs which is also writeable. Here are the other files:

-r--r--r-- 1 root root 0 25. 5. 11:13 boot_id
-r--r--r-- 1 root root 0 25. 5. 11:19 entropy_avail
-r--r--r-- 1 root root 0 25. 5. 11:19 poolsize
-rw-r--r-- 1 root root 0 25. 5. 11:19 urandom_min_reseed_secs
-r--r--r-- 1 root root 0 25. 5. 11:19 uuid
-rw-r--r-- 1 root root 0 25. 5. 11:19 write_wakeup_threshold

edit: the type is always DCE/random

[–] bleistift2@sopuli.xyz 13 points 1 day ago (1 children)

That’s what you get when you define a file system as “a system that names things”.

[–] Redjard@lemmy.dbzer0.com 16 points 1 day ago (2 children)

boot_id seems to be static, probably set at boot.
So don't use it for a random uuid.

[–] nibbler@discuss.tchncs.de 4 points 12 hours ago

it's fine as long as you reboot before each call

[–] A_norny_mousse@feddit.org 1 points 12 hours ago

Oops you’re correct. Editing OP.

[–] notfromhere@lemmy.ml 6 points 1 day ago (1 children)

I’ve used this in some bash scripts, very useful!

[–] A_norny_mousse@feddit.org 2 points 12 hours ago* (last edited 12 hours ago)

That's what I mean. No more searching for ways to create shell-friendly randomness ($RANDOM does not always cut it).

[–] clif@lemmy.world 5 points 1 day ago

This is awesome. Thank you

[–] pelya@lemmy.world 4 points 1 day ago

Works in Termux on Android

[–] kionite231@lemmy.ca 5 points 1 day ago

Thank you so much for sharing this!

[–] Hamartiogonic@sopuli.xyz -2 points 1 day ago (2 children)

See also: /dev/null

It’s basically a black hole where you can throw anything.

[–] DaPorkchop_@lemmy.ml 10 points 1 day ago (1 children)

Yes, but what if it were a subscription? May I present: /dev/null-as-a-Service.

[–] A_norny_mousse@feddit.org 1 points 7 hours ago

The most secure Bitcoin endpoint yet!

lol.

Okay, let’s be honest, it’s basically a crappy Pentium 4 box with Debian and nginx installed.

[–] victorz@lemmy.world 8 points 1 day ago* (last edited 14 hours ago) (5 children) 
cat /proc/sys/kernel/random/uuid > /dev/null
[–] A_norny_mousse@feddit.org 1 points 12 hours ago* (last edited 12 hours ago)

while :; do cat /proc/sys/kernel/random/uuid > /dev/null; done

edit: on all cores for maximum "efficiency"

[–] DaPorkchop_@lemmy.ml 16 points 1 day ago (4 children)

Would have to be cat /proc/sys/kernel/random/uuid > /dev/null

You can't pipe to a file, only to programs, and since /dev/null isn't an executable your command will simply give an error.

To make it more clear, consider using dd, which lets you explicitly specify an input and output file. For example: dd if=/proc/sys/kernel/random/uuid of=/dev/sda1 wait shit that wasn't the right output oh god oh fu

[–] Redjard@lemmy.dbzer0.com 2 points 12 hours ago

dd is just cp but more confusing here.
The only thing dd can do that cp can't is stop ahead of time, which only really matters for infinite files like /dev/random

cp /proc/sys/kernel/random/uuid /dev/sda

[–] A_norny_mousse@feddit.org 1 points 12 hours ago

dd if=/proc/sys/kernel/random/uuid of=/dev/sda1

Peanuts. Real men do dd if=/proc/sys/kernel/random/uuid of=/dev/sda

[–] victorz@lemmy.world 1 points 14 hours ago* (last edited 14 hours ago)

Thanks, I'm overworked lately.

lol, the last part

[–] sixtoe@lemmy.blahaj.zone 2 points 1 day ago

i saw this and came to do THE THING but you beat me too it. GOOD ANYA

[–] henfredemars@infosec.pub 3 points 1 day ago (1 children)

The information will be evenly distributed upon its surface and some believe one day it will be be radiated back out into the rest of the system.

[–] Hamartiogonic@sopuli.xyz 2 points 1 day ago

That's a horrifying concept. Better not think about it.

[–] Hamartiogonic@sopuli.xyz 1 points 1 day ago (3 children)

That reminds me of the CPU stress test I ran many years ago.

dd if=/dev/random of=/dev/null

If you have 8 cores, just open 8 terminals, and run that code in each of them.

[–] victorz@lemmy.world 1 points 14 hours ago (1 children)

Can you guarantee that each process will run on its own core?

[–] Hamartiogonic@sopuli.xyz 2 points 13 hours ago

Absolutely not, quite the opposite actually. However, the end result is close to 100% CPU load, which is good enough for some purposes. Let’s say you want to test the performance of your CPU cooler, or overclock stability, this should good enough. There are also dedicated tools for people with more advanced needs.

[–] YerbaYerba@lemm.ee 4 points 1 day ago

/dev/urandom should stress the CPU more. /dev/random can be entropy limited

[–] lime@feddit.nu 2 points 1 day ago* (last edited 1 day ago) (1 children) 
for i in {1..n}  # where n == number of cores
do
  dd if=/dev/urandom of=/dev/null &
done

# to stop:
jobs -p | xargs kill
[–] Hamartiogonic@sopuli.xyz 1 points 13 hours ago (1 children)

Oh yeah. This looks like a much better way to do it. My solution is pretty bare bones by comparison.

[–] lime@feddit.nu 1 points 13 hours ago

the advantage of yours is that you can actually see the performance number afterwards.