2d ago

cat /proc/sys/kernel/random/uuid

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.

❤️🐧

33 comments

boot_id seems to be static, probably set at boot.
So don't use it for a random uuid.
- it's fine as long as you reboot before each call
- Oops you’re correct. Editing OP.

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

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.
- 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:
  txt
  
  -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

I’ve used this in some bash scripts, very useful!
- That's what I mean. No more searching for ways to create shell-friendly randomness ($RANDOM does not always cut it).

Thank you so much for sharing this!

This is awesome. Thank you

Works in Termux on Android

Interesting,
non-scientific speed test:

kernel 6.1.0-37-amd64:

 shell

    
$ 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:

 shell

    
$ 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).

See also: /dev/null
It’s basically a black hole where you can throw anything.
- Yes, but what if it were a subscription? May I present: /dev/null-as-a-Service.
  
  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.
- cat /proc/sys/kernel/random/uuid > /dev/null
  
  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
  
  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.
  
  no.
  
  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.
  
  while :; do cat /proc/sys/kernel/random/uuid > /dev/null; done
  edit: on all cores for maximum "efficiency"

33 comments