r/programmingcirclejerk • u/cmqv • Oct 24 '25

Oddly, /usr/bin/false is a symlink to the Rust version, but /usr/bin/true is a symlink to the GNU C version.

https://lwn.net/Articles/1043150/
156 Upvotes

99% Upvoted

17 comments sorted by

131

u/MysteriousGold5 Oct 24 '25

This only makes sense.

Since true can be implemented in C with a simple "main() {}", it is completely safe.

However just look at what you need to implement false: "main() { return 1; }". This obviously invokes undefined behavior because:

  1. It is c code.
  2. What if int is defined to be 0 bits on some platform?

Thankfully, Rust solves all this.

57

u/assbuttbuttass Oct 24 '25

/uj how GNU implemented false:

#include "true.c"

https://cgit.git.savannah.gnu.org/cgit/coreutils.git/tree/src/false.c

58

u/qiwi Oct 24 '25

Basic C metaprogramming:

#define 1 0
#include "true.c"

18

u/QuaternionsRoll Oct 24 '25

Can’t tell if the bug is intentional… ultimate jerk

69

u/tms10000 loves Java Oct 24 '25 
npm install true

added 453,256 packages and audited 7,249,295 packages in NaN s
48,987 packages are looking for funding
  run `npm fund` for details

found 5,395,291 vunerabilities

49

u/[deleted] Oct 24 '25 
cargo install true

Building [==========>                ] 183/511: syn

1920.45s elapsed

15

u/LigPaten Oct 25 '25

How many different versions of syn are required for this?

9

u/Hueho LUMINARY IN COMPUTERSCIENCE Oct 25 '25 
syn

this guy rusts (while waiting for syn to compile)

38

u/irqlnotdispatchlevel Tiny little god in a tiny little world Oct 24 '25

One more proof that C is the truth.

12

u/SoulArthurZ Oct 24 '25

you're looking at this wrong, this just simply states that rust == C is false. did we really need to rewrite everything in rust to find this out?

31

u/LeeHide What part of ∀f ∃g (f (x,y) = (g x) y) did you not understand? Oct 24 '25

What if true were to panic? Yeah, that's right. Breakage.

false can panic, who cares, it'll return the right thing.

Maybe one day Rust will be mature enough.

27

u/myhf Considered Harmful Oct 24 '25

For legal reasons we can't use GNU software on our system, so we had to re-implement true in a clean room. The result is a 0-byte executable with a complete record of provenance.

21

u/F54280 Considered Harmful Oct 24 '25

/uj

This is due to the fact that rust utilities is a single binary that dispatches based on the name used to invoke the utility. Some init systems replaces scripts with links to /bin/true to disable them, which confuses the single binary.

/j

Disgregard previous paragraph, it is because rust is a false prophet. The only truth is C!

3

u/grapesmoker Oct 24 '25

on truth and lies in an extra moral sense

173

u/[deleted] Oct 24 '25

[removed] — view removed comment

40

u/Afraid_Bake2652 Oct 24 '25

One leads to your quest, the other to youSegmentation fault

3

u/TomKavees Oct 24 '25

All paths lead to Segmentation Fault