Why C-forkbombs don't work like bash ones?

Question

If I run the classical bash forkbomb:

:(){ :&:&};: 

my system hangs after a few seconds.

I tried to write a forkbomb in C, here is the code:

#include <unistd.h>  int main( ) {     while(1) {         fork();     }     return 0; } 

When I run it the system gets less responsive, but I can kill that process (even after minutes) just pressing ^C.

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The above code is different from the original bash forkbomb I posted: it's something more like:

:( ) {     while true     do         :     done } 

(I didn't test it; don't know if it'd hang the system).

So I also tried to implement the original version; here the code:

#include <unistd.h>  inline void colon( const char *path ) {     pid_t pid = fork( );     if( pid == 0 ) {         execl( path, path, 0 );     } }  int main( int argc, char **argv ) {     colon( argv[0] );     colon( argv[0] );     return 0; } 

But still nothing: I can run it and then easily kill it. It's not hanging my system.

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Why?

What's so special about bash forkbombs? Is it because bash uses a lot more memory/CPU? Because bash processes call a lot more system calls (eg, to access filesystem) than mine?

Answer 1

That C program is tiny, seriously tiny. In addition, fork()'ing a program like that is very, very efficient. An interpreter, such as Bash, however, is much more expensive in terms of RAM usage, and needs to access the disk all the time.

Try running it for much longer. :)

Answer 2

The real cause for this is that in BASH the process you create is detached from the parent. If the parent process (the one you initially started) is killed, the rest of the processes live on. But in the C implementations you listed the child processes die if the parent is killed, so it's enough to bring down the initial process you started to bring down the whole tree of ever-forking processes.

I have not yet come up with a C forkbomb implementation that detaches child processes so that they're not killed if the parent dies. Links to such implementations would be appreciated.