This is cute! It’s worth pointing out that strace ships a similar feature (-e fault) which works for any syscall, even if the binary is statically linked. It works using ptrace, which is lower level than LD_PRELOAD. Although -e fault doesn’t support probabilistic failure, it does provide a flexible way to target specific invocations of a syscall. For example, to fail every second fork() call: -e fault=fork,errno=ENOMEM,when=1+2.
Of course, typing this on my phone, I didn't get the syntax exactly right. Sorry! The actual strace argument should be
-e fault=clone:error=ENOMEM:when=1+2
First, modern glibc doesn't use the `fork` syscall directly; it uses clone() instead, so you have to fault clone to see anything happen on a glibc-based system. Second, I botched the syntax, oops!
For practical use, you probably want something like this:
This faults both clone and write at different rates (try it, the results are sort of funny), sets strace to only count events (reducing its overhead), and then suppresses the count printout at the end. Might be fun to use as a prank login shell if you want someone to think their machine is broken :)
