If you go... bash $ ulimit -u 10 $ /bin/true you get... bash: fork: retry: No child processes bash: fork: retry: No child processes bash: fork: retry: No child processes bash: fork: retry: No child processes bash: fork: Resource temporarily unavailable but "No child processes" is actually an error from wait(2), not from fork(2). This is because bash tries to reap children before printing the error. If that fails then you get whatever error wait(2) returned, but if it succeeds then isn't errno technically undefined at that point (although in practice on this system it keeps the error from wait(2))? Tested in: bash-4.3.42-3.fc23.x86_64
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This was fixed by rebasing bash to version 4.4 in rawhide.