I wrote a simple script to reproduce this: var text = ""; for (var i = 1; i <= 10; i++) { text += "Test line #" + i + "\n"; } var startTime = new Date(); for (i = 1; i < 100000; i++) { var exitCode = runMongoProgram("echo", text); assert.eq(0, exitCode); assert.neq("", rawMongoProgramOutput(), "got an exit code but there's no output"); clearRawMongoProgramOutput(); var remainingText = rawMongoProgramOutput(); if (remainingText !== "") { var timeTaken = (new Date() - startTime) / 1000; var msg = "still text remaining!\ntook "+i+" tries and "+timeTaken+" seconds\ntext remaining: '"+remainingText+"'"; assert(false, msg); } } Saving that script to a file and running it with the mongo shell eventually fails: assert failed : still text remaining! took 15648 tries and 38.383 seconds text remaining: 'sh51568| Test line #3 ' I have seen it fail in the same way in as little as one second. It has also failed occasionally on the line which asserts that the echo produces some output after it has exited.