$ ./locktest & sleep 4; ./locktest [1] 1553 Using flock()... 1553 shares. 1553 owns 1553 shares Using flock()... 1557 shares. 1557 waiting for previous instance(s) to exit... 1553 owns 1557 owns Running... 1557 owns 1553 can't revert self lock to shared: Resource temporarily unavailable 1557 shares ^C [1]+ Exit 11 ./locktest