With command strace, show that:
... poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}]) poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}]) poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}]) poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}]) poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}]) poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}]) poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}]) ...
With command strace, show that:
...
poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}])
poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}])
poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}])
poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}])
poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}])
poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}])
poll([{fd=3, events=POLLIN}, {fd=8, events=POLLIN}], 2, -1) = 1 ([{fd=8, revents=POLLNVAL}])
...