$ strace -o /tmp/strace_su.out -tt -f su
strace_su.out in attachment ; command hangs at '2571952 10:49:47.809422 ppoll([{fd=5, events=POLLIN}], 1, {tv_sec=24, tv_nsec=999930000}, NULL, 8'
$ strace -o /tmp/strace_su.out -tt -f su
strace_su.out in attachment ; command hangs at
'2571952 10:49:47.809422 ppoll([{fd=5, events=POLLIN}], 1, {tv_sec=24, tv_nsec=999930000}, NULL, 8'