output overwritten with the -ff option when the pid rolls over the pix_max (and you have many processes)

[Philippe Ombredanne]

This is a bug that can happen rarely, but is easy to reproduce.
If you trace forks with -ff and -o and you have more processes created
than the maximum number of pids, eventually the saved traces of some
pids will be overwritten

The simple workaround is to increase the pid max.
32768 is the typical default value on most Linux installations. It can
be increased to 4194303 which is the highest
supported value on 32 bit systems and should be high enough for many use cases.
    $ echo 4194303 > /proc/sys/kernel/pid_max

This is still a bug though and the output should not be overwritten IMHO

-- 
Philippe Ombredanne