trace system calls and signals

-f          Trace child processes as they are created by currently traced processes as a result of
            the fork(2) system call.

            On non-Linux platforms the new process is attached to as soon  as  its  pid  is  known
            (through  the  return  value  of  fork(2) in the parent process). This means that such
            children may run uncontrolled for a while (especially in  the  case  of  a  vfork(2)),
            until  the  parent  is  scheduled again to complete its (v)fork(2) call.  On Linux the
            child is traced from its first instruction with  no  delay.   If  the  parent  process
            decides  to  wait(2) for a child that is currently being traced, it is suspended until
            an appropriate child process either terminates or incurs a signal that would cause  it
            to terminate (as determined from the child's current signal disposition).

            On SunOS 4.x the tracing of vforks is accomplished with some dynamic linking trickery.

-o filename Write  the  trace output to the file filename rather than to stderr.  Use filename.pid
            if -ff is used.  If the argument begins with `|' or with `!'  then  the  rest  of  the
            argument  is  treated  as a command and all output is piped to it.  This is convenient
            for piping the debugging output to a program without  affecting  the  redirections  of
            executed programs.