Strace is a process tracer, i.e. a debugging tool that prints out
a trace of all the system calls made and signals received by a
process itself or a process and its descendants.

Strace is similar to the native BSD ``truss'' utility, but it's
output style is more convenient in most cases.

For strace to work, procfs has to be mounted. FreeBSD does not
mount it by default. For more information, man procfs.

WWW: http://sourceforge.net/projects/strace/