strace is a system call tracer, i.e. a debugging tool which prints out a trace
of all the system calls made by a another process/program.

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: https://sourceforge.net/projects/strace/