A system call tracer

 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.
 The program to be traced need not be recompiled for this, so you can
 use it on binaries for which you don't have source.
 .
 System calls and signals are events that happen at the user/kernel
 interface. A close examination of this boundary is very useful for bug
 isolation, sanity checking and attempting to capture race conditions.