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.