Both strace and ltrace are powerful command-line tools for debugging and troubleshooting programs on Linux: Strace captures and records all system calls made by a process as well as the signals received, while ltrace does the same for library calls.
If a program acts differently than you expect, you can use these tools to see “behind the curtain” and maybe get some clues as to what is going on.
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Be forewarned, though. When you use either of these commands, you will end up with a lot of output to look through. Still, that can tell you quite a bit about how a process is working and sometimes give you important insights.
Source:: Network World – Linux