Linux Server Troubleshooting With strace

“strace is a useful little utility – installed by default
on most Linux systems – which allows you to find out what a
program is doing under the hood by tracing the system calls it’s
making. strace is a great basic debugging tool; but it’s also
fascinating to use even when you’re not tracing a problem. It can
teach you a lot about how a Linux program works.

“A system call is a message from the program to the kernel. User
programs on a modern system run in a little sandbox: they’re not
permitted to interact directly with the computer (so you can’t just
shove numbers directly into registers to do things, as you could
back in the day). Instead, every time the program needs to interact
with the rest of the system, it sends a request (a system call) to
the kernel. strace tracks these messages. Do remember, then, that
if you don’t see any strace output for a while, it doesn’t
necessarily mean that your program is stuck. It might just be doing
something within its own sandbox that doesn’t require any
communication with the rest of the system.”

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