How can I measure the actual memory usage of an application or process?

Question

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How do you measure the memory usage of an application or process in Linux?

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Answer 1

Get Valgrind. Give it your program to run, and it'll tell you plenty about its memory usage.

This would apply only for the case of a program that runs for some time and stops. I don't know if Valgrind can get its hands on an already-running process or shouldn't-stop processes such as daemons.