I've found many posts on this website detailing how to find the usage of processes in linux, but most of these return the percent memory/cpu usage per process. I need to know the exact usage per process, as the results for the processes I'm interested in are always rounded down to zero.

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    Define exact? To what level? What is the specific problem you are trying to solve? which resources are you specifically interested in? Which version of Linux specifically distribution and version number.
    – mdpc
    May 10, 2014 at 20:35

1 Answer 1


Memory usage in a modern operating system with virtual memory and shared libraries is hard to define. Some things complicating things: Some of the memory of a process might:

  • not actually be in RAM, but be swapped out to disk
  • not yet be allocated, and only be allocated on first use
  • be shared with other processes
  • be a file on disk that is cached for efficiency reasons.
  • not be system memory, but memory of e.g. a network card.

Depending on whether you want to include/exclude the parts of the list above, you get different results:

  • RSS (Resident Set Size) in the amount of memory that that are actually in RAM for a process. This includes shared libraries, but excludes swapped out data.
  • VSZ (Virtual Size) is the total amount of memory, including the part that is swapped out.

Also see this quention: https://stackoverflow.com/questions/7880784/what-is-rss-and-vsz-in-linux-memory-management

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