Quantify RAM, CPU use of a process in C under Linux

Question

How to find out, how much RAM and CPU "eats" certain process in Linux? And how to find out all runned processes (including daemons and system ones)? =)

UPD: using C language

Answer 1

Use top or ps .

For example, ps aux will list all processes along with their owner, state, memory used, etc.

EDIT: To do that with C under Linux, you need to read the process files in the proc filesystem. For instance, /proc/1/status contains information about your init process (which always has PID 1 ):

char buf[512];
unsigned long vmsize;
const char *token = "VmSize:";
FILE *status = fopen("/proc/1/status", "r");
if (status != NULL) {
    while (fgets(buf, sizeof(buf), status)) {
        if (strncmp(buf, token, strlen(token)) == 0) {
            sscanf(buf, "%*s %lu", &vmsize);
            printf("The INIT process' VM size is %lu kilobytes.\n", vmsize);
            break;
        }
    }
    fclose(status);
}

Answer 2

Measuring how much ram a process uses is nearly impossible. The difficulty is, that each piece of ram is not used by exactly one process, and not all ram a process is using is actually "owned" by it.

For example, two processes can have shared mappings of the same file, in which case any pages which are in core for the mapping, would "belong" to both processes. But what if only one of these processes was using it?

Private pages can also be copy-on-write if the process has forked, or if they have been mapped but not used yet (consider the case where a process has malloc'd a huge area but not touched most of it yet). In this case, which process "owns" those pages?

Processes can also be effectively using parts of the buffer cache and lots of other kinds of kernel buffers, which aren't "owned" by them.

---

There are two measurements which are available, which are VM Size, (how much memory the process has mapped just now) and resident set size (RSS). Neither of them really tells you much about how much memory a process is using, because they both count shared pages and neither counts non-mapped pages.

So is there an answer? Some of these can be measured by examining the page maps structures which are now available in /proc (/proc/pid/pagemap), but there isn't necessarily a trivial way of sharing out the "ownership" of shared pages.

See Linux's Documentation/vm/pagemap.txt for a discussion of this.