finding cpu usage with /proc

breadcrust · 06-09-2004, 04:20 AM

hi, im just wondering how i can find the cpu usage of a program (as a percentage or a figure i can turn into a percentage) using /proc file

thankx in advance

zaphod666 · 06-09-2004, 07:32 AM

Hi,

why don't use ps? It gives you all information about cpuusage, you can define the informations ps writes to stout, just read the manpage.

Bis Bald

Hko · 06-09-2004, 07:44 AM

I'm not very sure this is the most correct way, but from a little browsing through "man proc" I'd say something like:

- First get the PID of the process you want to get the CPU percentage of.
- Then parse /proc/<PID>/stat and get the fields "utime" and "stime" from that file.
- Add those two values and call the result "pidcpu", i.e.: pidcpu = utime + stime
- Parse /proc/stat and add the first 3 fields from the first line ("cpu") together, call this result "totalcpu"
- finally: percentage = 100 * pidcpu / totalcpu

breadcrust · 06-14-2004, 02:02 AM

hmm, thanx hko, but that doesnt seem to work.

i might end up using ps if i cant figure out how to do this through /proc. i had a quick look at the man page for ps but i couldnt figure out how to show cpu usages, how can this be done?

zaphod666 · 06-14-2004, 11:09 AM

Hi,

look for this in the manpage:

STANDARD FORMAT SPECIFIERS
These may be used to control both output format and sort-
ing.
For example: ps -eo pid,user,args --sort user

CODE HEADER
() ()

%cpu %CPU
%mem %MEM
alarm ALARM
args COMMAND
blocked BLOCKED
bsdstart START
bsdtime TIME
c C
caught CAUGHT

Bis Bald

Hko · 06-14-2004, 11:49 AM

Quote:

hmm, thanx hko, but that doesnt seem to work.

Sorry about that.

Quote:

i might end up using ps if i cant figure out how to do this through /proc. i had a quick look at the man page for ps but i couldnt figure out how to show cpu usages, how can this be done?

I'd try having a look at the source of 'ps' instead of the man page. 'ps' uses /proc for sure. You can get it here: http://procps.sourceforge.net/

mimithebrain · 06-17-2004, 04:54 PM

How, in c++, can I retrieve a specific PID cpu usage?
in C++
not bash

thanks

breadcrust · 06-17-2004, 11:08 PM

Quote:

Originally posted by mimithebrain
How, in c++, can I retrieve a specific PID cpu usage?
in C++ not bash

thats what im trying to figure out, using /proc files. this isnt a shell script im doing, its a tcl/tk application.

keefaz · 06-18-2004, 09:28 AM

hko is right, I don't see an other good solution than open virtual file /proc/<PID>/stat and analyse it ever in C++ or tcl/tk.

Try cat some of these files and you will see.

mimithebrain · 06-18-2004, 10:25 AM

That does not help,

What I need for my project (and his different project) is how to access that cpu/kernel filesystem and access this is C++,
If nobody knows, say so.
Like that ramdom number thing, I'll have to figure out a formula myself!

Well, can't get everything fresh baked on a plate without working for it!

keefaz · 06-18-2004, 10:41 AM

Well apparently you don't know read...I will add one more thing
/proc/<PID>/stat is a virtual file but you can open it for read like any regular file.

Hko · 06-18-2004, 01:27 PM

Quote:

Originally posted by mimithebrain
That does not help,

You didn't try.

Quote:

What I need for my project (and his different project) is how to access that cpu/kernel filesystem and access this is C++,

The answers in this thread were already referring to C(++).

Quote:

If nobody knows, say so.

If you don't know how to open a file in C(++)....say so, instead of re-asking the original question, which is quite a different from "how to read a file in C(++)?"

mimithebrain · 06-18-2004, 01:55 PM

by the quoting, I see I might have offended you.
Sorry, with sugar on it...

what would be the code to access and assimilate the infomation in /proc ?
When I attempt to read file in proc with "kwrite", it's blank.

Thank you

jim mcnamara · 06-18-2004, 03:01 PM

www.advancedlinuxprogramming.com has a chapter (pdf file) on working with the proc filesystem. It has example code in C.

Hko · 06-18-2004, 03:21 PM

Quote:

Originally posted by mimithebrain
by the quoting, I see I might have offended you.

True.

Quote:

what would be the code to access and assimilate the infomation in /proc

Basically:

Code:

#include <fstream>
#include <iostream>

#define MAXLEN 100

int main()
{
	 std::ifstream f;
	 char line[MAXLEN + 1];

	 f.open("/proc/stat");
	 f.get(line, MAXLEN);
	 std::cout << line << std::endl;
	 return 0;
}

Quote:

When I attempt to read file in proc with "kwrite", it's blank.

Some files in /proc may be empty, to other files you may have not persmission to read. But the files you need for cpu-usage will be readable by normal users. For example, /proc/self/stat should not be empty, and readable. If it is still empty, I can only think of only one other reason: your kernel does not support the /proc file-system, or it isn't mounted. This not very likely for the main linux distributions though.