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Similar to question How to log CPU load?, I would like to log memory of a process.

The process I want to log, is killed on a remote server, and I want to find out the CPU load and the memory usage just before it was killed.

[update]

Both Stefano Palazzo's neat little python script and

Michał's one line output values that are smaller than in top for CPU and Mem. Do you have an idea why?

output top:

 PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND 
2312 schXX     20   0 1241m 328m  58m S  100  0.3  11:56.68 MATLAB 

output Stefano Palazzo's python script:

python memlogger.py 2312
%CPU    %MEM
76.00   0.20
76.00   0.20
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I unfortunately can't comment here yet but you may find this post of interest expalining why ps may differ from top: stackoverflow.com/questions/131303/… – P-M Jul 4 at 12:30

You can create one-liner in shell:

logpid() { while sleep 1; do  ps -p $1 -o pcpu= -o pmem= ; done; }

to log process with pid=123 just:

logpid 123

or to see and write log to file:

logpid $$ | tee /tmp/pid.log

If you want other data to be logged, modify -o {this} options. See man ps section "STANDARD FORMAT SPECIFIERS" for available parameters to use. If you want different time resolution, change sleep {this} in function logpid().

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If you are precisely after the top statistics you could run top in batch mode specifying the pid of the process that you are after. Taking the example from this page (http://www.dedoimedo.com/computers/linux-cool-hacks.html) if you typed

top -b -d 10 -n 3 >> top-file

You would "have top running in batch mode (-b). It's going to refresh every 10 seconds, as specified by the delay (-d) flag, for a total count of 3 iterations (-n). The output will be sent to a file." Including -p you can specify the pid of the process that you are after. This will of course return more than purely cpu and ram but it will contain thos fields. In my case for example I would get the following when monitoring pid 9189 using top -b -d 10 -n 3 -p 9189 >> ~/top-file:

PID  USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
9189 pmj27     20   0 1617016 808112  27916 S   0.0  0.3   1:36.63 gedit
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This page, though it doesn't do redirections to a file, does carry out some more sophisitcated modifications allowing you to obtain only CPU printed out. If you someone knows of a good way to redirect the output to a file and have it update periodically I'd be interested to know. watch doesn't seem ideal to me for this: superuser.com/questions/281347/filtering-top-command-output – P-M Jul 4 at 15:29

This simple python script should do what you want:

import time
import string
import sys
import commands

def get_cpumem(pid):
    d = [i for i in commands.getoutput("ps aux").split("\n")
        if i.split()[1] == str(pid)]
    return (float(d[0].split()[2]), float(d[0].split()[3])) if d else None

if __name__ == '__main__':
    if not len(sys.argv) == 2 or not all(i in string.digits for i in sys.argv[1]):
        print("usage: %s PID" % sys.argv[0])
        exit(2)
    print("%CPU\t%MEM")
    try:
        while True:
            x = get_cpumem(sys.argv[1])
            if not x:
                print("no such process")
                exit(1)
            print("%.2f\t%.2f" % x)
            time.sleep(0.5)
    except KeyboardInterrupt:
        print
        exit(0)

You first need to find out the process id of the program you want to monitor, then you can run the script with the PID as an argument:

python log.py 3912

It will print the cpu usage and ram usage in per cent two times a second:

%CPU    %MEM
0.90    0.40
1.43    0.40
8.21    0.40
...

You can then redirect its output to a file in order to import it into a spreadsheet later (python log.py 9391 > firefox_log.txt) and import the data into a spreadsheet selecting Tab as your separator.

The program quits when you hit Ctrl+C or when the process is killed.

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Dear Stefano, thank you very much for your script. Unfortunately it seems to output wrong results. Do you have any idea why? Please see my updated question. – Framester Aug 8 '11 at 12:25

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