Monitoring process memory/CPU usage with top and plotting it with gnuplot

If you want to monitor the memory and CPU usage of a particular Linux process for a few minutes, perhaps during a performance test, you can capture the data with top and plot them with gnuplot. Here is how:

Run this script (perhaps via nohup) to capture the data:

# Usage: ./ <PID of the process>
# Output: top.dat with lines such as `1539689171 305m 2.0`, i.e. unix time - memory with m/g suffix - CPU load in %
# To plot the output, see
export PID=$1
rm top.dat
while true; do top -p $PID -bMn 1 | egrep '^[0-9]+' | awk -v now=$(date +%s) '{print now,$6,$9}' >> top.dat; done

then plot them via ./ top.dat top.png:

#!/usr/bin/env gnuplot --persist -c
# Plot memory and CPU usage over time. Usage:
# <input file> [<output .png file>]
# where the input file has the columns `<unix time> <memory, with m/g suffix> <% cpu>`
# To create the input file, see

# Arguments:
set term x11
set title 'Memory, CPU usage from' . infile
set xdata time
set timefmt "%s"
set xlabel "Time [[hh:]mm:ss]"
set ylabel "Memory usage"
set format y '%.1s%cB'

set y2label 'CPU usage'
set format y2 '%.0s%%'
set y2tics nomirror
set tics out
set autoscale y
set autoscale y2

resolveUnit(u,mul,x)=(pos=strstrt(x,u), pos > 0 ? sprintf("%f",real(substr(x,1,pos - 1))*mul) : x)
if (exists("outfile") && strlen(outfile) > 0) {
    print "Outputting to the file ", outfile
    set term png # 640,480
    set output outfile

# Styling
set style line 1 linewidth 2 linecolor 'blue'
set style line 2 linecolor 'light-green'
#set xtics font ", 10"
set tics font ", 10"
set xtics rotate 60 # put label every 60s, make vertical so they don't clash in .png if too many

plot infile u 1:3 with lp axes x1y2 title "cpu" linestyle 2, \
    infile using 1:(check(stringcolumn(2))) with linespoints title "memory" linestyle 1
Published on System Code Geeks with permission by Jakub Holy, partner at our SCG program. See the original article here: Monitoring process memory/CPU usage with top and plotting it with gnuplot

Opinions expressed by System Code Geeks contributors are their own.

Jakub Holy

Jakub is an experienced Java[EE] developer working for a lean & agile consultancy in Norway. He is interested in code quality, developer productivity, testing, and in how to make projects succeed.
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