Monitoring and Plotting Process Memory/CPU Usage With top and 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. Keep reading to learn how.

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

#!/bin/sh
# Usage: ./monitor-usage.sh <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 https://gist.github.com/jakubholynet/931a3441982c833f5f8fcdcf54d05c91
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 the data via ./usage-plot.gp top.dat top.png:

#!/usr/bin/env gnuplot --persist -c
# Plot memory and CPU usage over time. Usage:
#  usage-plot.gp <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 https://gist.github.com/jakubholynet/931a3441982c833f5f8fcdcf54d05c91

# Arguments:
infile=ARG1
outfile=ARG2
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)
resolveUnits(x)=(resolveUnit("g",1024*1024*1024,resolveUnit("m",1024*1024,x)))
check(x)=(real(resolveUnits(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