Build a Simple Bash Script to Monitor CPU, Memory, and Disk Usage on Linux

Introduction

Monitoring system resources is essential for server administration, especially when deploying new applications. This guide shows how to write a Bash script that reports memory, disk, and CPU usage percentages in a three‑column format.

Memory Monitoring

The free -m command provides total and used memory. Using awk 'NR==2{printf "%.2f%%\t\t", $3*100/$2}' extracts the used‑memory percentage from the second line.

free -m

# free -m
total       used       free    shared  buffers  cached
Mem:        996        92       904        0       11       31
-/+ buffers/cache:        49       947
Swap:       1583        0      1583

Disk Monitoring

The df -h command reports filesystem usage. The following pipeline isolates the root partition and prints its usage percentage:

df -h | awk '$NF=="/"{printf "%s\t\t", $5}'

# df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root 14G  814M   12G   7% /
...

CPU Monitoring

Using top -bn1 in batch mode, we extract the load average and convert it to a percentage:

top -bn1 | grep load | awk '{printf "%.2f%%\t\t
", $(NF-2)}'

# top -bn1 | grep load
top - 19:31:25 up  1:47,  1 user,  load average: 0.00, 0.00, 0.00

Assembling the Script

Store each metric in a variable, then loop for a defined period (e.g., one hour) printing the values every few seconds.

#!/bin/bash
printf "Memory\t\tDisk\t\tCPU
"
end=$((SECONDS+3600))
while [ $SECONDS -lt $end ]; do
  MEMORY=$(free -m | awk 'NR==2{printf "%.2f%%\t\t", $3*100/$2}')
  DISK=$(df -h | awk '$NF=="/"{printf "%s\t\t", $5}')
  CPU=$(top -bn1 | grep load | awk '{printf "%.2f%%\t\t
", $(NF-2)}')
  echo "$MEMORY$DISK$CPU"
  sleep 5
done

Running the script prints lines such as:

Memory Disk CPU
9.34%   7%   0.00%

You can redirect the output to a log file with ./stats.sh >> log.txt.

Stress Testing (Optional)

Install the stress utility (e.g., yum install stress) and run a load test to generate CPU and memory pressure for an hour:

# stress -c 2 -i 1 -m 1 --vm-bytes 128M -t 3600s

While the stress test runs, the monitoring script continues to report resource usage, allowing you to observe system behavior under load.