Build a Bash Script to Monitor Memory, Disk, and CPU in Real Time

Monitoring the environment is essential for server operations, especially when deploying new applications. While many open‑source tools exist for continuous monitoring, a simple Bash script can be used for short‑term testing.

The script outputs a three‑column table showing the percentage of memory, disk, and CPU usage on the host.

1. Monitor Memory

free -m | awk 'NR==2{printf "%.2f%%\t\t", $3*100/$2 }'

The free -m command displays total and used memory; awk extracts the second line and calculates used memory as a percentage of total.

2. Monitor Disk

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

df -h

reports filesystem usage; the awk filter selects the line where the mount point is / and prints the usage column.

3. Monitor CPU

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

top -bn1

runs top in batch mode for a single iteration; grep load extracts the line containing the load average, and awk prints the load value as a percentage.

These commands are stored in variables:

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)}')

A while loop runs for a defined period (e.g., one hour), printing the three values every five seconds.

end=$((SECONDS+3600))
while [ $SECONDS -lt $end ]; do
  echo "$MEMORY$DISK$CPU"
  sleep 5
done

The complete script is:

#! /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\t\tDisk\t\tCPU
9.34%\t7%\t0.00%
9.34%\t7%\t0.00%
...

Output can be redirected to a log file for later analysis.

Stress Test

To generate load, install the stress utility (e.g., yum install stress) and run: stress -c 2 -i 1 -m 1 --vm-bytes 128M -t 3600s This creates two CPU‑intensive processes, one I/O‑intensive process, and one memory allocator process for one hour, allowing you to observe how the monitoring script reports increased resource usage.

The tutorial ends here, providing a simple yet useful Bash script for system administrators.