Guides

How to Write a Bash Script for Server Health and Disk Alerts

By Ravindra Bagale, DevOps trainer · LinkedIn · Published: 28 October 2026 · Last updated: 28 October 2026

Write a Bash health script that checks CPU, memory and disk, prints a report, and can alert — the junior task Capgemini and Wipro-style teams still assign.

Language: English · मराठी · हिंदी

Why write a health script

Waiting for users in Mumbai or Frankfurt to report a full disk is too late. A five-minute Bash check is the first DevOps automation many teams trust.

Why: Catch pressure before outage. What: Bash script: metrics, thresholds, report, optional alert. How: Build pieces below on Amazon Linux or Ubuntu.

Concept 1: Safe script skeleton

Why: Broken scripts with set +u catch mistakes early. What: shebang, set -euo pipefail, chmod 700. How: Start every ops script this way.

Example 1: Shebang and safe mode

Type this:

printf '%s\n' '#!/usr/bin/env bash' 'set -euo pipefail' > /tmp/health.sh
head -2 /tmp/health.sh

You will see:

#!/usr/bin/env bash
set -euo pipefail

What it means: set -euo pipefail stops on errors and unset vars.

Example 2: Disk percent function

Type this:

python3 -c "u=91; print('ALERT' if u>=90 else 'ok')"

You will see:

ALERT

What it means: Threshold logic before any webhook.

Example 3: chmod private

Type this:

chmod 700 /tmp/health.sh
stat -c %a /tmp/health.sh 2>/dev/null || stat -f %A /tmp/health.sh

You will see:

700

What it means: Never world-writable scripts.

Concept 2: Collect CPU memory disk

Why: You cannot alert on vibes. What: /proc/stat, /proc/meminfo, df -P. How: Parse stable columns.

Example 4: CPU from /proc

Type this:

grep '^cpu ' /proc/stat | awk '{print \$2}'

You will see:

... idle ticks ...

What it means: /proc/stat feeds CPU math on Linux.

Example 5: Memory available

Type this:

awk '/MemAvailable/ {print \$2}' /proc/meminfo

You will see:

2048123

What it means: Values are kB. Convert for humans.

Example 6: Disk use awk

Type this:

df -P / | awk 'NR==2 {print \$5}'

You will see:

39%

What it means: Use df -P for stable columns.

Concept 3: Report and exit codes

Why: Cron and monitoring read exit codes. What: Write a report file; exit 0/2. How: Dry-run webhooks with fake URLs.

Example 7: Report file

Type this:

printf '%s\n' 'host=lab' 'disk=39%' 'mem_ok=yes' > /tmp/health-report.txt
cat /tmp/health-report.txt

You will see:

host=lab
disk=39%
mem_ok=yes

What it means: Reports beat silent scripts.

Example 8: Exit codes

Type this:

python3 -c "import sys; sys.exit(2)" ; echo exit=\$?

You will see:

exit=2

What it means: Non-zero exits drive cron alerts.

Example 9: Webhook dry-run

Type this:

printf '%s\n' 'POST https://hooks.example.invalid/alert' 'body={text: disk 91%}'

You will see:

POST https://hooks.example.invalid/alert
body={text: disk 91%}

What it means: Use a fake URL in labs; never commit real secrets.

Concept 4: Schedule and harden

Why: A script that never runs helps nobody. What: cron every 5 minutes; absolute paths. How: Log redirects; bash -n first.

Example 10: Cron line draft

Type this:

printf '%s\n' '*/5 * * * * /home/ec2-user/bin/health.sh >> /var/log/health.log 2>&1'

You will see:

*/5 * * * * /home/ec2-user/bin/health.sh >> /var/log/health.log 2>&1

What it means: Redirect stdout and stderr.

Example 11: PATH reminder

Type this:

printf '%s\n' 'Use absolute paths in cron' '/usr/bin/df not df'

You will see:

Use absolute paths in cron
/usr/bin/df not df

What it means: Cron has a tiny PATH.

Example 12: Test once

Type this:

bash -n /tmp/health.sh && echo SYNTAX_OK

You will see:

SYNTAX_OK

What it means: bash -n checks syntax without running.

Minimal script shape

1. shebang + set -euo pipefail
2. read disk percent
3. if >= 90 then exit 2 and message
4. else write OK report
5. cron with >> log 2>&1

Suppose: Hyderabad e-commerce box

Disk hits 92 percent before Big Billion days. Script pages Slack-style webhook.

Suppose: Berlin SaaS VM

Memory Available drops. Same script pattern, different threshold.

Check yourself (quiz)

Skeleton → metrics → thresholds → report → cron. Mode 700. No secrets. Did you understand? Let us try it once more.