Master Essential Linux Shell Scripts for System Monitoring and Automation

Precautions

1) Add interpreter at the top: #!/bin/bash

2) Use four spaces for indentation; add plenty of comments.

3) Naming conventions: uppercase for constants, lowercase for local variables, lowercase for functions, names should reflect purpose.

4) Variables are global by default; use local inside functions to limit scope.

5) Two commands help debugging: set -e exits on non‑zero status, set -x prints each command.

6) Test scripts thoroughly before deploying to production.

1. Generate Random Strings or Numbers

Generate a random 8‑character string:

Generate a random 8‑digit number:

cksum

prints CRC checksum and byte count.

2. Define a Color Output Function

Use the function keyword to define a function, with or without the keyword.

3. Batch Create Users

4. Check If a Package Is Installed

5. Check Service Status

6. Verify Host Liveness

Method 1: Put erroneous IPs into an array and consider a host down after three failed pings.

Method 2: Store failure count in a FAIL_COUNT variable and treat three failures as down.

Method 3: Use a for loop that breaks on a successful ping; otherwise report failure.

7. Monitor CPU, Memory, and Disk Utilization

CPU: Use vmstat to analyze CPU statistics.

Memory:

Disk:

8. Batch Host Disk Utilization Monitoring

Prerequisite: password‑less SSH or key‑based login between monitoring and target hosts.

Create a configuration file containing host IP, user, and port.

9. Check Website Availability

1) Verify URL reachability.

2) Test URL three times; the logic mirrors host liveness checking.

These shell script examples are practical and frequently appear in interview questions; hands‑on practice is essential rather than copying and pasting code.