Essential Bash Scripts for System Monitoring and Automation

This article provides a toolbox of reusable Bash scripts aimed at common Linux operations and monitoring tasks.

General Guidelines

Start scripts with the interpreter line #!/bin/bash.

Use four spaces for indentation and add comments to explain each step.

Variable naming convention: uppercase for global constants, lowercase for locals, function names in lowercase describing their purpose.

Variables are global by default; use local inside functions to avoid scope pollution.

Debugging helpers: set -e to abort on non‑zero exit codes and set -x to trace command execution.

Always test scripts in a safe environment before deploying to production.

1. Generate Random Strings or Numbers

Three methods are shown for an 8‑character random string:

# echo $RANDOM | md5sum | cut -c 1-8
# openssl rand -base64 4
# cat /proc/sys/kernel/random/uuid | cut -c 1-8

For an 8‑digit random number:

# echo $RANDOM | cksum | cut -c 1-8
# openssl rand -base64 4 | cksum | cut -c 1-8
# date +%N | cut -c 1-8

cksum

prints the CRC checksum and byte count.

2. Colored Output Function

A reusable function echo_color prints text in green or red using ANSI escape codes. Two implementations are provided – an if/elif version and a case version.

function echo_color() {
    if [ "$1" == "green" ]; then
        echo -e "[32;40m$2[0m"
    elif [ "$1" == "red" ]; then
        echo -e "[31;40m$2[0m"
    else
        echo "Usage: echo_color red|green string"
    fi
}

3. Batch Create Users

#!/bin/bash
DATE=$(date +%F_%T)
USER_FILE=user.txt

# Backup existing file
if [ -s "$USER_FILE" ]; then
    mv "$USER_FILE" "${USER_FILE}-${DATE}.bak"
    echo_color green "${USER_FILE} exists, renamed to ${USER_FILE}-${DATE}.bak"
fi

echo -e "User\tPassword" >> "$USER_FILE"
echo -e "----------------" >> "$USER_FILE"

for USER in user{1..10}; do
    if ! id "$USER" &>/dev/null; then
        PASS=$(echo $RANDOM | md5sum | cut -c 1-8)
        useradd "$USER"
        echo "$PASS" | passwd --stdin "$USER" &>/dev/null
        echo -e "$USER\t$PASS" >> "$USER_FILE"
        echo "$USER User create successful."
    else
        echo_color red "$USER User already exists!"
    fi
done

4. Check If a Package Is Installed

#!/bin/bash
if rpm -q sysstat &>/dev/null; then
    echo "sysstat is already installed."
else
    echo "sysstat is not installed!"
fi

5. Verify Service Status

#!/bin/bash
PORT_C=$(ss -anu | grep -c 123)
PS_C=$(ps -ef | grep ntpd | grep -v grep)
if [ $PORT_C -eq 0 -o $PS_C -eq 0 ]; then
    echo "Content" | mail -s "Subject" [email protected]
fi

6. Host Liveness Check (Ping)

Three approaches are illustrated: using an array of error IPs, a counter variable, and a function that returns on success.

# Example using an array
IP_LIST="192.168.18.1 192.168.1.1 192.168.18.2"
for IP in $IP_LIST; do
    NUM=1
    while [ $NUM -le 3 ]; do
        if ping -c 1 $IP &>/dev/null; then
            echo "$IP Ping is successful."
            break
        else
            FAIL_COUNT[$NUM]=$IP
            let NUM++
        fi
    done
    if [ ${#FAIL_COUNT[*]} -eq 3 ]; then
        echo "${FAIL_COUNT[1]} Ping is failure!"
        unset FAIL_COUNT[*]
    fi
done

7. CPU, Memory, and Disk Utilization Monitoring

CPU

#!/bin/bash
DATE=$(date +%F_%H:%M)
IP=$(ifconfig eth0 | awk -F '[ :]+' '/inet addr/{print $4}')
MAIL="[email protected]"
if ! which vmstat &>/dev/null; then
    echo "vmstat command not found, please install procps package."
    exit 1
fi
US=$(vmstat | awk 'NR==3{print $13}')
SY=$(vmstat | awk 'NR==3{print $14}')
USE=$((US+SY))
if [ $USE -ge 50 ]; then
    echo -e "Date: $DATE
Host: $IP
Problem: CPU utilization $USE" | mail -s "CPU Monitor" $MAIL
fi

Memory

#!/bin/bash
DATE=$(date +%F_%H:%M)
IP=$(ifconfig eth0 | awk -F '[ :]+' '/inet addr/{print $4}')
MAIL="[email protected]"
TOTAL=$(free -m | awk '/Mem/{print $2}')
USE=$(free -m | awk '/Mem/{print $3-$6-$7}')
FREE=$((TOTAL-USE))
if [ $FREE -lt 1024 ]; then
    echo -e "Date: $DATE
Host: $IP
Problem: Total=$TOTAL, Use=$USE, Free=$FREE" | mail -s "Memory Monitor" $MAIL
fi

Disk

#!/bin/bash
DATE=$(date +%F_%H:%M)
IP=$(ifconfig eth0 | awk -F '[ :]+' '/inet addr/{print $4}')
MAIL="[email protected]"
TOTAL=$(fdisk -l | awk -F '[: ]+' 'BEGIN{OFS="="}/^Disk \/dev/{printf "%s=%sG,",$2,$3}')
PART_USE=$(df -h | awk 'BEGIN{OFS="="}/^\/dev/{print $1,int($5),$6}')
for i in $PART_USE; do
    PART=$(echo $i | cut -d"=" -f1)
    USE=$(echo $i | cut -d"=" -f2)
    MOUNT=$(echo $i | cut -d"=" -f3)
    if [ $USE -gt 80 ]; then
        echo -e "Date: $DATE
Host: $IP
Total: $TOTAL
Problem: $PART=$USE% ($MOUNT)" | mail -s "Disk Monitor" $MAIL
    fi
done

8. Remote Disk Usage Monitoring

#!/bin/bash
HOST_INFO=host.info
for IP in $(awk '/^[^#]/{print $1}' $HOST_INFO); do
    USER=$(awk -v ip=$IP '$1==ip{print $2}' $HOST_INFO)
    PORT=$(awk -v ip=$IP '$1==ip{print $3}' $HOST_INFO)
    TMP_FILE=/tmp/disk.tmp
    ssh -p $PORT $USER@$IP "df -h" > $TMP_FILE
    USE_RATE_LIST=$(awk 'BEGIN{OFS="="}/^\/dev/{print $1,int($5)}' $TMP_FILE)
    for USE_RATE in $USE_RATE_LIST; do
        PART_NAME=${USE_RATE%=*}
        RATE=${USE_RATE#*=}
        if [ $RATE -ge 80 ]; then
            echo "Warning: $PART_NAME Partition usage $RATE%!"
        fi
    done
done

9. Website Availability Check

Single Check

check_url() {
    HTTP_CODE=$(curl -o /dev/null --connect-timeout 3 -s -w "%{http_code}" $1)
    if [ $HTTP_CODE -ne 200 ]; then
        echo "Warning: $1 Access failure!"
    fi
}
# Usage: check_url www.baidu.com

Three‑Attempt Check

#!/bin/bash
check_url() {
    HTTP_CODE=$(curl -o /dev/null --connect-timeout 3 -s -w "%{http_code}" $1)
    if [ $HTTP_CODE -eq 200 ]; then
        return 0
    else
        return 1
    fi
}
URL_LIST="www.baidu.com www.agasgf.com"
for URL in $URL_LIST; do
    FAIL_COUNT=0
    for i in {1..3}; do
        if check_url $URL; then
            break
        else
            let FAIL_COUNT++
        fi
    done
    if [ $FAIL_COUNT -eq 3 ]; then
        echo "Warning: $URL Access failure!"
    fi
done

10. MySQL Master‑Slave Synchronization Status

#!/bin/bash
USER=bak
PASSWD=123456
IO_SQL_STATUS=$(mysql -u$USER -p$PASSWD -e "show slave status" | awk -F: '/Slave_.*_Running/{gsub(": ",":");print $0}')
for i in $IO_SQL_STATUS; do
    THREAD_STATUS_NAME=${i%:*}
    THREAD_STATUS=${i#*:}
    if [ "$THREAD_STATUS" != "Yes" ]; then
        echo "Error: MySQL Master‑Slave $THREAD_STATUS_NAME status is $THREAD_STATUS!"
    fi
done

These scripts are intended as practical examples for interview preparation and daily operations; copying without understanding will not lead to mastery.