Essential Shell Automation Scripts for System Administration

1. Check Disk Usage

This script checks the system's disk usage and sends an email alert when usage exceeds a defined threshold.

#!/bin/bash
THRESHOLD=80
EMAIL="[email protected]"

df -H | grep -vE '^Filesystem|tmpfs|cdrom' | awk '{ print $5 " " $1 }' | while read output; do
  usep=$(echo $output | awk '{ print $1}' | cut -d'%' -f1 )
  partition=$(echo $output | awk '{ print $2 }')
  if [ $usep -ge $THRESHOLD ]; then
    echo "Warning: The partition \"$partition\" has used $usep% at $(date)" | mail -s "Disk Space Alert: $partition" $EMAIL
  fi
done

2. Automatic MySQL Database Backup

This script creates daily backups of a MySQL database, stores them in a designated directory, and removes backups older than seven days.

#!/bin/bash
BACKUP_DIR="/backup/mysql"
MYSQL_USER="root"
MYSQL_PASSWORD="password"
DATABASE_NAME="mydatabase"

# Create backup directory
mkdir -p $BACKUP_DIR

# Create a new backup
mysqldump -u $MYSQL_USER -p$MYSQL_PASSWORD $DATABASE_NAME > $BACKUP_DIR/$DATABASE_NAME-$(date +%F).sql

# Remove backup files older than seven days
find $BACKUP_DIR -type f -mtime +7 -exec rm {} \;

3. Check and Restart Failed Service

This script verifies whether a specified service (e.g., nginx) is running; if it is down, the script attempts to restart it and sends notification emails about the status.

#!/bin/bash
SERVICE="nginx"
EMAIL="[email protected]"

if ! systemctl is-active --quiet $SERVICE; then
  echo "$SERVICE is down. Attempting to restart..." | mail -s "$SERVICE is down" $EMAIL
  systemctl restart $SERVICE
  if systemctl is-active --quiet $SERVICE; then
    echo "$SERVICE was successfully restarted" | mail -s "$SERVICE restarted" $EMAIL
  else
    echo "Failed to restart $SERVICE" | mail -s "$SERVICE restart failed" $EMAIL
  fi
fi

4. Clean Temporary Files

This script removes files in the /tmp directory that have not been modified for more than seven days and deletes empty sub‑directories.

#!/bin/bash
TEMP_DIR="/tmp"
DAYS=7

find $TEMP_DIR -type f -mtime +$DAYS -exec rm -f {} \;
find $TEMP_DIR -type d -empty -delete

5. System Resource Monitoring Script

This script records CPU and memory usage every minute and appends the information to a log file.

#!/bin/bash
LOG_FILE="/var/log/system_monitor.log"

while true; do
  echo "$(date): CPU: $(top -bn1 | grep \"Cpu(s)\" | awk '{print $2 + $4}')% MEM: $(free -m | awk 'NR==2{printf \"%.2f%%\", $3*100/$2 }')" >> $LOG_FILE
  sleep 60
done

6. Add User and Grant Sudo Privileges

This script creates a new user, sets an initial password, and adds the user to the sudo (wheel) group.

#!/bin/bash
# 自动添加用户并授予sudo权限脚本

if [ -z "$1" ]; then
    echo "Usage: $0 <username>"
    exit 1
fi

USERNAME=$1
PASSWORD="initial_password"  # 可以修改初始密码

# Check if user already exists
if id "$USERNAME" &>/dev/null; then
    echo "用户 $USERNAME 已存在。"
    exit 1
fi

# Add user
useradd -m $USERNAME
if [ $? -ne 0 ]; then
    echo "添加用户 $USERNAME 失败。"
    exit 1
fi

# Set user password
echo "$USERNAME:$PASSWORD" | chpasswd
if [ $? -ne 0 ]; then
    echo "设置用户 $USERNAME 的密码失败。"
    exit 1
fi

# Grant sudo privileges (wheel group for Ubuntu)
usermod -aG wheel $USERNAME
if [ $? -ne 0 ]; then
    echo "添加用户 $USERNAME 到 sudo 组失败。"
    exit 1
fi

echo "用户 $USERNAME 已添加并授予 sudo 权限。"

7. Scan Subnet for Active IPs

This script scans all IP addresses in a given /24 subnet, pings each address, and reports which hosts respond.

#!/bin/bash
# 网段IP扫描脚本

if [ -z "$1" ]; then
    echo "Usage: $0 <subnet>"
    echo "Example: $0 192.168.1"
    exit 1
fi

SUBNET=$1

echo "开始扫描网段 $SUBNET.0/24 ..."
for i in {1..254}; do
    IP="$SUBNET.$i"
    ping -c 1 -W 1 $IP &>/dev/null
    if [ $? -eq 0 ]; then
        echo "IP $IP 存活"
    fi
done

echo "扫描完成。"