Configure Linux cron jobs and system task scheduling with best practices

#!/usr/bin/env bash

set -euo pipefail

# Colors for output
RED='\033[0;31m'
GREEN='\033[0;32m'
YELLOW='\033[1;33m'
BLUE='\033[0;34m'
NC='\033[0m' # No Color

# Global variables
SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
BACKUP_DIR="/tmp/cron-install-backup-$(date +%Y%m%d-%H%M%S)"
PKG_MGR=""
PKG_INSTALL=""
CRON_SERVICE=""
EMAIL_ADDRESS=""

# Error handling
trap 'error_exit "Installation failed at line $LINENO"' ERR

error_exit() {
    echo -e "${RED}ERROR: $1${NC}" >&2
    cleanup
    exit 1
}

cleanup() {
    echo -e "${YELLOW}Cleaning up temporary files...${NC}"
    # Restore backups if they exist
    if [ -d "$BACKUP_DIR" ]; then
        if [ -f "$BACKUP_DIR/crontab" ]; then
            crontab "$BACKUP_DIR/crontab" 2>/dev/null || true
        fi
    fi
}

usage() {
    echo "Usage: $0 [email@example.com]"
    echo "  email: Optional email address for cron notifications"
    exit 1
}

detect_distro() {
    echo -e "${BLUE}[1/8] Detecting distribution...${NC}"
    
    if [ ! -f /etc/os-release ]; then
        error_exit "Cannot detect distribution - /etc/os-release not found"
    fi
    
    . /etc/os-release
    case "$ID" in
        ubuntu|debian)
            PKG_MGR="apt"
            PKG_INSTALL="apt install -y"
            CRON_SERVICE="cron"
            ;;
        almalinux|rocky|centos|rhel|ol)
            PKG_MGR="dnf"
            PKG_INSTALL="dnf install -y"
            CRON_SERVICE="crond"
            ;;
        fedora)
            PKG_MGR="dnf"
            PKG_INSTALL="dnf install -y"
            CRON_SERVICE="crond"
            ;;
        amzn)
            PKG_MGR="yum"
            PKG_INSTALL="yum install -y"
            CRON_SERVICE="crond"
            ;;
        *)
            error_exit "Unsupported distribution: $ID"
            ;;
    esac
    
    echo -e "${GREEN}Detected: $PRETTY_NAME (using $PKG_MGR)${NC}"
}

check_prerequisites() {
    echo -e "${BLUE}[2/8] Checking prerequisites...${NC}"
    
    if [ "$EUID" -ne 0 ]; then
        error_exit "This script must be run as root or with sudo"
    fi
    
    # Create backup directory
    mkdir -p "$BACKUP_DIR"
    
    # Backup existing crontab if it exists
    if crontab -l >/dev/null 2>&1; then
        crontab -l > "$BACKUP_DIR/crontab"
        echo -e "${GREEN}Backed up existing crontab${NC}"
    fi
}

install_cron() {
    echo -e "${BLUE}[3/8] Installing and configuring cron service...${NC}"
    
    # Update package cache
    if [ "$PKG_MGR" = "apt" ]; then
        apt update
        $PKG_INSTALL cron rsync mailutils
    else
        $PKG_INSTALL cronie rsync mailx
    fi
    
    # Enable and start cron service
    systemctl enable --now "$CRON_SERVICE"
    
    if systemctl is-active --quiet "$CRON_SERVICE"; then
        echo -e "${GREEN}Cron service is running${NC}"
    else
        error_exit "Failed to start cron service"
    fi
}

setup_logging() {
    echo -e "${BLUE}[4/8] Setting up cron logging...${NC}"
    
    # Create log directory
    mkdir -p /var/log/cron-jobs
    chmod 755 /var/log/cron-jobs
    
    # Configure rsyslog for cron logging (if available)
    if systemctl is-active --quiet rsyslog 2>/dev/null; then
        if [ "$PKG_MGR" = "apt" ]; then
            # Enable cron logging in rsyslog
            if ! grep -q "cron" /etc/rsyslog.conf; then
                echo "cron.*    /var/log/cron.log" >> /etc/rsyslog.conf
                systemctl restart rsyslog
            fi
        fi
    fi
}

create_system_scripts() {
    echo -e "${BLUE}[5/8] Creating system maintenance scripts...${NC}"
    
    # Create daily cleanup script
    cat > /etc/cron.daily/system-cleanup << 'EOF'
#!/bin/bash
# Daily system cleanup script

# Clean package cache
if command -v apt-get >/dev/null 2>&1; then
    apt-get clean
    apt-get autoremove -y
elif command -v dnf >/dev/null 2>&1; then
    dnf clean packages
elif command -v yum >/dev/null 2>&1; then
    yum clean packages
fi

# Clean temporary files older than 7 days
find /tmp -type f -atime +7 -delete 2>/dev/null || true

# Clean journal logs older than 30 days
if command -v journalctl >/dev/null 2>&1; then
    journalctl --vacuum-time=30d
fi

# Update locate database if available
if command -v updatedb >/dev/null 2>&1; then
    updatedb
fi

echo "$(date): System cleanup completed" >> /var/log/cron-jobs/cleanup.log
EOF

    chmod 755 /etc/cron.daily/system-cleanup
    
    # Create weekly log rotation script
    cat > /etc/cron.weekly/log-rotation << 'EOF'
#!/bin/bash
# Weekly log rotation for custom cron logs

# Rotate cron job logs
if [ -f /var/log/cron-jobs/backup.log ]; then
    mv /var/log/cron-jobs/backup.log /var/log/cron-jobs/backup.log.old
    gzip /var/log/cron-jobs/backup.log.old 2>/dev/null || true
fi

if [ -f /var/log/cron-jobs/cleanup.log ]; then
    mv /var/log/cron-jobs/cleanup.log /var/log/cron-jobs/cleanup.log.old  
    gzip /var/log/cron-jobs/cleanup.log.old 2>/dev/null || true
fi

echo "$(date): Log rotation completed" >> /var/log/cron-jobs/rotation.log
EOF

    chmod 755 /etc/cron.weekly/log-rotation
}

setup_system_crontab() {
    echo -e "${BLUE}[6/8] Setting up system-wide cron jobs...${NC}"
    
    cat > /etc/cron.d/system-maintenance << EOF
# System maintenance cron jobs
SHELL=/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
MAILTO=root

# Update package database daily at 5 AM
0 5 * * * root /usr/bin/logger "Starting package database update" && ([ -x /usr/bin/apt ] && /usr/bin/apt update || [ -x /usr/bin/dnf ] && /usr/bin/dnf check-update || [ -x /usr/bin/yum ] && /usr/bin/yum check-update) >> /var/log/cron-jobs/package-update.log 2>&1

# Check disk usage daily at 6 AM
0 6 * * * root /bin/df -h >> /var/log/cron-jobs/disk-usage.log 2>&1

# Clean old compressed logs monthly
0 2 1 * * root /usr/bin/find /var/log -name "*.gz" -mtime +90 -delete 2>/dev/null
EOF

    chmod 644 /etc/cron.d/system-maintenance
}

setup_user_crontab() {
    echo -e "${BLUE}[7/8] Setting up example user cron jobs...${NC}"
    
    # Create a sample user crontab with proper environment
    cat > /tmp/user-crontab << EOF
# Environment variables for cron jobs
SHELL=/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOME=$HOME
EOF

    if [ -n "$EMAIL_ADDRESS" ]; then
        echo "MAILTO=$EMAIL_ADDRESS" >> /tmp/user-crontab
    fi

    cat >> /tmp/user-crontab << 'EOF'

# Example cron jobs (commented out by default)
# Backup home directory daily at 2 AM
# 0 2 * * * /usr/bin/rsync -av $HOME/Documents/ /backup/documents/ >> /var/log/cron-jobs/backup.log 2>&1

# Check system updates every Sunday at 1 AM  
# 0 1 * * 0 /usr/bin/logger "Checking for system updates" && (/usr/bin/apt list --upgradable 2>/dev/null || /usr/bin/dnf list updates 2>/dev/null || /usr/bin/yum list updates 2>/dev/null) >> /var/log/cron-jobs/updates.log 2>&1

# Monitor disk usage every 30 minutes during business hours
# */30 9-17 * * 1-5 /bin/df -h | /usr/bin/logger "Disk usage check"
EOF

    # Install the crontab for root (since we're running as root)
    crontab /tmp/user-crontab
    rm /tmp/user-crontab
}

verify_installation() {
    echo -e "${BLUE}[8/8] Verifying installation...${NC}"
    
    # Check cron service status
    if ! systemctl is-active --quiet "$CRON_SERVICE"; then
        error_exit "Cron service is not running"
    fi
    
    # Check if crontab was installed
    if ! crontab -l >/dev/null 2>&1; then
        error_exit "Crontab installation failed"
    fi
    
    # Check system cron file
    if [ ! -f /etc/cron.d/system-maintenance ]; then
        error_exit "System cron file was not created"
    fi
    
    # Check daily script
    if [ ! -x /etc/cron.daily/system-cleanup ]; then
        error_exit "Daily cleanup script is not executable"
    fi
    
    echo -e "${GREEN}✓ Cron service is running${NC}"
    echo -e "${GREEN}✓ User crontab configured${NC}"
    echo -e "${GREEN}✓ System cron jobs configured${NC}"
    echo -e "${GREEN}✓ Maintenance scripts created${NC}"
    echo -e "${GREEN}✓ Log directory created: /var/log/cron-jobs${NC}"
    
    echo -e "\n${GREEN}Cron installation completed successfully!${NC}"
    echo -e "\nUseful commands:"
    echo -e "  View user crontab: ${BLUE}crontab -l${NC}"
    echo -e "  Edit user crontab: ${BLUE}crontab -e${NC}"
    echo -e "  Check cron logs: ${BLUE}tail -f /var/log/cron${NC}"
    echo -e "  View custom logs: ${BLUE}ls -la /var/log/cron-jobs/${NC}"
    
    if [ -n "$EMAIL_ADDRESS" ]; then
        echo -e "  Email notifications configured for: ${BLUE}$EMAIL_ADDRESS${NC}"
    fi
}

main() {
    # Parse arguments
    if [ $# -gt 1 ]; then
        usage
    fi
    
    if [ $# -eq 1 ]; then
        if [[ $1 =~ ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ ]]; then
            EMAIL_ADDRESS="$1"
        else
            error_exit "Invalid email address format"
        fi
    fi
    
    echo -e "${GREEN}Starting cron installation and configuration...${NC}"
    
    detect_distro
    check_prerequisites
    install_cron
    setup_logging
    create_system_scripts
    setup_system_crontab
    setup_user_crontab
    verify_installation
    
    # Cleanup backup directory on success
    rm -rf "$BACKUP_DIR"
    
    echo -e "${GREEN}Installation complete!${NC}"
}

main "$@"