How to Monitor Recently Modified Files in Last 24 Hours on Linux

How to Monitor Recently Modified Files in Last 24 Hours on Linux

Need to investigate what changed on your server today? Looking to catch unauthorized modifications that happened in the past day? This guide shows you how to quickly identify files modified within the last 24 hours—perfect for security incident response, daily audits, and detecting today's suspicious activity.

Why Focus on Last 24 Hours?

Monitoring files changed in the last 24 hours is crucial for several reasons:

Incident Response: When investigating a security breach or system issue, you need to know what changed recently. Files modified in the last day are often the smoking gun.

Daily Security Audits: Running a daily check of yesterday's file changes helps catch unauthorized modifications before they cause bigger problems. It's like checking your server's "recent activity" log.

Today's Activity Tracking: Unlike broader monitoring that shows weeks of changes, focusing on 24 hours gives you a clear picture of what happened today versus historical patterns.

Performance: Scanning only the last 24 hours is faster and produces fewer false positives than scanning weeks of history. You get actionable results without noise.

Compliance Requirements: Many security policies require daily audits of file modifications. A 24-hour window makes compliance reporting straightforward.

Quick Commands for 24-Hour File Changes

These commands specifically target files modified within the last 24 hours (since yesterday):

Files Modified in Last 24 Hours

# Files modified in last 24 hours
find / -mtime -1

# Files modified in last 24 hours with details
find / -mtime -1 -ls

# Files modified in last 24 hours excluding system directories
find / -mtime -1 -not -path "/proc/*" -not -path "/sys/*"

Files Modified in Last Hour

# Files modified in last hour
find / -mmin -60

# Files modified in last hour with timestamps
find / -mmin -60 -printf '%T+ %p\n' | sort -r

# Files modified in last hour with details
find / -mmin -60 -ls

Recently Modified Files with Details

# Recently modified files with details
find / -mtime -1 -ls

# Recently modified files with timestamps
find / -mtime -1 -printf '%T+ %p\n' | sort -r | head -20

# Recently modified files with size
find / -mtime -1 -printf '%T+ %s %p\n' | sort -r

Exclude System Directories

# Exclude system directories
find / -mtime -1 -not -path "/proc/*" -not -path "/sys/*" -not -path "/dev/*"

# Exclude multiple system directories
find / -mtime -1 -not -path "/proc/*" -not -path "/sys/*" -not -path "/dev/*" -not -path "/run/*"

# Exclude system directories with details
find / -mtime -1 -not -path "/proc/*" -not -path "/sys/*" -ls

Alternative Commands

# Recently modified files in specific directory
find /etc -mtime -1

# Recently modified files by extension
find / -mtime -1 -name "*.conf"

# Recently modified files sorted by modification time
find / -mtime -1 -printf '%T+ %p\n' | sort -r | head -20

Setting Up Daily 24-Hour Monitoring in Zuzia.app

Configure Zuzia.app to automatically check for files modified in the last 24 hours:

Step 1: Create Daily Check Task

1. Add New Scheduled Task

   • Go to Zuzia.app dashboard
   • Click "Add Scheduled Task"
   • Select "Command" as task type

2. Configure the 24-Hour Check Command

   • Command: find / -mtime -1 -not -path "/proc/*" -not -path "/sys/*" -not -path "/dev/*" -printf '%T+ %p\n' | sort -r
   • Schedule: Run daily (e.g., every morning at 8 AM)
   • Name it: "Daily 24-hour file change check"

Step 2: Set Up Smart Alerts

1. Critical File Alerts

   • Alert if files in /etc are modified (configuration changes)
   • Alert if files in /usr/bin or /usr/sbin are modified (system binaries)
   • Alert if unexpected files appear in root directories

2. Notification Setup

   • Email alerts for critical directory changes
   • Webhook alerts for integration with security tools
   • SMS for urgent security incidents (if configured)

Step 3: Daily Review Process

1. Morning Review Routine

   • Check dashboard each morning for yesterday's changes
   • Review the list of modified files
   • Flag any unexpected modifications for investigation

2. Incident Response Workflow

   • When investigating an incident, check the 24-hour report
   • Compare with baseline to identify anomalies
   • Use timestamps to correlate with other security events

Real-World Scenarios: When 24-Hour Monitoring Matters

Here are specific situations where checking the last 24 hours is essential:

Security Incident Investigation

The Scenario: You receive an alert that your server was compromised. You need to know what the attacker changed.

The Solution: Run the 24-hour check immediately. Files modified in the last day show you exactly what the attacker touched—modified config files, new backdoors, or altered system binaries. This narrow window makes incident response faster and more focused.

Daily Security Audits

The Scenario: Your compliance policy requires daily audits of file modifications.

The Solution: Schedule a daily 24-hour check every morning. Review yesterday's changes before starting your day. This creates a routine that catches unauthorized modifications quickly, often before they cause damage.

Detecting Today's Suspicious Activity

The Scenario: You notice unusual server behavior but aren't sure if it's a security issue or a misconfiguration.

The Solution: Check what changed today. If you see unexpected modifications to system files, configuration files, or application directories, you've found a potential security issue. The 24-hour window filters out legitimate historical changes.

Post-Update Verification

The Scenario: You applied system updates yesterday and want to verify what files were actually changed.

The Solution: The 24-hour check shows you exactly which files the update process modified. Compare this with expected update changes to ensure nothing unexpected happened.

Troubleshooting Application Issues

The Scenario: Your application started behaving strangely today, and you suspect a configuration file was changed.

The Solution: Check files modified in the last 24 hours, focusing on your application's configuration directory. This narrows down the investigation to recent changes rather than scanning weeks of history.

Optimizing Your 24-Hour File Checks

Make your daily checks more effective with these optimizations:

Focus on Critical Directories Only

Instead of scanning the entire filesystem, target high-value directories:

# Check only /etc (configuration files)
find /etc -mtime -1 -printf '%T+ %p\n' | sort -r

# Check only system binaries
find /usr/bin /usr/sbin -mtime -1 -printf '%T+ %p\n' | sort -r

# Check only web application files
find /var/www -mtime -1 -printf '%T+ %p\n' | sort -r

This reduces scan time and focuses alerts on the most important changes.

Exclude Temporary and System Directories

Skip directories that change constantly and aren't security-relevant:

find / -mtime -1 -not -path "/proc/*" -not -path "/sys/*" -not -path "/dev/*" -not -path "/run/*" -not -path "/tmp/*"

This eliminates noise from system directories that change constantly.

Compare with Baseline

Create a baseline of expected daily changes (log files, temporary files, etc.) and compare each day's results. This helps identify anomalies—if you normally see 50 files changed daily and suddenly see 200, something unusual happened.

Integrate with Log Analysis

Correlate file changes with system logs. If a file was modified at 2 AM, check what processes were running at that time. This helps determine if changes were authorized or suspicious.

What to Do When You Find Unexpected Changes

When your 24-hour check reveals suspicious modifications:

Immediate Investigation Steps

1. Check File Timestamps

   • Note exactly when files were modified (the %T+ format shows precise timestamps)
   • Correlate with system logs from that time
   • Check if any scheduled tasks or updates ran at that time

2. Verify File Contents

   • Compare modified files with backups or known-good versions
   • Look for suspicious content (backdoors, unexpected code, configuration changes)
   • Check file permissions—were they changed too?

3. Identify the Source

   • Check process logs to see what modified the files
   • Review user activity logs
   • Check if any automated processes ran at that time

Response Actions

1. If Unauthorized Changes Detected

   • Immediately isolate the affected system if possible
   • Restore files from known-good backups
   • Preserve evidence (copy modified files before restoring)
   • Investigate how the unauthorized access occurred

2. Prevent Future Incidents

   • Tighten file permissions on critical directories
   • Implement stricter access controls
   • Set up more frequent monitoring (every 12 hours instead of 24)
   • Enable file integrity monitoring for critical files

Best Practices for 24-Hour File Monitoring

Make your daily checks effective:

• Run at consistent times: Check every morning at the same time to establish a routine
• Focus on critical paths: Monitor /etc, /usr/bin, /usr/sbin, and application directories
• Document expected changes: Keep notes on what files normally change daily (logs, temp files)
• Set up alerts for anomalies: Alert when unexpected directories show changes
• Review before taking action: Don't panic—verify changes are actually suspicious
• Keep backups: Always have recent backups to compare against
• Correlate with other logs: Combine file checks with process logs and access logs

FAQ: Common Questions About Recently Modified File Monitoring

How often should I run the 24-hour check?

For most servers, running once per day (every 24 hours) is sufficient. Schedule it in the morning to review yesterday's changes. For high-security systems or during active incidents, you might run it every 12 hours. More frequent checks provide better security but increase system load and alert fatigue.

Should I scan the entire filesystem or specific directories?

For daily checks, focus on critical directories rather than scanning everything. Use find /etc -mtime -1 for configuration files, find /usr/bin /usr/sbin -mtime -1 for system binaries, or find /var/www -mtime -1 for web applications. This is faster, produces fewer false positives, and focuses on security-critical changes. Full filesystem scans are better for weekly or monthly audits.

What should I do if I see unexpected changes in critical directories?

First, don't panic. Check the timestamps—was a system update scheduled at that time? Verify the file contents against backups. If the changes are unauthorized, immediately check system logs from that time period, isolate the affected system if possible, and restore files from backups. Document everything for security investigation.

Can I exclude certain directories?

Yes, you can modify the find command to exclude directories. For example: find / -mtime -1 -not -path "/proc/*" -not -path "/sys/*" -not -path "/dev/*". Exclude system directories like /proc, /sys, /dev, /run to focus on actual files and improve performance. Excluding temporary directories reduces alert noise.

How do I detect unauthorized file changes?

Detect unauthorized file changes by comparing current file lists with baseline lists, monitoring for unexpected changes, checking file timestamps, reviewing file contents, and using automated comparison tools. Regular comparison helps identify unauthorized changes quickly. Use file integrity monitoring tools for comprehensive detection.

Can I track file changes over time?

Yes, Zuzia.app stores historical data, allowing you to track file changes over time. Review historical data to identify change patterns, compare current vs. historical files, detect unauthorized changes, and maintain audit trails. Historical data helps understand file change patterns and detect issues.

How does AI help with file monitoring?

If you have Zuzia.app's full package, AI analysis can detect file change patterns automatically, identify unusual file modifications, predict potential security risks, suggest security improvements, and provide insights for improving file security. AI helps you understand file change patterns and prevent security issues proactively.

What if I have many file changes?

If you have many file changes, filter monitoring to critical directories, exclude temporary files, use file type filters, set up intelligent alerts, and review changes regularly. Managing many changes requires good filtering and alert configuration to focus on important changes.

How do I prevent unauthorized file changes?

Prevent unauthorized file changes by implementing file integrity monitoring, restricting file access, monitoring file changes continuously, enforcing access control policies, reviewing file permissions regularly, and using automated monitoring. Multiple layers of security help prevent unauthorized changes.

Can I export file change data?

Yes, Zuzia.app allows you to export monitoring data. Export data for analysis, reporting, compliance, or security investigation. Use exported data to analyze file change patterns, create security reports, and investigate security incidents.