server-checkup

name	server-checkup
description	Systematic Linux server management. Use BEFORE making changes to capture baseline, then AFTER for verification. Triggers on 'check this server', 'audit', 'set up this machine', 'security audit', 'harden this Pi', 'fresh Pi setup', 'provision this server'. (user)
allowed-tools	["Bash","Read","Write","Edit","Glob","Grep"]

Server Maintenance

Systematic Linux server management with autonomous execution, risk assessment, and documentation.

When to Use

• Setting up a new server or Pi
• Security audit or hardening
• Health check on existing infrastructure
• Before and after major changes (baseline → verify)
• Post-reflash configuration

When NOT to Use

• Non-Linux systems (macOS, Windows)
• Cloud-managed services (use provider tools)
• Quick one-off commands (just run them)

Execution Modes

Interactive Mode (default)

Claude executes each phase, reports findings, asks for decisions on fixes.

Auto Mode (advanced)

Spawns subagents for each phase automatically. Faster but less control.

Trigger auto mode: "full server audit" or "audit thoroughly"

Partial Audits

• "security audit: " → Phases 0, 2 only
• "setup maintenance: " → Phases 0, 3 only
• "tailscale check: " → Phases 0, 4 only

Phase Workflow

Phase 0: Context Discovery (NEW)

Check for existing documentation FIRST:

1. Look for server-specific docs:

   ls -la | grep -iE '(server|setup|readme|hostname)\.md'
   ls -la .claude/CLAUDE.md 2>/dev/null
   

2. If found, read and extract:

   • Services that should be running
   • Expected configurations (ports, paths, versions)
   • Known issues/quirks
   • Previous maintenance history
   • Setup steps that reveal intent

3. Store context for validation:

   • Compare actual state vs documented state
   • Flag discrepancies as findings
   • Incorporate known good configs

Example: If docs say "reboot at 04:00" but config shows "02:00" → flag for review.

Phase 1: Connect & Triage

CRITICAL: Capture baseline FIRST (before any changes):

echo "=== BASELINE $(date +'%Y-%m-%d %H:%M') ===" | tee /tmp/server-baseline.txt
echo "Memory:" | tee -a /tmp/server-baseline.txt
free -h | tee -a /tmp/server-baseline.txt
echo -e "\nDisk:" | tee -a /tmp/server-baseline.txt
df -h / | tee -a /tmp/server-baseline.txt
echo -e "\nPackages:" | tee -a /tmp/server-baseline.txt
dpkg -l | grep -c '^ii' | tee -a /tmp/server-baseline.txt
echo -e "\nServices:" | tee -a /tmp/server-baseline.txt
systemctl list-units --type=service --state=running --no-pager | wc -l | tee -a /tmp/server-baseline.txt

System discovery:

1. Check for errors:

   # Without sudo (may fail, that's ok)
   dmesg 2>/dev/null | grep -iE 'error|fail|warn' | tail -20
   
   # With sudo if needed
   sudo dmesg | grep -iE 'error|fail|warn' | tail -20
   

2. Hardware & OS:

   uname -a && cat /etc/os-release | head -5
   free -h && df -h /
   dpkg -l | grep -c '^ii'  # package count
   

3. Initial assessment:

   • Note unusual errors
   • Check if disk space concerning (>80%)
   • Check if memory concerning (<500MB available)

Phase 2: Security Audit

SSH Configuration:

grep -E '^(Password|PermitRoot|X11)' /etc/ssh/sshd_config /etc/ssh/sshd_config.d/* 2>/dev/null | grep -v '^#'

Target state:

• PasswordAuthentication no ✅
• PermitRootLogin no ✅
• X11Forwarding no ✅ (headless servers)

Sudo configuration:

sudo ls -la /etc/sudoers.d/

Network exposure:

# Listening ports (external only)
ss -tlnp 2>/dev/null | grep -v '127.0.0' | grep -v tailscale

# Firewall status
sudo systemctl status ufw 2>&1 | head -5 || sudo iptables -L -n | head -10

Security scoring (auto-applied):

Finding	Risk Level	Fix Command
Password auth enabled	CRITICAL	echo "PasswordAuthentication no" | sudo tee -a /etc/ssh/sshd_config.d/99-hardening.conf && sudo systemctl reload sshd
Root login enabled	CRITICAL	echo "PermitRootLogin no" | sudo tee -a /etc/ssh/sshd_config.d/99-hardening.conf && sudo systemctl reload sshd
No firewall + port forwarding + external exposure	HIGH	Install ufw: sudo apt install ufw
No firewall + behind NAT + VPN only	LOW	Router + VPN provide protection
X11Forwarding on headless	MEDIUM	echo "X11Forwarding no" | sudo tee -a /etc/ssh/sshd_config.d/99-hardening.conf && sudo systemctl reload sshd

Phase 3: Maintenance Setup

Check unattended-upgrades:

dpkg -l unattended-upgrades 2>&1 | grep '^ii'

If missing: sudo apt install unattended-upgrades

Review configuration:

sudo grep -E '^(Unattended-Upgrade::(Allowed-Origins|Remove|Automatic-Reboot))' /etc/apt/apt.conf.d/50unattended-upgrades | head -20

Target configuration:

• All packages (not just security) - see references/unattended-upgrades.md
• Auto-reboot enabled with specific time
• Unused packages removed
• Custom repos included (Tailscale, Plex, etc.)

Verify service:

systemctl status unattended-upgrades --no-pager | head -8

Check reboot time is uncommented:

sudo grep "Automatic-Reboot-Time" /etc/apt/apt.conf.d/50unattended-upgrades

Phase 4: Tailscale (if applicable)

Check if Tailscale installed:

which tailscale && tailscale version || echo "Not installed"

If installed, check status:

tailscale status --self 2>&1 | head -3
tailscale status 2>&1 | grep -E 'exit node|subnet' | head -5

Verify IP forwarding persisted:

cat /etc/sysctl.d/99-tailscale.conf 2>/dev/null

Should contain:

net.ipv4.ip_forward = 1
net.ipv6.conf.all.forwarding = 1

Post-setup reminder: Disable key expiry in admin console for always-on nodes.

Phase 5: Cleanup

Identify unnecessary packages:

dpkg -l | grep -E '^ii.*(man-db|bluetooth|bluez|avahi|pulseaudio|alsa)' | awk '{print $2}' | sort

Check unnecessary services:

systemctl list-unit-files | grep enabled | grep -E '(bluetooth|avahi|serial-getty)'

Common removals for headless servers:

Package/Service	Why Remove	Risk	Command
man-db	Slows apt updates rebuilding man pages	LOW	sudo apt remove --purge -y man-db
avahi-daemon	mDNS not needed with Tailscale/static IPs	LOW	sudo systemctl disable --now avahi-daemon.service avahi-daemon.socket
bluetooth packages	Not used on servers	LOW	Keep libs, remove daemon if running
serial-getty	Not needed on headless	LOW	sudo systemctl disable serial-getty@ttyS0

Subagent decision matrix:

Scenario	Use Subagent?	Rationale
Remove 1-2 packages	❌	Use apt remove | tail -10
Remove 5+ packages	✅	Verbose output exhausts context
Check 1-2 services	❌	Direct commands fine
Full service audit	✅	Lots of parsing needed

Rule: If operation produces >200 lines, use subagent.

CRITICAL: Use terse output to avoid context exhaustion:

# Good - terse
sudo apt remove -y pkg1 pkg2 pkg3 2>&1 | tail -10

# Bad - verbose
sudo apt remove -y pkg1 pkg2 pkg3  # Full output

Phase 6: Verification

Compare against baseline:

echo -e "\n=== AFTER $(date +'%Y-%m-%d %H:%M') ===" | tee -a /tmp/server-baseline.txt
free -h | grep "Mem:" | tee -a /tmp/server-baseline.txt
df -h / | tail -1 | tee -a /tmp/server-baseline.txt
dpkg -l | grep -c '^ii' | tee -a /tmp/server-baseline.txt
systemctl list-units --type=service --state=running --no-pager | wc -l | tee -a /tmp/server-baseline.txt

Key services check:

systemctl list-units --type=service --state=running --no-pager | grep -E 'ssh|tailscale|docker|NetworkManager|unattended'

Final summary:

echo "=== Memory ===" && free -h | head -2
echo "=== Disk ===" && df -h /
echo "=== Packages ===" && dpkg -l | grep -c '^ii'

Show improvements:

• Memory freed
• Disk space saved
• Packages removed
• Services disabled

Phase 7: Report Generation (NEW)

Create maintenance record:

Option A: Append to existing server doc (if found in Phase 0)

## Maintenance History

### YYYY-MM-DD: <Brief Summary>

**Findings:**
- [Risk Level] Finding description
  - Fixed: command/action taken

**Changes Applied:**
- Security: X11 disabled, SSH hardened
- Cleanup: Removed N packages, disabled M services
- Performance: Freed XGB RAM, XGB disk

**System Health:**
- Memory: X available
- Disk: X% used
- Services: N running
- Uptime: N days

Option B: Create new maintenance report

Save as MAINTENANCE-YYYY-MM-DD.md:

# Server Maintenance: <hostname>
Date: YYYY-MM-DD
Auditor: Claude Code

## Executive Summary
- **Overall Risk:** Low/Medium/High
- **Findings:** N total (X critical, Y high, Z medium)
- **Time to Fix:** ~N minutes
- **Changes Applied:** N fixes

## Critical Issues
[Auto-populated from Phase 2 findings with CRITICAL/HIGH risk]

## Security Audit
- SSH: ✅/⚠️
- Firewall: ✅/⚠️
- Services: ✅/⚠️

## Maintenance Setup
- Unattended-upgrades: ✅/⚠️
- Auto-reboot: ✅/⚠️
- Custom repos: ✅/⚠️

## Changes Applied
[Commands run with output summary]

## System Health
**Before:**
- Memory: X available
- Disk: X% used
- Packages: N installed

**After:**
- Memory: X available (+Y freed)
- Disk: X% used (+Y freed)
- Packages: N installed (-Y removed)

## Services Inventory
[What's running and why - from Phase 0 context + discovery]

## Recommendations
[Remaining issues sorted by risk level with fix commands]

Ask user: "Should I append to existing .md or create new MAINTENANCE-.md?"

Decision Logic & Risk Scoring

Automatic Risk Assessment

Each finding is automatically scored:

Risk Dimensions:

1. Security Impact: Does this expose the system?
2. Blast Radius: Local vs network vs internet exposure?
3. Exploit Difficulty: Easy (remote) vs Hard (local only)?

Risk Levels:

Level	Criteria	Action Timeframe
CRITICAL	Remote exploit possible, privileged access	Fix immediately
HIGH	Exposure + missing security control	Fix today
MEDIUM	Unnecessary attack surface, limited exposure	Fix this week
LOW	Optimization, minimal risk	Optional cleanup

Example Decision Trees

Firewall Assessment:

IF no_firewall AND (port_forwarding OR dmz_host):
  IF tailscale_only_access:
    RISK = MEDIUM  # VPN provides some protection
  ELSE:
    RISK = HIGH    # Direct internet exposure
ELSE IF no_firewall AND behind_nat AND no_port_forwarding:
  RISK = LOW       # Router provides basic protection

Service Assessment:

IF service_running AND service_name IN unnecessary_list:
  IF service_listening_externally:
    RISK = MEDIUM  # Unnecessary exposure
  ELSE IF service_localhost_only:
    RISK = LOW     # Just resource waste

Context Management

Problem: apt output, service lists, and package queries exhaust context during routine operations.

Solutions:

1. Terse Output (always)

# Good
apt remove pkg 2>&1 | tail -10
dpkg -l | grep -c '^ii'

# Bad
apt remove pkg  # Full output
dpkg -l         # List all packages

2. Subagents (for verbose operations)

When to use:

• Removing 5+ packages
• Auditing all systemd services
• Scanning large log files
• Full security scans

Example:

Use Task tool with subagent_type=Explore for package removal when >5 packages

3. Baseline Capture (before changes)

Store initial state, compare after changes to prove improvement.

4. Single Command Batching

# Good - one command
sudo apt remove -y pkg1 pkg2 pkg3 pkg4 pkg5

# Bad - five commands
sudo apt remove -y pkg1
sudo apt remove -y pkg2
...

Quick Reference

Passwordless sudo

echo "<user> ALL=(ALL) NOPASSWD: ALL" | sudo tee /etc/sudoers.d/010_<user>-nopasswd
sudo chmod 440 /etc/sudoers.d/010_<user>-nopasswd

SSH hardening config

cat <<'EOF' | sudo tee /etc/ssh/sshd_config.d/99-hardening.conf
PasswordAuthentication no
PermitRootLogin no
X11Forwarding no
EOF
sudo sshd -t && sudo systemctl reload sshd

Find unattended-upgrades repo origin

# Check package policy
apt-cache policy <package> | grep -E 'origin|http'

# Check repo metadata
cat /var/lib/apt/lists/*_InRelease | grep -E '^Origin:|^Label:|^Codename:'

Disable unnecessary service

sudo systemctl disable --now <service-name>

References

Available in references/ directory:

• unattended-upgrades.md - Repo origin patterns for Debian, Tailscale, Plex, etc.
• packages-to-remove.md - Common unnecessary packages for headless servers
• ssh-hardening.md - SSH configuration patterns and key-only auth
• terminal-compat.md - Ghostty/terminfo fixes for SSH compatibility

Anti-Patterns

Anti-Pattern	Problem	Fix
Streaming full apt output	Context exhaustion	| tail -10 or subagent
Removing packages one-by-one	Slow, verbose	Single apt remove pkg1 pkg2 pkg3
Skipping baseline	Can't measure improvement	Always capture BEFORE changes
Forgetting reboot time	Immediate reboots during day	Verify uncommented + reasonable time
Checking config after changes	Can't compare	Baseline first, then changes
Not documenting changes	Future confusion	Always generate/update maintenance docs

Usage Examples

check this server: kube.lan (user: admin)     # Full audit
security audit: vps01 (user: root)            # Security only
full server audit: production-db              # Auto mode
check this server: kube.lan, skip tailscale   # Skip phase