How do I install the Sysadmin Security skill?

Run npx skillmds@latest add hermeticormus/sysadmin-security in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Sysadmin Security safe to use?

This skill has not completed SkillMD's automated safety review yet. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with Sysadmin Security?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Sysadmin Security free to use?

Yes. Installing skills from SkillMD is free. This skill is licensed under MIT.

Who published Sysadmin Security?

hermeticormus (@hermeticormus) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Sysadmin Security by hermeticormus — Agent Skill

Name: Sysadmin Security
Author: hermeticormus

Sysadmin Security

Security audit and hardening for Debian/Ubuntu Linux systems covering user access, SSH, firewall, ports, file permissions, updates, and backups. Explains each change's benefit and lock-out risk before applying. Use when auditing or hardening a server or workstation.

File contents

System security audit

Audit and improve the security of a Debian/Ubuntu Linux machine. Work through the checklist below interactively. Inspection is read-only and runs freely; every change is explained first, including how it could lock you out, and waits for confirmation.

Security checklist

1. User and access control

Review user accounts: who should have access?
Check for unused accounts.
Verify sudo permissions.
Review SSH keys.
Check password policies.
Disable root login over SSH.

2. SSH hardening

Disable password authentication in favor of keys.
Change the default SSH port (optional).
Configure fail2ban.
Limit SSH access by user or IP.
Use SSH key passphrases.
Review ~/.ssh/authorized_keys.

3. Firewall

Enable UFW (Uncomplicated Firewall).
Configure allowed ports.
Block unnecessary services.
Review current rules.
Set a default-deny policy.

4. Updates and patches

Check for system updates with apt update.
Enable automatic security updates.
Review update history.
Check for end-of-life software.

5. Services and ports

List running services with systemctl.
Disable unnecessary services.
Review open ports with ss -tlnp.
Check listening services.
Verify service permissions.

6. File permissions

Check sensitive file permissions (/etc/passwd, /etc/shadow).
Review home directory permissions.
Check SUID/SGID files.
Verify critical system files.

7. Logs and monitoring

Review system logs with journalctl.
Check authentication logs.
Monitor failed login attempts.
Set up log rotation.
Consider log monitoring tools.

8. Application security

Review installed packages with apt list --installed.
Remove unnecessary software.
Check for vulnerable packages.
Update applications.
Verify sources (PPAs, repositories).

9. Network security

Review network interfaces.
Check the routing table.
Verify DNS settings.
Review /etc/hosts.
Check for suspicious connections.

10. Backup and recovery

Verify backups exist.
Test backup restoration.
Document the recovery process.
Secure backup storage.

Running the checks

Guide me through running each check and implementing hardening measures. Explain each step and the security benefit.

Safety first: explain the risks before any change that could lock me out, especially SSH, firewall, and account changes.

See full content at https://github.com/HermeticOrmus/linux-sysadmin-skills.

---name: sysadmin-securitydescription: Security audit and hardening for Debian/Ubuntu Linux systems covering user access, SSH, firewall, ports, file permissions, updates, and backups. Explains each change's benefit and lock-out risk before applying. Use when auditing or hardening a server or workstation.license: MIT---# System security auditAudit and improve the security of a Debian/Ubuntu Linux machine. Work through the checklist below interactively. Inspection is read-only and runs freely; every change is explained first, including how it could lock you out, and waits for confirmation.## Security checklist### 1. User and access control- Review user accounts: who should have access?- Check for unused accounts.- Verify sudo permissions.- Review SSH keys.- Check password policies.- Disable root login over SSH.### 2. SSH hardening- Disable password authentication in favor of keys.- Change the default SSH port (optional).- Configure fail2ban.- Limit SSH access by user or IP.- Use SSH key passphrases.- Review `~/.ssh/authorized_keys`.### 3. Firewall- Enable UFW (Uncomplicated Firewall).- Configure allowed ports.- Block unnecessary services.- Review current rules.- Set a default-deny policy.### 4. Updates and patches- Check for system updates with `apt update`.- Enable automatic security updates.- Review update history.- Check for end-of-life software.### 5. Services and ports- List running services with `systemctl`.- Disable unnecessary services.- Review open ports with `ss -tlnp`.- Check listening services.- Verify service permissions.### 6. File permissions- Check sensitive file permissions (`/etc/passwd`, `/etc/shadow`).- Review home directory permissions.- Check SUID/SGID files.- Verify critical system files.### 7. Logs and monitoring- Review system logs with `journalctl`.- Check authentication logs.- Monitor failed login attempts.- Set up log rotation.- Consider log monitoring tools.### 8. Application security- Review installed packages with `apt list --installed`.- Remove unnecessary software.- Check for vulnerable packages.- Update applications.- Verify sources (PPAs, repositories).### 9. Network security- Review network interfaces.- Check the routing table.- Verify DNS settings.- Review `/etc/hosts`.- Check for suspicious connections.### 10. Backup and recovery- Verify backups exist.- Test backup restoration.- Document the recovery process.- Secure backup storage.## Running the checksGuide me through running each check and implementing hardening measures. Explain each step and the security benefit.**Safety first**: explain the risks before any change that could lock me out, especially SSH, firewall, and account changes.---See full content at https://github.com/HermeticOrmus/linux-sysadmin-skills.

Frequently asked questions