Linux Server Init & SSH Hardening Script

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A production-ready, POSIX-compliant shell script designed to initialize Linux servers and harden SSH security in minutes.

It safely handles SSH key deployment, port changing, user creation, TCP BBR enablement, and system updates, while ensuring compatibility across Debian, Ubuntu, CentOS, RHEL, and Alpine Linux.

✨ Key Features

• Universal Compatibility: Works flawlessly on Debian, Ubuntu, CentOS/RHEL, Alma/Rocky, and Alpine Linux.
• POSIX Compliant: Written in pure /bin/sh. No bash dependency. Runs perfectly on dash (Debian) and ash (Alpine/Busybox).
• Security Architecture (Fortress Pro):
  • Managed Config Block: Inserts configuration at the top of sshd_config to strictly override vendor defaults (bypasses the Debian 12 Include trap).
  • Auto-Rollback: If SSHD validation fails, port is not listening, or connection test fails during execution, the script automatically reverts all system changes.
  • Service Protection (Anti-Kill): Adds a systemd override.conf to prevent OOM kills and ensures SSHD restarts automatically on failure.
  • Deadlock Prevention: Intelligently detects authentication states to prevent "Password Disabled + No Key" lockouts.
• Automation Friendly:
  • Supports Headless Mode allowing zero-interaction unattended installation.
  • Audit & Reporting: Automatically generates detailed operation audit logs and system health reports.

🚀 Quick Start

Run the following command as root.

1. Interactive Run (Recommended)

curl -fsSL https://raw.githubusercontent.com/247like/linux-ssh-init-sh/main/init.sh -o init.sh && chmod +x init.sh && ./init.sh

2. Force English UI

./init.sh --lang=en

🤖 Automation (Headless Mode)

Suitable for CI/CD pipelines or bulk provisioning. Use command line arguments to pass configurations and --yes to skip confirmation.

Full Automatic Example

(Configure Root user, random port, fetch key from GitHub, enable BBR, update system, auto-confirm)

curl -fsSL https://raw.githubusercontent.com/247like/linux-ssh-init-sh/main/init.sh | sh -s -- \
    --user=root \
    --port=random \
    --key-gh=247like \
    --bbr \
    --update \
    --yes

Semi-Automatic Example

(Specify key URL, choose other options manually)

./init.sh --key-url=https://my-server.com/id_ed25519.pub

⚙️ Arguments

The script supports rich command-line arguments to control its behavior:

Category	Argument	Description
Control	--lang=en	Force English UI
	--yes	Auto Confirm: Skip the final "Proceed?" prompt
	--strict	Strict Mode: Exit immediately on error (see below)
	--delay-restart	Delay Restart: Apply config but do not restart SSHD immediately
User/Port	--user=root	Specify login user (root or username)
	--port=22	Keep default port 22
	--port=random	Generate random high port (49152-65535)
	--port=2222	Specify a specific port number
Keys	--key-gh=username	Fetch public key from GitHub
	--key-url=url	Download public key from URL
	--key-raw="ssh-..."	Pass public key string directly
System	--update	Enable system package update
	--no-update	Skip system update
	--bbr	Enable TCP BBR congestion control
	--no-bbr	Disable BBR

⚙️ Normal Mode vs. Strict Mode

Feature	Normal Mode (Default)	Strict Mode (--strict)
Philosophy	"Don't Lockout" (Best Effort)	"Compliance First" (Zero Tolerance)
Key Failure	If key download fails, script keeps Password Auth enabled and warns you. 👉 Result: Server reachable but less secure.	Script exits immediately. No changes applied. 👉 Result: Deployment aborted, state unchanged.
Port Failure	If random port fails, it falls back to Port 22.	Script exits immediately.

📂 Logs & Audit

After execution, the following files are generated for troubleshooting and auditing:

• Run Log: /var/log/server-init.log (Detailed debug information)
• Audit Log: /var/log/server-init-audit.log (Records key actions, timestamps, and operators)
• Health Report: /var/log/server-init-health.log (Snapshot of the final system configuration state)

🆘 Disaster Recovery & Restore

The script features a dual-layer safety mechanism: Runtime Auto-Rollback and Persistent Backup Restore.

If you cannot connect to your server via SSH after the script finishes (after seeing "DONE"), log in via your Cloud Provider's VNC / Console and use one of the following methods.

Method A: One-Click Restore Script (Recommended)

The script automatically creates a backup and generates a restore script before applying changes.

1. Find the latest backup directory:

   ls -ld /var/backups/ssh-config/*
   

2. Enter the directory and run the restore script:

   # Enter the latest timestamp directory (e.g., 20250520_120000)
   cd /var/backups/ssh-config/<TIMESTAMP>/
   
   # Run the restore script
   sh restore.sh
   

   This will automatically overwrite sshd_config and attempt to restart the SSH service.

Method B: Manual Restore

If the restore script is unavailable, manually copy the files:

# 1. Overwrite configuration
cp /var/backups/ssh-config/<TIMESTAMP>/sshd_config /etc/ssh/sshd_config

# 2. Restart Service
systemctl restart sshd || service sshd restart

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⚠️ Disclaimer

This script modifies critical system configurations (SSH). While it includes multiple safety checks and automatic rollback mechanisms, please ensure you have an alternative access method (such as a VNC/KVM Console) to your server to prevent lockout in case of network interruptions or unexpected configuration errors.

📄 License

This project is released under the MIT License.

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