This bash script setup a new user 'myuser' on your linux server and secure the SSH access.

vps-user-ssh-setup.sh

#!/bin/bash

# Variables
USERNAME="myuser"
SSH_PORT=22
EDIT_SSH_PORT=false
SSHD_CONFIG="/etc/ssh/sshd_config"
BACKUP_CONFIG="${SSHD_CONFIG}.bak_$(date +%Y%m%d%H%M%S)"

# Args parsing
while [[ "$#" -gt 0 ]]; do
  case "$1" in
    --username)
      USERNAME="$2"
      ;;
    --ssh-port)
      EDIT_SSH_PORT=true
      SSH_PORT="$2"
      shift
      ;;
    *)
      echo "Unknowned option : $1"
      echo "Usage : $0 [--username] [--ssh-port <port>]"
      exit 1
      ;;
  esac
  shift
done

# Check if user already exixts
if id "$USERNAME" &>/dev/null; then
  echo "ℹ️ User $USERNAME already exists."
else
  # Create new user and add it to sudo group
  adduser "$USERNAME"
  usermod -aG sudo "$USERNAME"
  echo "✅ The user $USERNAME has been created and added to sudo group."
fi

# Save SSHD file as backup in case something goes wrong
cp "$SSHD_CONFIG" "$BACKUP_CONFIG"
echo "📦 Backup of $SSHD_CONFIG done : $BACKUP_CONFIG"

# Secure SSH

# Disable root login
sed -i 's/^PermitRootLogin.*/PermitRootLogin no/' "$SSHD_CONFIG"

# Disable password authentication
sed -i 's/^#PasswordAuthentication yes/PasswordAuthentication no/' "$SSHD_CONFIG"
sed -i 's/^PasswordAuthentication yes/PasswordAuthentication no/' "$SSHD_CONFIG"
sed -i 's/^#UsePAM yes/UsePAM no/' "$SSHD_CONFIG"
sed -i 's/^UsePAM yes/UsePAM no/' "$SSHD_CONFIG"

# change SSH PORT if needed
if [ "$EDIT_SSH_PORT" = true ]; then
  sed -i -E 's/^#?Port[[:space:]]+[0-9]+/Port $SSH_PORT/' "$SSH_CONFIG"
fi

echo "Changing banner for ssh connexion"
tee /etc/issue.net > /dev/null <<'EOF'

⚠️ LEGAL NOTICE ⚠️

This system is for authorized use only.
Unauthorized access, use, or modification is strictly prohibited and may be subject to criminal prosecution.

All activities are logged and monitored.
By continuing, you acknowledge that you understand and accept these terms.

EOF
sed -i 's|^hashtag#Banner.*|Banner /etc/issue.net|' "$SSH_CONFIG"

# Check SSHD config before applying it
sshd -t
if [ $? -eq 0 ]; then
  # Restart SSH service
  systemctl restart sshd
  echo "🔐 Secure SSH access: root disabled, password disabled."
else
  echo "❌ Syntax error in $SSHD_CONFIG. Restoring backup."
  cp "$BACKUP_CONFIG" "$SSHD_CONFIG"
  systemctl restart sshd
fi