• Linux
• Systemd
• SwapEphemeralDrive

Linux/Systemd/SwapEphemeralDrive

• Create and enable swap file on Azure ephemeral drive

• shell script /root/azure-swapfile.sh

  # Azure Swap File Script
  # Version: 1.0
  # Created: 2025-11-13
  # Purpose: Automatically creates and activates swap file on Azure ephemeral disk (/mnt)
  
  # Hardcoded settings
  SWAP_SIZE="1G"
  SWAP_FILE="/mnt/swapfile"
  WAIT_SECS=30
  
  set -euo pipefail  # Exit on error, undefined vars, pipe failures
  
  # Function to cleanup on failure
  cleanup() {
    if [[ -f "$SWAP_FILE" ]] && ! swapon --show | grep -q "$SWAP_FILE"; then
      echo "Cleaning up incomplete swap file..."
      rm -f "$SWAP_FILE"
    fi
  }
  trap cleanup ERR
  
  # Wait for /mnt to be mounted
  echo "Waiting for /mnt to mount..."
  for ((i = 1; i <= WAIT_SECS; i++)); do
    if mountpoint -q /mnt; then
      echo "/mnt is mounted."
      break
    fi
    sleep 1
  done
  if ! mountpoint -q /mnt; then
    echo "Error: /mnt not mounted after ${WAIT_SECS}s. Exiting."
    exit 1
  fi
  
  # Convert size to bytes for comparison
  SWAP_SIZE_BYTES=$(numfmt --from=iec "$SWAP_SIZE")
  
  # Check if swap file exists and has correct size
  RECREATE_SWAP=false
  if [[ ! -f "$SWAP_FILE" ]]; then
    echo "Swap file does not exist."
    RECREATE_SWAP=true
  else
    CURRENT_SIZE=$(stat -f%z "$SWAP_FILE" 2>/dev/null || stat -c%s "$SWAP_FILE" 2>/dev/null)
    if [[ "$CURRENT_SIZE" != "$SWAP_SIZE_BYTES" ]]; then
      echo "Swap file size mismatch. Current: $CURRENT_SIZE bytes, Expected: $SWAP_SIZE_BYTES bytes."
      RECREATE_SWAP=true
    fi
  fi
  
  if [[ "$RECREATE_SWAP" == "true" ]]; then
    echo "Creating swap file: $SWAP_FILE ($SWAP_SIZE)"
    # Remove existing file if present
    [[ -f "$SWAP_FILE" ]] && rm -f "$SWAP_FILE"
  
    # Try fallocate first, fall back to dd if it fails
    if ! fallocate -l "$SWAP_SIZE" "$SWAP_FILE" 2>/dev/null; then
      echo "fallocate failed, using dd as fallback..."
      dd if=/dev/zero of="$SWAP_FILE" bs=1M count=$(numfmt --from=iec --to-unit=1048576 "$SWAP_SIZE") status=progress
    fi
  
    chmod 600 "$SWAP_FILE"
    mkswap "$SWAP_FILE"
    echo "Swap file created and formatted."
  else
    echo "Swap file exists with correct size; skipping creation."
  fi
  
  # Activate swap (idempotent: safe if already on)
  if ! swapon --show | grep -q "$SWAP_FILE"; then
    swapon "$SWAP_FILE"
    echo "Swap activated: $SWAP_FILE"
  else
    echo "Swap already active: $SWAP_FILE"
  fi
  
  # Display current swap status
  echo "Current swap status:"
  swapon --show

• systemd unit file /etc/systemd/system/azure-swapfile.service

  # Azure Swap File Service
  # Version: 1.0
  # Created: 2025-11-13
  # Purpose: Automatically creates and activates swap file on Azure ephemeral disk (/mnt)
  # Compatible with: Ubuntu/Debian on Azure VMs with ephemeral storage
  
  [Unit]
  Description=Activate Swap File on Azure Ephemeral Disk (/mnt)
  Documentation=https://learn.microsoft.com/en-us/azure/virtual-machines/linux/swap
  After=local-fs.target
  RequiresMountsFor=/mnt
  DefaultDependencies=yes
  
  [Service]
  Type=oneshot
  ExecStart=/root/azure-swapfile.sh
  RemainAfterExit=yes
  StandardOutput=journal
  StandardError=journal
  
  [Install]
  WantedBy=multi-user.target

• enable the systemd unit file

  sudo systemctl daemon-reload
  sudo systemctl enable azure-swapfile.service
  sudo systemctl start azure-swapfile.service
  
  sudo systemctl status azure-swapfile.service