Create a swap partition on ephemeral storage on Azure VM

by James McDonaldJun 13, 2025IT Tips0 comments

My VM has an 8G ephemeral volume and it seems to be wasted so why not put the swapfile on there

You need the cloud-init service:

sudo systemctl is-enabled cloud-init.service
enabled

The instructions with a couple of options are here: https://learn.microsoft.com/en-us/troubleshoot/azure/virtual-machines/linux/create-swap-file-linux-vm

Just in case the above link goes away:

Create a SWAP creation script named swap.sh under /var/lib/cloud/scripts/per-boot with the following script:

#!/bin/sh

# Percent of space on the ephemeral disk to dedicate to swap. Here 30% is being used. Modify as appropriate.
PCT=0.3

# Location of the swap file. Modify as appropriate based on the location of the ephemeral disk.
LOCATION=/mnt

if [ ! -f ${LOCATION}/swapfile ]
then

    # Get size of the ephemeral disk and multiply it by the percent of space to allocate
    size=$(/bin/df -m --output=target,avail | /usr/bin/awk -v percent="$PCT" -v pattern=${LOCATION} '$0 ~ pattern {SIZE=int($2*percent);print SIZE}')
    echo "$size MB of space allocated to swap file"

     # Create an empty file first and set correct permissions
    /bin/dd if=/dev/zero of=${LOCATION}/swapfile bs=1M count=$size
    /bin/chmod 0600 ${LOCATION}/swapfile

    # Make the file available to use as swap
    /sbin/mkswap ${LOCATION}/swapfile
fi

# Enable swap
/sbin/swapon ${LOCATION}/swapfile
/sbin/swapon -a

# Display current swap status
/sbin/swapon -s

The script will be executed on every boot and allocates 30% of the available space in the resource disk. You can customize the values based on your situation.

Make the script executable:

chmod +x /var/lib/cloud/scripts/per-boot/swap.sh

Stop and start the VM. Stopping and starting the VM is only necessary the first time after you create the SWAP file.

Create a swap partition on ephemeral storage on Azure VM

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