Ubuntu

How to: Install a swap file in a Windows Azure Ubuntu VM 2.0

by Juan Carlos · May 12, 2018

How to: Install a swap file in a Windows Azure Ubuntu VM

Unless you made your own Ubuntu image, configured the Azure connector/integration to create a swap file and uploaded it to Windows Azure chances are your VM does not come with a swap file/memory. Afterall Microsoft recommends that all Linux machines that are uploaded to the cloud come without a swap file to avoid issues. The application you install to configure your VM (think of sysprep for Linux) has a parameter to allow a swap file to be automatically created when you deploy the VM. The nice thing about it, is that now you can modify the configuration file and upon the restart of the service or reboot of the computer it will take care of creating the swap file for you! Isn’t that amazing!

BTW, I recommend reading this article too: How to: Configure Swappiness in Ubuntu. This is very important if you care about the performance of your VM after you have enabled swap memory.

So let’s get started!

Notes

The following information was obtained from the Microsoft website.
The following commands are executed as root.
You should set the swap file in compliance with the guidance from your Linux vendor:
- Ubuntu
- Red Hat
Before you create a swap file, you can run the following command to learn how much space is available under /mnt/resource or /mnt:

df -h

Edit the /etc/waagent.conf file:
1. To create a swap file in the directory that’s defined by the ResourceDisk.MountPoint parameter, you can update the following three parameters:
```
ResourceDisk.Format=y
ResourceDisk.EnableSwap=y
ResourceDisk.SwapSizeMB=xx
```
  Note The xx placeholder represents the desired number of megabytes (MB) for the swap file. As mentioned above, execute df -h to see how much available space you have on /mnt or /mnt/resouces. I say this because for example the 4GB temp storage disk after formatting and what not turns out to be around 3.7 GB. In that case I used 3.5GB or 3584 above to be on the safe side.
Restart the WALinuxAgent service by running one of the following commands, depending on the system in question:

Ubuntu: service walinuxagent restart

Red Hat/Centos: service waagent restart
Run one of the following commands to show the new swap apace that’s being used after the restart:

dmesg | grep swap

swapon -s

cat /proc/swaps

file /mnt/resource/swapfile
free| grep -i swap
If the swap file isn’t created, you can restart the virtual machine by using one of the following commands:
shutdown -r now
init 6

Personally I would strongly suggest you make sure you don’t assign more MB to the swap file than there are available otherwise you will run into system issues to the point you might not be able to log in to the server any more. Careful when resizing your VMs as well, as the available disk space may go up or down. Turn of swap files before resizing your VM and turn them back on when done. Obviously if you swap is say 2 GB then your temporary hard drive would never be smaller than that so you’re always safe. Generally you don’t need to reboot to observer the swap file being created and properly used. If it doesn’t work with the service restart double/triple check everything and use a reboot as a last resource. Good luck!

How to: Install a swap file in a Windows Azure Ubuntu VM 2.0