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Create and upload a CentOS-based Linux VHD in Azure	Learn to create and upload an Azure virtual hard disk (VHD) that contains a CentOS-based Linux operating system.	virtual-machines-linux		szarkos	timlt	tysonn	azure-resource-manager,azure-service-management	0e518e92-e981-43f4-b12c-9cba1064c4bb	virtual-machines-linux	infrastructure-services	vm-linux	na	article	05/09/2016	szark

Prepare a CentOS-based virtual machine for Azure

Prepare a CentOS 6.x virtual machine for Azure
Prepare a CentOS 7.0+ virtual machine for Azure

[!INCLUDE learn-about-deployment-models]

Prerequisites

This article assumes that you have already installed a CentOS (or similar derivative) Linux operating system to a virtual hard disk. Multiple tools exist to create .vhd files, for example a virtualization solution such as Hyper-V. For instructions, see Install the Hyper-V Role and Configure a Virtual Machine.

CentOS installation notes

Please see also General Linux Installation Notes for more tips on preparing Linux for Azure.
The VHDX format is not supported in Azure, only fixed VHD. You can convert the disk to VHD format using Hyper-V Manager or the convert-vhd cmdlet.
When installing the Linux system it is recommended that you use standard partitions rather than LVM (often the default for many installations). This will avoid LVM name conflicts with cloned VMs, particularly if an OS disk ever needs to be attached to another VM for troubleshooting. LVM or RAID may be used on data disks if preferred.
NUMA is not supported for larger VM sizes due to a bug in Linux kernel versions below 2.6.37. This issue primarily impacts distributions using the upstream Red Hat 2.6.32 kernel. Manual installation of the Azure Linux agent (waagent) will automatically disable NUMA in the GRUB configuration for the Linux kernel. More information about this can be found in the steps below.
Do not configure a swap partition on the OS disk. The Linux agent can be configured to create a swap file on the temporary resource disk. More information about this can be found in the steps below.
All of the VHDs must have sizes that are multiples of 1 MB.

CentOS 6.x

In Hyper-V Manager, select the virtual machine.
Click Connect to open a console window for the virtual machine.
Uninstall NetworkManager by running the following command:
```
 # sudo rpm -e --nodeps NetworkManager
```
Note: If the package is not already installed, this command will fail with an error message. This is expected.
Create a file named network in the /etc/sysconfig/ directory that contains the following text:
```
 NETWORKING=yes
 HOSTNAME=localhost.localdomain
```
Create a file named ifcfg-eth0 in the /etc/sysconfig/network-scripts/ directory that contains the following text:
```
 DEVICE=eth0
 ONBOOT=yes
 BOOTPROTO=dhcp
 TYPE=Ethernet
 USERCTL=no
 PEERDNS=yes
 IPV6INIT=no
```
Modify udev rules to avoid generating static rules for the Ethernet interface(s). These rules can cause problems when cloning a virtual machine in Microsoft Azure or Hyper-V:
```
 # sudo ln -s /dev/null /etc/udev/rules.d/75-persistent-net-generator.rules
 # sudo rm -f /etc/udev/rules.d/70-persistent-net.rules
```
Ensure the network service will start at boot time by running the following command:
```
 # sudo chkconfig network on
```
CentOS 6.3 Only: Install the drivers for the Linux Integration Services (LIS).

Important: The step is only valid for CentOS 6.3 and earlier. In CentOS 6.4+ the Linux Integration Services are already available in the standard kernel.
- Follow the installation instructions on the LIS download page and install the RPM onto your image.
Install the python-pyasn1 package by running the following command:
```
 # sudo yum install python-pyasn1
```

If you would like to use the OpenLogic mirrors that are hosted within the Azure datacenters, then replace the /etc/yum.repos.d/CentOS-Base.repo file with the following repositories. This will also add the [openlogic] repository that includes packages for the Azure Linux agent:

[openlogic]
name=CentOS-$releasever - openlogic packages for $basearch
baseurl=http://olcentgbl.trafficmanager.net/openlogic/$releasever/openlogic/$basearch/
enabled=1
gpgcheck=0

[base]
name=CentOS-$releasever - Base
baseurl=http://olcentgbl.trafficmanager.net/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

#released updates
[updates]
name=CentOS-$releasever - Updates
baseurl=http://olcentgbl.trafficmanager.net/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
baseurl=http://olcentgbl.trafficmanager.net/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
baseurl=http://olcentgbl.trafficmanager.net/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib
baseurl=http://olcentgbl.trafficmanager.net/centos/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

Note: The rest of this guide will assume you are using at least the [openlogic] repo, which will be used to install the Azure Linux agent below.

Add the following line to /etc/yum.conf:
```
http_caching=packages
```
And on CentOS 6.3 only add the following line:

exclude=kernel*
Disable the yum module "fastestmirror" by editing the file "/etc/yum/pluginconf.d/fastestmirror.conf", and under [main], type the following:
```
set enabled=0
```
Run the following command to clear the current yum metadata:
```
# yum clean all
```
On CentOS 6.3 only, update the kernel using the following command:
```
# sudo yum --disableexcludes=all install kernel
```
Modify the kernel boot line in your grub configuration to include additional kernel parameters for Azure. To do this, open "/boot/grub/menu.lst" in a text editor and ensure that the default kernel includes the following parameters:
```
console=ttyS0 earlyprintk=ttyS0 rootdelay=300 numa=off
```
This will also ensure all console messages are sent to the first serial port, which can assist Azure support with debugging issues. This will disable NUMA due to a bug in the kernel version used by CentOS 6.

In addition to the above, it is recommended to remove the following parameters:
```
rhgb quiet crashkernel=auto
```
Graphical and quiet boot are not useful in a cloud environment where we want all the logs to be sent to the serial port.

The crashkernel option may be left configured if desired, but note that this parameter will reduce the amount of available memory in the VM by 128MB or more, which may be problematic on the smaller VM sizes.
Ensure that the SSH server is installed and configured to start at boot time. This is usually the default.
Install the Azure Linux Agent by running the following command:
```
# sudo yum install WALinuxAgent
```
Note that installing the WALinuxAgent package will remove the NetworkManager and NetworkManager-gnome packages if they were not already removed as described in step 2.
Do not create swap space on the OS disk.

The Azure Linux Agent can automatically configure swap space using the local resource disk that is attached to the VM after provisioning on Azure. Note that the local resource disk is a temporary disk, and might be emptied when the VM is deprovisioned. After installing the Azure Linux Agent (see previous step), modify the following parameters in /etc/waagent.conf appropriately:
```
ResourceDisk.Format=y
ResourceDisk.Filesystem=ext4
ResourceDisk.MountPoint=/mnt/resource
ResourceDisk.EnableSwap=y
ResourceDisk.SwapSizeMB=2048    ## NOTE: set this to whatever you need it to be.
```
Run the following commands to deprovision the virtual machine and prepare it for provisioning on Azure:
```
# sudo waagent -force -deprovision
# export HISTSIZE=0
# logout
```
Click Action -> Shut Down in Hyper-V Manager. Your Linux VHD is now ready to be uploaded to Azure.

CentOS 7.0+

Changes in CentOS 7 (and similar derivatives)

Preparing a CentOS 7 virtual machine for Azure is very similar to CentOS 6, however there are several important differences worth noting:

The NetworkManager package no longer conflicts with the Azure Linux agent. This package is installed by default and we recommend that it is not removed.
GRUB2 is now used as the default bootloader, so the procedure for editing kernel parameters has changed (see below).
XFS is now the default file system. The ext4 file system can still be used if desired.

Configuration Steps

In Hyper-V Manager, select the virtual machine.
Click Connect to open a console window for the virtual machine.
Create a file named network in the /etc/sysconfig/ directory that contains the following text:
```
 NETWORKING=yes
 HOSTNAME=localhost.localdomain
```
Create a file named ifcfg-eth0 in the /etc/sysconfig/network-scripts/ directory that contains the following text:
```
 DEVICE=eth0
 ONBOOT=yes
 BOOTPROTO=dhcp
 TYPE=Ethernet
 USERCTL=no
 PEERDNS=yes
 IPV6INIT=no
```
Modify udev rules to avoid generating static rules for the Ethernet interface(s). These rules can cause problems when cloning a virtual machine in Microsoft Azure or Hyper-V:
```
 # sudo ln -s /dev/null /etc/udev/rules.d/75-persistent-net-generator.rules
```
Ensure the network service will start at boot time by running the following command:
```
 # sudo chkconfig network on
```
Install the python-pyasn1 package by running the following command:
```
 # sudo yum install python-pyasn1
```

If you would like to use the OpenLogic mirrors that are hosted within the Azure datacenters, then replace the /etc/yum.repos.d/CentOS-Base.repo file with the following repositories. This will also add the [openlogic] repository that includes packages for the Azure Linux agent:

 [openlogic]
 name=CentOS-$releasever - openlogic packages for $basearch
 baseurl=http://olcentgbl.trafficmanager.net/openlogic/$releasever/openlogic/$basearch/
 enabled=1
 gpgcheck=0

 [base]
 name=CentOS-$releasever - Base
 baseurl=http://olcentgbl.trafficmanager.net/centos/$releasever/os/$basearch/
 gpgcheck=1
 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

 #released updates
 [updates]
 name=CentOS-$releasever - Updates
 baseurl=http://olcentgbl.trafficmanager.net/centos/$releasever/updates/$basearch/
 gpgcheck=1
 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

 #additional packages that may be useful
 [extras]
 name=CentOS-$releasever - Extras
 baseurl=http://olcentgbl.trafficmanager.net/centos/$releasever/extras/$basearch/
 gpgcheck=1
 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

 #additional packages that extend functionality of existing packages
 [centosplus]
 name=CentOS-$releasever - Plus
 baseurl=http://olcentgbl.trafficmanager.net/centos/$releasever/centosplus/$basearch/
 gpgcheck=1
 enabled=0
 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

 #contrib - packages by Centos Users
 [contrib]
 name=CentOS-$releasever - Contrib
 baseurl=http://olcentgbl.trafficmanager.net/centos/$releasever/contrib/$basearch/
 gpgcheck=1
 enabled=0
 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

Note: The rest of this guide will assume you are using at least the [openlogic] repo, which will be used to install the Azure Linux agent below.

Run the following command to clear the current yum metadata and install any updates:
```
 # sudo yum clean all
 # sudo yum -y update
```
Modify the kernel boot line in your grub configuration to include additional kernel parameters for Azure. To do this, open "/etc/default/grub" in a text editor and edit the GRUB_CMDLINE_LINUX parameter, for example:
```
 GRUB_CMDLINE_LINUX="rootdelay=300 console=ttyS0 earlyprintk=ttyS0 net.ifnames=0"
```
This will also ensure all console messages are sent to the first serial port, which can assist Azure support with debugging issues. It also turns off the new CentOS 7 naming conventions for NICs. In addition to the above, it is recommended to remove the following parameters:
```
 rhgb quiet crashkernel=auto
```
Graphical and quiet boot are not useful in a cloud environment where we want all the logs to be sent to the serial port.

The crashkernel option may be left configured if desired, but note that this parameter will reduce the amount of available memory in the VM by 128MB or more, which may be problematic on the smaller VM sizes.
Once you are done editing "/etc/default/grub" per above, run the following command to rebuild the grub configuration:
```
 # sudo grub2-mkconfig -o /boot/grub2/grub.cfg
```
Ensure that the SSH server is installed and configured to start at boot time. This is usually the default.
Only if building the image from VMWare, VirtualBox or KVM: Add Hyper-V modules into initramfs:

Edit /etc/dracut.conf, add content:
```
 add_drivers+=”hv_vmbus hv_netvsc hv_storvsc”
```
Rebuild the initramfs:
```
 # dracut –f -v
```

Install the Azure Linux Agent by running the following command:

 # sudo yum install WALinuxAgent
 # sudo systemctl enable waagent

Do not create swap space on the OS disk.

The Azure Linux Agent can automatically configure swap space using the local resource disk that is attached to the VM after provisioning on Azure. Note that the local resource disk is a temporary disk, and might be emptied when the VM is deprovisioned. After installing the Azure Linux Agent (see previous step), modify the following parameters in /etc/waagent.conf appropriately:
```
 ResourceDisk.Format=y
 ResourceDisk.Filesystem=ext4
 ResourceDisk.MountPoint=/mnt/resource
 ResourceDisk.EnableSwap=y
 ResourceDisk.SwapSizeMB=2048    ## NOTE: set this to whatever you need it to be.
```
Run the following commands to deprovision the virtual machine and prepare it for provisioning on Azure:
```
 # sudo waagent -force -deprovision
 # export HISTSIZE=0
 # logout
```
Click Action -> Shut Down in Hyper-V Manager. Your Linux VHD is now ready to be uploaded to Azure.

Next steps

You're now ready to use your CentOS Linux virtual hard disk to create new virtual machines in Azure. If this is the first time that you're uploading the .vhd file to Azure, see steps 2 and 3 in Creating and uploading a virtual hard disk that contains the Linux operating system.

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Prepare a CentOS-based virtual machine for Azure

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Prepare a CentOS-based virtual machine for Azure

Prerequisites

CentOS 6.x

CentOS 7.0+

Next steps