public void setDefaultOs(String defaultOs) {
        this.defaultOs = defaultOs;
    }
<p>
The stack's operating system, which must be set to one of the following:
</p>
<ul>
<li>
<p>
A supported Linux operating system: An Amazon Linux version, such as <code>Amazon Linux 2</code>,
<code>Amazon Linux 2018.03</code>, <code>Amazon Linux 2017.09</code>, <code>Amazon Linux 2017.03</code>,
<code>Amazon Linux 2016.09</code>, <code>Amazon Linux 2016.03</code>, <code>Amazon Linux 2015.09</code>, or
<code>Amazon Linux 2015.03</code>.
</p>
</li>
<li>
<p>
A supported Ubuntu operating system, such as <code>Ubuntu 18.04 LTS</code>, <code>Ubuntu 16.04 LTS</code>,
<code>Ubuntu 14.04 LTS</code>, or <code>Ubuntu 12.04 LTS</code>.
</p>
</li>
<li>
<p>
<code>CentOS Linux 7</code>
</p>
</li>
<li>
<p>
<code>Red Hat Enterprise Linux 7</code>
</p>
</li>
<li>
<p>
A supported Windows operating system, such as <code>Microsoft Windows Server 2012 R2 Base</code>,
<code>Microsoft Windows Server 2012 R2 with SQL Server Express</code>,
<code>Microsoft Windows Server 2012 R2 with SQL Server Standard</code>, or
<code>Microsoft Windows Server 2012 R2 with SQL Server Web</code>.
</p>
</li>
<li>
<p>
A custom AMI: <code>Custom</code>. You specify the custom AMI you want to use when you create instances. For more
information about how to use custom AMIs with OpsWorks, see <a
href="https://docs.aws.amazon.com/opsworks/latest/userguide/workinginstances-custom-ami.html">Using Custom
AMIs</a>.
</p>
</li>
</ul>
<p>
The default option is the stack's current operating system. Not all operating systems are supported with all
versions of Chef. For more information about supported operating systems, see <a
href="https://docs.aws.amazon.com/opsworks/latest/userguide/workinginstances-os.html">OpsWorks Stacks Operating
Systems</a>.
</p>

@param defaultOs
       The stack's operating system, which must be set to one of the following:</p>
       <ul>
       <li>
       <p>
       A supported Linux operating system: An Amazon Linux version, such as <code>Amazon Linux 2</code>,
       <code>Amazon Linux 2018.03</code>, <code>Amazon Linux 2017.09</code>, <code>Amazon Linux 2017.03</code>,
       <code>Amazon Linux 2016.09</code>, <code>Amazon Linux 2016.03</code>, <code>Amazon Linux 2015.09</code>,
       or <code>Amazon Linux 2015.03</code>.
       </p>
       </li>
       <li>
       <p>
       A supported Ubuntu operating system, such as <code>Ubuntu 18.04 LTS</code>, <code>Ubuntu 16.04 LTS</code>,
       <code>Ubuntu 14.04 LTS</code>, or <code>Ubuntu 12.04 LTS</code>.
       </p>
       </li>
       <li>
       <p>
       <code>CentOS Linux 7</code>
       </p>
       </li>
       <li>
       <p>
       <code>Red Hat Enterprise Linux 7</code>
       </p>
       </li>
       <li>
       <p>
       A supported Windows operating system, such as <code>Microsoft Windows Server 2012 R2 Base</code>,
       <code>Microsoft Windows Server 2012 R2 with SQL Server Express</code>,
       <code>Microsoft Windows Server 2012 R2 with SQL Server Standard</code>, or
       <code>Microsoft Windows Server 2012 R2 with SQL Server Web</code>.
       </p>
       </li>
       <li>
       <p>
       A custom AMI: <code>Custom</code>. You specify the custom AMI you want to use when you create instances.
       For more information about how to use custom AMIs with OpsWorks, see <a
       href="https://docs.aws.amazon.com/opsworks/latest/userguide/workinginstances-custom-ami.html">Using Custom
       AMIs</a>.
       </p>
       </li>
       </ul>
       <p>
       The default option is the stack's current operating system. Not all operating systems are supported with
       all versions of Chef. For more information about supported operating systems, see <a
       href="https://docs.aws.amazon.com/opsworks/latest/userguide/workinginstances-os.html">OpsWorks Stacks
       Operating Systems</a>.
aws-java-sdk-opsworks/src/main/java/com/amazonaws/services/opsworks/model/UpdateStackRequest.java