os-transition.shtml

---
layout: default
title: The HTC System is Transitioning to a Newer Linux Version (CentOS 7)
---

<p>  CHTC staff have upgraded the default operating 
system on our high throughput compute system from 
Scientific Linux 6 (SL6) to a newer and slightly different 
Linux version - CentOS 7.  </p>

<h1>1. Current Status</h1>

<p>
As of May 16, 2019, over 95% of our HTC system is running CentOS 7. We 
have a few "legacy servers" running Scientific Linux 6, including one 
build server.</p>

<h1>2. Default Operating System</h1>

<p>As of May 16, 2017, CHTC-managed submit servers automatically add a 
requirement to jobs that requests the now-current operating system, 
CentOS 7.  To override this default, see below: <a href="#request">Requesting a Specific Operating System</a>.</p> 
 
<p>Many jobs in our high throughput
system that were compiled and run on our old operating system (Scientific Linux 6) 
should be able to run effectively on the new operating systems (CentOS 7) without any issues. 
If you experience any issues with your jobs that you cannot diagnose, 
please let CHTC facilitators know 
immediately by emailing chtc@cs.wisc.edu.</p>

<a name="get-started"></a>
<a name="request"></a>
<h1>3. Requesting a Specific Operating System</h1>

<p>If your job requires an older operating system, you can override the 
default requirement that requests servers running CentOS 7.  You can also 
change your job's requirements so that they can run on a variety of operating
systems.</p>

<ul>
<li>To request that your jobs run on <i>both</i> Scientific Linux 6 and CentOS 7, 
add the following requirements line to your submit file: 

<pre class="sub">requirements = (OpSysMajorVer == 6) || (OpSysMajorVer == 7)</pre>

The advantage of this option is that you may be able to access a larger number 
of computers in CHTC.  Note that code compiled on a newer version of Linux 
may not run older versions 
of Linux.  Make sure to test your jobs specifically on both CentOS 7 (our default) and
Scientific Linux 6 (using the option below) before using the option above. 
</li>

<li>To request that your jobs run on Scientific Linux 6 <i>only</i> 
add the following requirements line to your submit file: 

<pre class="sub">requirements = (OpSysMajorVer == 6)</pre>

Note that using this version of Linux only will severely limit the number 
of servers available to run your jobs, as nearly our entire system is running
a newer version of Linux.  If you have questions about this or how to get your 
jobs to run on a newer version of Linux, talk to CHTC's Research Computing 
Facilitators: <a href="{{ '/get-help' | relative_url}}">contact us or stop by office hours</a>.
</li>
</ul>

<blockquote>
<b>Combining Requirements</b><br>

Does your job already have a requirements statement?  If so, you can 
add the requirements above to the pre-existing requirements by using the 
characters <code>&&</code>.  For example, if your jobs already require large data staging: 

<pre class="submit">requirements = (Target.HasCHTCStaging == true) </pre>

You can add the requirements for using Scientific Linux 6 like so: 

<pre class="submit">requirements = (Target.HasCHTCStaging == true) && (OpSysMajorVer == 6)</pre>

</blockquote>