http://en.wikipedia.org/wiki/Scientific_Linux
http://en.wikipedia.org/wiki/CentOS
http://en.wikipedia.org/wiki/Red_Hat_Enterprise_Linux
Let's look at a table comparing when a given CentOS and Scientific Linux release are made after the corresponding RHEL release is made:
| Release | RHEL release day | CentOS release | Scientific Linux |
| 5.6 | 2011/01/13 | NOT DONE YET | NOT DONE YET |
| 6.0 | 2010/11/10 | NOT DONE YET | 2011/03/03 |
| 5.5 | 2010/03/31 | 2010/05/14 | 2010/05/19 |
| 5.4 | 2009/09/02 | 2009/10/21 | 2009/11/04 |
| 4.8 | 2009/05/18 | 2009/08/21 | 2009/07/28 |
| 5.3 | 2009/01/20 | 2009/03/31 | 2009/03/19 |
| 5.2 | 2008/05/21 | 2008/07/17 | 2008/06/26 |
| 4.6 | 2007/11/16 | 2007/12/16 | 2008/09/03 |
| 5.1 | 2007/11/07 | 2007/12/02 | 2008/01/16 |
| 3.9 | 2007/06/15 | 2007/07/26 | 2007/10/12 |
| 5.0 | 2007/03/14 | 2007/04/12 | 2007/05/04 |
| 3.8 | 2006/07/20 | 2006/08/25 | 2006/10/31 |
| 4.0 | 2005/02/14 | 2005/03/09 | 2005/04/20 |
| 3.1 | 2003/10/23 | 2004/03/19 | 2004/05/10 |
Looking at the above table, one can see that while Scientific Linux releases used to come out more slowly than CentOS releases, SL has come out sooner than CentOS or within two weeks of a CentOS release since 2009.
There's more than release dates of iso images, of course. There's also security updates made between releases. CentOS has an issue with not releasing security updates from the time a new version of RHEL is made upstream until they make iso images of the new release. This was an issue back in 2009 and is still an issue today.
A number of important RHEL 5 security updates have not been done for CentOS 5 because they are waiting for CentOS 5.6 to come out first. This means that a number of important and critical security updates are not available for CentOS 5 users.
Scientific Linux, on the other hand, is currently backporting 5.6 security updates in to Scientific Linux 5.5 until they can come out with 5.6 iso images. Indeed, Scientific Linux has a policy to always have someone on hand to make security updates.
There was a recent mailing list posting on the CentOS mailing list showing a number of security problems not fixed in CentOS 5. I went to a mirror showing SL security updates. Every single last security problem listed as not being fixed in CentOS 5 has already been updated in Scientific Linux.
The bottom line is this: Freeloaders are not paying the CentOS development team enough for them to have any obligation to make timely updates to CentOS. Quite frankly, ever since Karanbir Singh (the leading CentOS developer) got married, CentOS releases have been lagging. He's not making enough money with CentOS for it to be worth not being with his wife. I think it’s time for Karanbir to EOL CentOS, pack up his bags, and spend more time with his family.
Scientific Linux, on the other hand is funded by a scientific laboratory with paid developers who can devote time to SL development when it is needed. Security updates are timely; iso images are released about as quickly as they have been with CentOS for the last two years.
It's time for me to switch from CentOS to Scientific Linux.
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