CentOS 4 Offers Strong RHEL Alternative
By: Sean Michael Kerner
Sunday, April 17, 2005 06:02:30 PM EST
URL: http://www.linuxplanet.com/linuxplanet/reviews/5823/1/
Clone-ing Around?
By any number of different measures, Red Hat Enterprise Linux (RHEL) currently is the established leader in the North American enterprise Linux space. Unlike its cousin Fedora (which is free) or its Red Hat Linux ancestors, RHEL can sometimes have an unpalatable cost associated with it (check out this graph on current server subscription costs). Not everyone needs the excellent support offered by Red Hat for RHEL and not everyone can afford to upgrade their systems three times a years with Fedora. What's a penniless admin to do? Send in the clones.
Thanks to Red Hat's commitment to the principles of open source as well as its open source licensed software utilization, clones of RHEL are available. The clones are not deformed knockoffs of RHEL's splendor rather they are shadows of RHEL that offer most of the same packages as RHEL (without Red Hat logos and trademarks) and in at least one case also promise errata updates at a near Red Hat pace (see Figure 1).
Red Hat Enterprise Linux 4 was released on February 14th, CentOS issued its cloned version two weeks later on March 2nd. Since then I've been evaluating CentOS and putting it through its paces to see if it would hold up to its auspicious genetic parent. Though certainly not perfect, CentOS offers a palatable (free) option for those that want/need Enterprise grade stability without enterprise grade support or cost.
Getting CentOS
The best way bar none to get CentOS is via its well-seeded Torrent. I've kept my BitTorrent client (mostly) available for the last month and have been amazed with how both the number of seeds and peers has remained relatively high and constant.
One of the first issues that many CentOS downloaders experienced (myself included) was problems related to getting their burned ISO to pass the CentOS media check (part of the installation process) even though the MD5 checksums matched up. The well-trafficked CentOS mailing list, as well as its discussion forum, was full of posts on the subject.
The problem had to do with how some Windows based CD burning applications (Nero in particular) didn't (for a long list of reasons that the discussions debate at nauseum) burn the ISO in such a way so they could pass the media check, even though MD5 sums from the ISO download were correct. A number of solutions were offered included a possible fix for the ISO's themselves that the CentOS development team could execute; however no such fix (as far as I know) was ever made. As it turns out Fedora had a similar issue at one point with one of its Test releases, that Red Hat was able to fix in their ISOs.
The solution for most is to (a) burn the ISO's on Linux of (b) Don't use Nero on Windows to burn the ISO's (try a non-buffering CD-burning app instead).
Installing CentOS
RHEL 4 is offered in three principal flavors by Red Hat, AS, ES, WS and desktop. CentOS (like Fedora and the legacy Red Hat Linux) is a combination of all of the above and can be installed to create just about any type of installation that you want. The install choices are: Personal Desktop, Workstation, Server, Custom, Minimal and Everything.
For the purposes of testing (and this review), I installed the "Everything" option which from the installation ISO's came in at 6268 MB. It's certainly an impressive and (very) long list of applications and packages and most users would be hard pressed to find any mainstream open source applications that are not available in the mix.
Those that are familiar with Anaconda (Red Hat's GPL'ed installer) will feel right at home. CentOS's Anaconda looks and feels like Red Hat's, without the Red Hat logo. Frankly I'm still amazed why every distro out there just doesn't use Anaconda, it's one of the best (if not the best) GUI installer for Linux ever created.
Red Hat/ CentOS Network Update
One of the most critical aspects of any distribution and in particular an Enterprise distribution is the update mechanism. When I first installed CentOS 4 from the ISO's, the update tool was called Red Hat Network Update (just as it is in RHEL 4). It looked and behaved just like the "real" Red Hat version--without the Red Hat logo (see Figure 2). After I updated it though with Up2date, one of the updates was for the update mechanism and Red Hat Network Update became CentOS Network Update. From a practical point of view, it doesn't really matter that much as the bottom line is that the update network, works and works well. The first update (as you can expect with an "everything" install) is quite large and as best as I was able to determine was a complete and accurate update of everything that Red Hat themselves have updated packages for.
In terms of timing on security as well as Errata updates for CentOS as compared to RHEL4, I found over the past month of use that the two line up quite well. Security updates happened the same day in almost every case, usually within a few hours.
In a good number of examples in fact, CentOS 4 will use the same RPMs as RHEL4 with the same name (another example is a recent MySQL update: mysql-4.1.10a-1.RHEL4.1.i386.rpm). Certainly not all CentOS 4 fixes use the same exact nomenclature as RHEL4 (in some cases "centos4" is appended somewhere in the name) and not all of them are immediate. One recent example is for an up2date bug, which the CentOS update mirrors didn't have until five days later.
The Difference Between CentOS 4 and RHEL 4
There are some apps that you may want to use on CentOS that for whatever reason need to know that RHEL 4 is installed. Thanks to the CentOS community there is a "fix" for this that will make apps think that you're actually running "the real thing."
All you need to do is add a line to the /etc/redhat-release file. The default (type cat /etc/redhat-release) reads CentOS 4.0 (final). Just add "Red Hat Enterprise Linux AS release 4 (Nahant)" and you're likely good to go.
Your file will look like this:
root@localhost ~]# cat /etc/redhat-release CentOS release 4.0 (Final) Red Hat Enterprise Linux AS release 4 (Nahant)
If all you have in your enterprise was a few (say less than 5) servers and you are (or have) a solid technical understanding and don't need additional support (beyond mailing lists and forums) than CentOS is likely a good choice. Certainly the fact that CentOS 4 isn't "certified" for RHEL 4 applications in particular Oracle is also a consideration (if that's your database).
CentOS 4 is currently available for i386, ia64 and x86_64, while RHEL4 is available for those as well as IBM zSeries, POWER series, and S/390 series systems.
When you pay for Red Hat Network, you also have the option of getting Red Hat Network's Management and Provisioning modules that significantly improves an admins ability to properly handle multi-server medium enterprise deployment and management. (Here's a chart on those features.) Certainly if you're running a small shop it's a bit of overkill, and there are always other alternatives (though I don't know of any for Red Hat that are better or easier than Red Hat's own).
Wrapping Up
CentOS 4 is based on RHEL 4 sources and offers a viable alternative for small enterprises that don't need enterprise support, services or certifications. From a technology point of view in a month of heavy testing and usage, I found CentOS 4 to be a reliable and stable OS. The community forums and mailing list are great resources and helped me to solve any issues that I came across.
Likely many CentOS users will fall into the category of Fedora users that need better stability but don't want to pay any more than they are paying for Fedora, i.e. Free. While I'm a huge fan of Fedora, it can be a difficult distribution to put in place and maintain for servers (in my case app and file servers) that you really don't want to have to fully upgrade up to three times a year. I suspect that for many technically adept small enterprise users, CentOS 4 will fit the bill as a stable and reliable enterprise Linux offering.