CentOS 5: Linux for Grownups

Some folks love life on the edge, so they run Debian Unstable, or the newest Ubuntu or Fedora
releases. These are all wonderful Linux distributions, and under most circumstances are reliable enough.
You’ll run into weird dependency issues, or find out the hard way that the latest release of an
application has a few problems, or that the distribution maintainers introduced entirely new applications
that are chock-full of amusing surprises. For the most part they work well, but you never know when
they’re going to get bored and have a little fun at your expense.

Then there are the brave souls who dare to be dull and don’t want surprises. They just want their
systems to chug along and not need a lot of babysitting. For these fine folks there is CentOS Linux.
CentOS is a clone of Red Hat Enterprise Linux (RHEL), built from RHEL’s SRPMs (source RPMs, and please
note the correct absence of apostrophes in RPMs.) It is free of cost, though you might show your
appreciation by clicking the donation link.

CentOS is more than RHEL with the trademarks removed, which in itself is a big job as you’ll see in
the Release Notes. (The CentOS team
are so paranoid about infringing on Red Hat’s trademarks that you’ll find hardly any mentions of “Red
Hat” in the CentOS distribution or on the Web site. Instead, they refer to it as “UOP”, or Upstream
Operating system Provider.) They maintain their own package repositories, and apply security patches as
they receive them from upstream. CentOS supports a range of hardware architectures as this matrix shows. They’re always going to be behind RHEL;
with security fixes they’re right on top of things, and with things like new releases and support for
multiple architectures, they sometimes lag a few weeks behind RHEL. It’s free and it’s binary-compatible
with RHEL, so no complaining allowed.

An important difference between CentOS and RHEL to us lowly users is that RHEL 5 comes in two
editions: Server and Desktop. That’s right, at last they are blatantly using the word “Desktop.” These
are managed via up2date, which CentOS no longer includes, and they have their own separate
repositories that require registration keys to access. Since CentOS is free it makes no sense to maintain
separate repos, so they don’t. No hassles with registration keys; everything is available from a single
source.

Upgrade or Fresh Install

The biggest weakness of RHEL and its clones and offsprings is none of them have a reliable upgrade
path. I’ve heard both success and horror stories on upgrading to new RHEL releases; sometimes it works,
sometimes it doesn’t. In my own experience, trying to upgrade to a new CentOS release has mostly not
worked. This is a good guide for upgrading if
you want to give it a go.

Installer Bad Stuff

Another weakness is a lack of good documentation for a network installation. The official Red Hat
installation manual is sadly deficient, and its offspring and clones are no better. CentOS 5 requires the
first 5 installation CDs for even a base installation with absolutely no extra packages. Yes, really, and
I am pleased that you are as flabbergasted as I am. A nice network installation would remedy this
silliness. The Anaconda installer supports a network installation when you know the secret boot
incantation, which is linux askmethod. Then you get a screen for configuring which CentOS mirror
you want to use. But it doesn’t work, and you won’t know that it’s failed until several steps and many
minutes later in the installation, when it emits a sad “Unable to read package metadata” message. Fedora
tests your network mirrors right away and lets you know if you got it right.

One of the requirements for a network installation is to have both a /base and a /RPM
directory on the installation server, like http://mirror.foosite.org/centos/5/os/i386/base,
whether it’s your own local server or a public mirror. The CentOS public mirrors do not have the
/base directory.

Another gripe about the installer is that it requires at least 512 megabytes of RAM for the graphical
installer, but it does not test for this, so if you don’t have enough RAM it simply locks up at some
random point during the initial screens. To boot to the ncurses-based installer, use linux text.
Be sure to hit the F keys to get useful information before you start.

Good Installer Things

Overall, the CentOS installer is very nice and sensible. You get all kinds of do-overs, so you can
backtrack and make changes. You can configure your network interfaces the way you want, either DHCP or
static addresses. Having to scroll through every single time zone in the world to find the one you want
is a minor pain. I especially liked the package selection screen. It lists the available package groups,
and then to see the individual packages in each group hit F2. Easy and fast.

The default partitioning scheme sets up a logical volume manager. This is the same old Disk Druid
that we know and love, so even if you select one of the pre-fab partitioning schemes you can still change
it all you want. It does not foist Xen and SELinux upon you the way Fedora does, though these are
available if you want them.

Not-Ready-For-Prime-Time Extras

CentOS includes a number of applications that Red Hat calls “Technology Previews.” These are new
applications that are not supported by Red Hat, but since you’re using CentOS you don’t care anyway.
You’ll find a list in the release
notes for RHEL 5
. Two that I found especially interesting are Stateless Linux and Frysk.

Stateless Linux apparently wants to divorce software from hardware, and allow you to magically have
your complete filesystem at any random physical location. OK, so it’s not quite like that. But the goals
are many- central storage and operations while also using local hardware resources intelligently,
mixing-and-matching local and remote filesystems without hassles, automatic hardware configuration,
automatic X Windows configuration, and quick painless migration to a new device. Hey, why not ask for the
moon!

The Frysk real-time monitoring and debugging tool seems similar to the powerful and all-knowing
DTrace in Solaris, only easier to use. Check out this Red Hat magazine article, Frysk: Debugging in
real time
.

Running CentOS

After installation there is a refreshing lack of drama. It just works. I have
a couple of CentOS 4 servers that have not been restarted in over a year; they just keep trundling along.
You might want to tweak your Yum repositories to select geographically close ones, and perform your usual
personal customizations. I like it as a server operating system; it’s rock-solid. It’s also good as an
enterprise desktop for these reasons: mass customized rollouts are dead easy thanks to Kickstart, and
because of RHEL’s conservative approach to software management you’re not likely to be bitten by
half-baked updates.

The CentOS team promise a long support cycle for every release. CentOS 3 will receive maintenance
updates until 2010, CentOS 4 until 2012, and probably 2014 for CentOS 5.

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