centoslinuxUbuntu
What is the difference between Ubuntu server and CentOS that one version would require six CDs? I have used Ubuntu and it was easy to install but I have read that CentOS was a great distribution (it didn't say why, just impressions.)
I was hoping that someone would comment on why the difference in size between the two and I hope this doesn't start some fight about somebody's favorite distro. Thank you.
There is a wput utility which works the other way from the more known wget.
It can be used to upload your files at a controlled rate.
−−limit−rate=RATE
If you don’t want Wput to eat up all available bandwidth, specify this flag. RATE is a numeric value. The units ’K’ (for KiB) and ’M’ (for MiB) are understood. The upload rate is limited on average, meaning that if you limit the rate to 10K and Wput was just able to send with 5K for the first seconds, it will send (if possible) afterwards more than 10K until the average rate of 10K is fulfilled.
About trickle,
trickle is a userspace bandwidth manager. Currently, trickle supports the shaping of any SOCK_STREAM (see socket(2)) connection established via the socket(2) interface. Furthermore, trickle will not work with statically linked executables, nor with setuid(2) executables.
(Author's Note: This answer refers to RHEL 6 and prior versions. RHEL 7 now has a fully supported upgrade path from RHEL 6, the details of which are at the end.)
To start, I should note that there are two ways to do the in-place upgrade:
linux upgradeany.redhat-release RPM manually, run yum distro-sync (this is oversimplified a bit) and reboot.Method 1 is merely unsupported. Method 2 is for Real Cowboys. In addition to the recommended fresh installs, I have done both of these...
Support has two complementary meanings in our world. The first is that a product has a given feature (e.g. "Postfix supports SMTP"). The second is that the vendor will talk to you about it. Which definition is meant is not always clear from context.
To accomplish a task, you obviously need support in the first sense. Where vendor support comes in is to assist you in resolving issues and giving the vendor feedback as to what features need to exist or be improved. Many sites pay a fortune for vendor support when they have the in-house expertise to resolve any issues that may arise, faster and even cheaper than the vendor could. Whether to buy vendor support is ultimately a business decision you will have to make (or advise management on).
This is what Red Hat says about it:
Red Hat does not support in-place upgrades between any major versions of Red Hat Enterprise Linux. A major version is denoted by a whole number version change. For example, Red Hat Enterprise Linux 5 and Red Hat Enterprise Linux 6 are both major versions of Red Hat Enterprise Linux.
In-place upgrades across major releases do not preserve all system settings, services or custom configurations. Consequently, Red Hat strongly recommends fresh installations when upgrading from one major version to another.
They further warn:
However, note the following limitations before you choose to upgrade your system:
- Individual package configuration files may or may not work after performing an upgrade due to changes in various configuration file formats or layouts.
- If you have one of Red Hat's layered products (such as the Cluster Suite) installed, it may need to be manually upgraded after the Red Hat Enterprise Linux upgrade has been completed.
- Third party or ISV applications may not work correctly following the upgrade.
Of course, they then describe how to do an in-place upgrade via method 1, just in case you really want to do it. The feature exists and Red Hat puts development time into it, so it is supported in that the feature exists. But if something goes wrong, Red Hat will tell you to install fresh; they will not provide vendor support for things that break as a result of the upgrade.
For the record, I've never actually had a problem with an in-place upgrade of a RHEL/CentOS or Fedora system that I couldn't resolve myself. The typical problems come from renamed packages, third party repositories and the occasional version mismatch between the i386 and x86_64 architectures of a package. The installer is a bit better at handling these than yum, I think.
I generally warn people that they should plan on a maintenance window every 3-4 years to update RHEL systems from one major version to the next. While upgrades generally go smoothly, the unexpected can always happen.
For both of your environments, I expect an in-place upgrade would work, though I strongly recommend testing it thoroughly first. P2V a representative sample of the servers and run through the in-place upgrade on the virtual systems to see what problems you're going to run into. You can then plan the actual production upgrade based on better knowledge of what will happen.
For a large deployment such as you have here, consider using Limoncelli's "one-some-many" approach. Upgrade one machine, see what problems occur, solve them, then use lessons learned when upgrading a small batch of machines, repeat the lessons learned thing, then when you believe you have all the kinks worked out, upgrade large batches of them.
At a time like this, I also recommend taking a long hard look at your application deployment process. If it isn't sufficiently automated that you can kick it off with a single command and be reasonably sure that the app will be deployed correctly, then perhaps the developers need to get to work on that. Having such a deployment process would make it much easier to do a fresh installation of the newer version of EL and then deploy onto it.
Debian-based distributions do have a supported in-place upgrade method, and it mostly works, but it is not immune from problems. Lots of things broke for people upgrading from Ubuntu 10.04 LTS to 12.04 LTS via the supported method, for instance. It's not clear that Debian or Canonical are putting a sufficient amount of development time into "supporting" this feature, i.e., making sure it works. And you still actually have to buy vendor support for this distribution if you want someone to hold your hand. So I doubt you will gain much from switching to such a distribution.
You may gain by switching to a rolling-release distribution such as Gentoo or Arch. However, this also doesn't make you immune to problems; it just means you have to deal with the upgrade problems continuously over the life of the server (e.g. whenever you or the developers decide to update something on the system), rather than all at once at a well-planned distribution upgrade time. You also have no vendor to provide support.
The Fedora Project is working on a tool to improve in-place upgrades. They had a tool called preupgrade which was abandoned and replaced with a new tool called fedup beginning with Fedora 18. This was added to RHEL7 and now in-place upgrades have full support, at least from RHEL 6 to RHEL 7. From my own experience I can say that while fedup still has some kinks, it is shaping up to be a very useful tool.
CentOS is also experimenting with a rolling-release type of repository, but it only applies between minor versions (e.g. 6.3-6.4).
Best Answer
CentOS is based on Red Hat Enterprise Linux, which you generally buy on CD and (as Red Hat Linux) pre-dates super fast internet connections, so they ship the same number of CDs that RHEL does. They also makes a "single server CD" up to and including 4.x, and a live CD from 5.x onwards, which you can get from the same source as the five CD ISO set.
Ubuntu Server contains the packages on the CD required to get you installed and cover most cases, and suggests you can install the rest from the network. You can also get DVDs of Ubuntu, but they are primarily just all the different languages all rolled into one.
Using Jigdo you could create more CDs of all the packages you want for offline use.