Foire Aux Questions à propos det CentOS en général

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1. Pourquoi CentOS existe ?

CentOS existe pour proposer une plate-forme informatique destinée aux entreprises à quiconque souhaite l'utiliser. CentOS 2, 3, 4 et 5 sont construits à partir de SRPMS disponibles publiquement fournis par un éditeur Nord-Américain de distribution Linux reconnu. CentOS est pleinement conforme avec la politique de redistribution de l'éditeur et vise à être 100% compatible. (CentOS ne modifie les paquets logiciels que pour en retirer la marque et les graphismes appartenant à l'éditeur). CentOS est conçu pour des gens ayant besoin d'un système d'exploitation de classe entreprise, sans le coût du logiciel ou du support de l'éditeur. Ni le projet CentOS (nous qui construisons CentOS) ni les versions de CentOS ne sont liés à, produits par, ou supportés par le dit éditeur. Notre logiciel ne contient pas non plus le produit de l'éditeur…bien qu'il soit basé sur les mêmes logiciels libres SRPMS que l'éditeur produit.

2. Combien de temps se passe entre le moment où Red Hat publie un correctif et son apparition dans CentOS ?

Nous essayons de faire que les paquets RPM soient disponibles sur les miroirs dans les 72 heures après leur publication, et ils le sont générallement dans les 24 heures. Il arrive occasionnellement que des paquets soient retardés pour diverses raisons. Rarement, des paquets peuvent être construits et distribués sur les miroirs, tout en étant pas disponibles via yum. (Cela est dû au fait que yum-arch n'a pas été lancé sur le miroir maître. Cela peut arriver quand des problèmes avec les paquets en provenance de l'éditeur sont détectés peu après leur diffusion, et que cette même diffusion empêche le fonctionnement du paquet incriminé.)

Update Sets (see this FAQ) will have Security Errata released was stated above, while the BugFix and Enhancement errata are actually tested more rigorously and released after the new ISO for the Update Set is produced. The goal for release of a new point release or update set is four to eight weeks after the release by upstream. For more details see the explanation of The CentOS Rebuild and Release Process

3. How do I get Updates?

CentOS ships with an application called yum that serves as our recommended tool for performing updates and package installation. Please see PackageManagement, PackageManagement/Yum, and this guide for Managing software with Yum.

A version of up2date is also provided that does not connect to the upstream vendor, but instead connects to the CentOS Network (CN) for updates. CentOS has made a decision to NOT automatically load our RPM-GPG-KEY for CentOS-3, but to allow users to first verify the key and then install it. This will prevent people from modifying our key and installing modified software. In CentOS 4, yum will import the key, but only after the user sees the key and can verify it is authentic.

There is a separate FAQ question concerning how to import the CentOS RPM signature key.

Note on using yum (with CentOS-2 and CentOS-3), the first time you run yum, you may download a large number of header files (100's). These are generally very small files. Yum uses the header files to determine dependencies, packages available for install, etc. Do not be alarmed when this initial download occurs. yum is NOT downloading the packages. After the first update, you will only download new headers. (Note, with CentOS-4 we use a newer version of yum, so there is a new metadata system that has the hdr files compressed in a single file ...)

4. Many RPMs still contain the name redhat, rhel, or rh. Shouldn't these be changed?

This question has an answer on its own page: CentOS Goals.

Additional Text by JohnnyHughes:

• The upstream vendor is using open source (mostly GPL) software in their business model. They take software that other people write (Gnome.org, X.org, KDE.org, OpenOffice.org to name a few). They repackage the source files into RPM format for redistribution. Because they chose an open source model to obtain the software they distribute, they must provide their source code to others. That is how the GPL works. The upstream vendor provides much added value by creating the Source RPMS and distributing them. They also fix problems in software and provide feedback to the software developers ... this is what makes open source software work. The CentOS Project takes the publicly available source packages (SRPMS) provided by the upstream vendor and creates binary (installable) packages for use by anyone who wants to use it. Some packages contain Trademark information and the upstream vendor has specifically created a guide to redistribute software built from their

  publicly available sources. You can read about it here. We support the upstream vendors Trademark rights and strive to be in full compliance with those guide lines. The CentOS project is not interested in taking credit for work done by others, so where possible we will leave all vendor file names as they are. If we must make any changes to a package (due to trademark restrictions, to setup a configuration file, etc.), it will have a .centosx in the filename (the x is the CentOS version ... 3 for CentOS-3.x, 4 for CentOS-4.x, etc.) As do most of the other rebuild projects, we change the kernel SRPM and do not label it .centosx. This is because the kernel needs to be exactly the same name to allow 3rd party modules to function.

  I would like to thank the upstream vendor for making the SRPMS available in the manner that they do. There are several other enterprise vendors who do not make their source as readily available. Their product is excellent (or we would not rebuild it as CentOS), as is their support. If you need the support services that they provide, we highly recommend their enterprise product I would also like to make sure there is no confusion concerning the CentOS Project and the upstream vendor. The CentOS Project is not supported by or affiliated with the upstream vendor in any way. The upstream vendor does not recommend or support any of our offerings in any way.

5. Does CentOS change the upstream Source RPMs?

No. CentOS' key mandate for our base and updates repositories is NOT extending or enhancing packages or features beyond those supplied by the upstream Source RPM's. CentOS strives intentionally to be a simple binary-functional clone for our users. CentOS does offer other (optional) repositories called extras, addons, contribs, and centosplus that do offer added functionality. There is a Wiki page about the various CentOS repositories and their purposes.

6. Is there a Contrib area?

Yes. Please see the Wiki page on Contributing to the CentOS project

7. What is CentOS's relationship with Red Hat®, Inc. or RHEL?

There is none, nada, zip, zero. CentOS-x is NOT a Red Hat®, Inc. or Fedora™ Core affiliated product or project.

The CentOS Project is not affiliated with or supported by Red Hat®, Inc or the Fedora™ Project.

CentOS-x is NOT supported in any way by Red Hat®, Inc. or the Fedora™ Project.

CentOS-x is NOT Red Hat® Linux, it is NOT Fedora™ Core. It is NOT Red Hat® Enterprise Linux. It is NOT RHEL. CentOS-x does NOT contain Red Hat® Linux, Fedora™ Core, or Red Hat® Enterprise Linux.

CentOS is built from publicly available open source SRPMS. See About CentOS if you have any questions.

8. Where can I get package XyZ.rpm for CentOS?

The Wiki has a page about the CentOS and other ''friendly'' repositories. Chances are good that one of those repositories has the package you are looking for.

9. What architectures are supported?

The following architectures are supported by each version of CentOS:

CentOS 2 only supports x86.

CentOS 3 currently supports x86, x86_64 (AMD64 and Intel EM64T), s390, s390x, ia64 (Intel Itanium2).

CentOS 4 currently supports x86, x86_64, s390, s390x and ia64. ppc (PowerPC), alpha (DEC Alpha) and sparc are released in beta for CentOS 4.

CentOS 5 currently supports x86 and x86_64. ia64, ppc (PowerPC) and sparc are being developed.

10. Why does YUM complain about missing a GPG key under CentOS? or I just installed CentOS and yum keeps reporting that the correct GPG key is not installed. How do I install it?

These are answered in the CentOS 3, the CentOS 4 and the CentOS 5 sections of the FAQ.

11. The upstream provider offers Enterprise Linux in several flavors, AS, ES, WS, PWS, etc. Which one is CentOS like?

CentOS is built from the the publicly provided AS Enterprise Sources, although all of the above versions are built from the same sources. AS is either a larger subset of packages (than PWS and WS) or has advanced Kernel parameters supporting larger number of processors or memory (as compared to ES).

With the upstream provider, AS supports some IBM architectures not supported by the other versions (ES, PWS, WS). CentOS is built like the AS version.

Consult: What release am I running?

12. How can I easily compare what major package versions are in CentOS 2, CentOS 3, CentOS 4 and CentOS 5?

On the CentOS Distro Page at DistroWatch.com you can compare Major packages (currently 54) and All tracked packages (currently 177). DistroWatch is an great resource for comparing Linux and BSD distributions.

13. What are all the CentOS repositories (directories) and what is each one for?

addons

Contains packages required in order to build the main Distribution or packages produced by SRPMS built in the main Distribution, but not included in the main Red Hat package tree (mysql-server in CentOS-3.x falls into this category). Packages contained in the addons repository should be considered essentially a part of the core distribution, but may not be in the main Red Hat Package tree.

apt

(CentOS-4 only) Contains all the apt RPMS for the CentOS site. This is where you would point if you want to use apt to do updates. Apt has issues with distros that use multiple libraries, so is only available for the i386 distro.

centosplus

Packages contributed by CentOS Developers and the Users. These packages might replace rpm's included in the core Distribution. You should understand the implications of enabling and using packages from this repository.

contrib

Packages contributed by the CentOS Users, which do not overlap with any of the core Distribution packages. These packages have not been tested by the CentOS developers, and may not track upstream version releases very closely.

docs

Contains manuals and release notes for CentOS

extras

Packages built and maintained by the CentOS developers, that add functionality to the core distribution. These packages have undergone some basic testing, should track upstream release versions fairly closely and will never replace any core distribution package.

isos

Contains the ISOs for download. On the main CentOS mirror sites ISOs can not be downloaded directly, but we provide a Bittorent file for downloading. On external public mirrors, ISOs may or may not be directly downloadable (at the discretion of the mirror owner).

os

Contains the base OS tree that is on the Main ISO files.

updates

Contains updates released for the CentOS distro.

debuginfo

Contains RPMs with debugging symbols generated when the primary packages are built. No repo config is provided. These packages are found at http://debuginfo.centos.org/

testing

This repository is a proving grounds for packages potentially on their way to CentOSPlus and CentOS Extras. They may or may not replace core CentOS packages, and are not guaranteed to function properly. These packages build and install, but are waiting for feedback from testers as to functionality and stability. Packages in this repository will come and go during the development period, so it should not be left enabled or used on production systems without due consideration. No repo config is provided by default. CentOS-Testing.repo can be put in /etc/yum.repos.d. Contribute to CentOS by reporting problems or successes on the CentOS Developer's list. Use with caution.

See the Repositories page for more information.

14. What is the versioning/release scheme of CentOS and how does it compare to the upstream vendor?

The upstream vendor has released 4 versions of enterprise Linux that CentOS rebuilds the freely available SRPMS for (see About CentOS for the details). So, the major CentOS releases are CentOS 2, CentOS 3, CentOS 4 and CentOS 5. The upstream vendor releases security updates as required by circumstances. CentOS releases rebuilds of security updates as soon as possible. Usually within 24 hours (our stated goal is with 72 hours, but we are usually much faster).

The upstream vendor also releases numbered update sets for Version 3, Version 4 and Version 5 of their product (Currently EL 3 update 9, EL 4 update 8 and EL 5.4) 2 to 4 times per year. There are new ISOs from the upstream vendor provided for these update sets. Update sets will be completed as soon as possible after the vendor releases their version ... generally within 2 weeks. CentOS follows these conventions as well, so CentOS 3.9 correlates with EL 3 update 9 and CentOS 4.8 correlates with EL 4 update 8, CentOS 5.4 correlates to EL 5.4, etc.

One thing some people have problems understanding is that if you have any CentOS-3 product and update it, you will be updated to the latest CentOS-3.x version.

The same is true for CentOS-4 and CentOS 5. If you update any CentOS-4 product, you will be updated to the latest CentOS-4.x version, or to the latest CentOS 5.x version if you are updating a CentOS 5 system. This is exactly the same behavior as the upstream product. Let's assume that the latest EL4 product is update 8. If you install the upstream original EL4 CDs (the ones before any update set) and upgrade via their up2date, you will have latest update set installed (EL4 update 8 in our example). Since all updates within a major release (CentOS 2, CentOS 3, CentOS 4, CentOS 5) always upgrade to the latest version when updates are performed (thus mimicking upstream behavior), only the latest version is maintained in each main tree on the CentOS mirrors.

There is a CentOS Vault containing old CentOS trees. This vault is a picture of the older tree when it was removed from the main tree, and does not receive updates. It should only be used for reference.

15. How do I download and burn the CentOS isos?

You can download the latest CentOS ISOs from here: CentOS Downloads

After you download the ISOs, you should check the MD5 sums of the ISO file(s) that you downloaded against the published md5sum list in the ISO directory. If the md5sum values match, the download is good ... if they do not match, the file was not downloaded correctly, and you need to get the file over again. Bittorrent downloads are best, because they do an MD5sum check as part of the download process.

Once you have verified the md5sum of the ISO, you know you have a good download. Now you can burn the ISO to a disk. If you have k3b (CentOS-4 users do, all other CentOS users do not by default) I recommend you use it. You want to use the Tools -> CD -> Burn CD Image or Tools -> DVD -> Burn DVD ISO Image option to write the ISO file to a CD/DVD.

More information on how to verify and burn a CD ISO image can be found at http://www.centos.org/docs/5/html/CD_burning_howto.html.

Once the CD is burned, you should be able to boot from it. The last check you need to do is to verify the media. This will verify that the writing of the ISO to your media happened correctly. There will be a Check Media option after you select your keyboard and language.

If your media passes this check (make sure to check each disc for multiple media sets), you have a fully working installable media. If it fails this check, but passed the md5 check above, then the problem is with the burned media. Try burning on new media at a slower speed, if possible.

All CentOS ISOs that we release have been checked, so if the MD5 sums that you have match, the ISOs should burn clean and pass the media checks. If they do not, the problem is almost always a bad media write to CD/DVD.

If you would rather buy your CentOS ISOs already burned, please see our official CentOS CD/DVD Vendors page. These official CentOS vendors donate a portion of each CD/DVD sale directly to the CentOS Project. You get a tested ISO ready to use ... we get money ... does it get any better than that

16. Can I add X to my server after install? or I installed from the Server ISO and it didn't install X, how do I install X?

The easiest way to install X (and a GUI system) is to use the `yum groupinstall` feature. First you can see all the yum groups available with the command: yum grouplist You can install X and Gnome or KDE like this: yum groupinstall "X Window System" "GNOME Desktop Environment" or yum groupinstall "X Window System" "KDE (K Desktop Environment)" You may also want to add some other groups from the list like `"Graphical Internet" or "Office/Productivity"`

Note: If you are running CentOS 5, yum groupinstall "GNOME Desktop Environment" may complain about a missing libgaim.so.0. This is a known bug. Please see CentOS-5 FAQ for details.

17. What are the Maximum number CPUs, Maximum filesystem size, Minimum / Maximum Memory and other specifications associated with the different CentOS versions?

See this page: CentOS Product Page

18. There is no mp3 support in CentOS! Or is there? How about other multimedia formats?

Yes. There is no mp3 support in CentOS, as there is no mp3 support in the distributions from upstream. It's not included because of legal (patent) issues. You either can encode your music files to ogg vorbis, which is supported in CentOS or install mp3 support from a third party repository, namely rpmforge. For example: If you want mp3 support for xmms, then install xmms-mp3 from that repository.

The same is true for several other multimedia formats (codecs, for example gstreamer plugins) and multimedia players like xine or mplayer. These aren't packaged with CentOS because of legal issues, but you may find those in the rpmforge repository.

19. What is the support ''end of life'' for each CentOS release?

20. Where can I get the latest version of XyZ.rpm for CentOS? I cannot find it anywhere.

CentOS is an Enterprise-class operating system and as such is more about stability and long-term support than cutting edge. Major package versions are retained throughout the life cycle of the product. This is generally what Enterprise wants and affords developers a stable base on which to develop without fear that bespoke applications will break every time something gets upgraded to the latest and greatest, but ultimately buggy version or the API changes breaking backwards compatibility.

So no, you will generally NOT find the very latest versions of various packages included in an Enterprise-class operating system such as CentOS. It's a feature not a deficiency.

Security patches and bug fixes are backported into the shipped version. See here for details: http://www.redhat.com/advice/speaks_backport.html

21. How do I install or update on a system with no network connection?

See the Wiki article Creating Update Media. The technique described there also works with DVD installation media. The key technique is

yum --disablerepo=\* --enablerepo=c5-media <yum_command_and_argument(s)>

22. I installed the x86_64 version, so why do I have i386 packages, and can I get rid of them?

CentOS follows the upstream source in this respect, as it does in general, and the x86_64 installation by default will install iX86 32-bit packages on a 64-bit installation for compatibility purposes. Many server system administrators and some desktop users want a pure 64-bit system and want to remove 32-bit packages. This can be accomplished as follows:

yum remove \*.i\?86

To keep 32-bit packages from being installed in future updates, edit your /etc/yum.conf and add the line:

exclude = *.i?86

Be aware that 32-bit applications, including some browser plugins that may only be available in 32-bit versions, will no longer work after this procedure.