/etc/yum.conf

Here's a sample /etc/yum.conf file with a complete listing of different sources for alternative packages.
Be careful in using many different unofficial sources at the same time, since there can be conflicts and problem with dependiencies.
Various repositories have to be commented out in order to be used. You can decide to update only GPG checked packages uncommenting the gpgcheck=1 line.
In this case you must import the relative GPG key (rpm --import URL) from the listed URL (note that lines beginning with "## GPG Key run:..." must NOT be uncommented).
The file is based on the excellent work of Maxwell Kanat-Alexander (max at fedorafaq dot org), version dated 30 July 2004 and some addings from other sources (drtbalu on http://www.fedoraforum.org/forum/archive/index.php/t-19862.html).

Generally is not advisable to use too many sources at the same time, because there can be conflicts between dependencies. Besides the reccomended Fedora updates, either use Fedora-Extras + Livna (as in this sample) OR one or more from Freshrpms, Dag, Dries, Atprms.
Jpackages, Macromedia and other single-project sources shouble be usable without problems.

[main]
cachedir=/var/cache/yum
debuglevel=2
logfile=/var/log/yum.log
pkgpolicy=newest
distroverpkg=fedora-release
tolerant=1
exactarch=0
# Added this because some mirrors go down and then retying takes forever.
retries=1
# Uncomment below if you want to autoupdate also the kernel rpms (reboot is necessary to use the new kernel, once installed)
# exclude=kernel*

## Basic Fedora ####################

[base]
name=Fedora Core $releasever - $basearch - Base
baseurl=http://mirror.hiwaay.net/redhat/fedora/linux/core/$releasever/$basearch/os
  http://rpmfind.net/linux/fedora/core/$releasever/$basearch/os
  http://mirror.clarkson.edu/pub/distributions/fedora/linux/core/$releasever/$basearch/os
  http://mirrors.usc.edu/pub/linux/fedora/fedora/fedora/$releasever/$basearch/RPMS.os
#  http://fedora.redhat.com/releases/fedora-core-$releasever
#gpgcheck=1

#[base-debuginfo]
#name=Fedora Core $releasever - $basearch - Debug Info
#baseurl=http://speakeasy.rpmfind.net/linux/fedora/core/$releasever/$basearch/debug
#  http://distro.ibiblio.org/pub/linux/distributions/fedora/linux/core/$releasever/$basearch/debug
#  http://mirror.clarkson.edu/pub/distributions/fedora/linux/core/$releasever/$basearch/debug
#  http://gulus.usherbrooke.ca/pub/distro/fedora/linux/core/$releasever/$basearch/debug
##gpgcheck=1

[updates-released]
name=Fedora Core $releasever - $basearch - Released Updates
baseurl=http://ftp.ens.utulsa.edu/pub/linux/fedora/core/updates/$releasever/$basearch
  http://rpmfind.net/linux/fedora/core/updates/$releasever/$basearch
  http://mirror.clarkson.edu/pub/distributions/fedora/linux/core/updates/$releasever/$basearch
  http://mirrors.usc.edu/pub/linux/fedora/fedora/fedora/$releasever/$basearch/RPMS.updates
#  http://fedora.redhat.com/updates/released/fedora-core-$releasever
#gpgcheck=1

#[updates-testing]
#name=Fedora Core $releasever - $basearch - Unreleased Updates
#baseurl=http://mirrors.usc.edu/pub/linux/fedora/fedora/fedora/$releasever/$basearch/yum/updates-testing
#  http://distro.ibiblio.org/pub/linux/distributions/fedora/linux/core/updates/testing/$releasever/$basearch
#  http://mirror.clarkson.edu/pub/distributions/fedora/linux/core/updates/testing/$releasever/$basearch
#  http://gulus.usherbrooke.ca/pub/distro/fedora/linux/core/updates/testing/$releasever/$basearch
##  http://fedora.redhat.com/updates/testing/fedora-core-$releasever
##gpgcheck=1


## Fedora Extras #####################

[fedora-stable]
name=Fedora.us Extras (Stable)
baseurl=http://mirrors.kernel.org/fedora.us/fedora/fedora/$releasever/$basearch/RPMS.stable
  http://fedora.quicknet.nl/fedora/fedora/$releasever/$basearch/RPMS.stable
  http://mirrors.usc.edu/pub/linux/fedora/fedora/fedora/$releasever/$basearch/RPMS.stable
  http://fedora.mirror.sdv.fr/fedora/fedora/$releasever/$basearch/RPMS.stable
  http://download.fedora.us/fedora/fedora/$releasever/$basearch/RPMS.stable
#gpgcheck=1

[fedora-unstable]
name=Fedora.us Extras (Unstable)
baseurl=http://mirrors.usc.edu/pub/linux/fedora/fedora/fedora/$releasever/$basearch/RPMS.unstable
  http://fedora.mirror.sdv.fr/fedora/fedora/$releasever/$basearch/RPMS.unstable
  http://fedora.quicknet.nl/fedora/fedora/$releasever/$basearch/RPMS.unstable
  http://mirrors.kernel.org/fedora.us/fedora/fedora/$releasever/$basearch/RPMS.unstable
  http://download.fedora.us/fedora/fedora/$releasever/$basearch/RPMS.unstable
#gpgcheck=1

[fedora-testing]
name=Fedora.us Extras (Testing)
baseurl=http://download.fedora.us/fedora/fedora/$releasever/$basearch/RPMS.testing
  http://fedora.quicknet.nl/fedora/fedora/$releasever/$basearch/RPMS.testing
  http://fedora.mirror.sdv.fr/fedora/fedora/$releasever/$basearch/RPMS.testing
  http://mirrors.kernel.org/fedora.us/fedora/fedora/$releasever/$basearch/RPMS.testing
  http://mirrors.usc.edu/pub/linux/fedora/fedora/fedora/$releasever/$basearch/RPMS.testing
#gpgcheck=1

## Livna.org #################

[livna-stable]
name=Livna.org - Fedora Compatible Packages (stable)
baseurl=http://rpm.livna.org/fedora/$releasever/$basearch/yum/stable
  http://livna.cat.pdx.edu/fedora/$releasever/$basearch/yum/stable
#gpgcheck=1
## GPG Key run: rpm --import http://rpm.livna.org/RPM-LIVNA-GPG-KEY

[livna-unstable]
name=Livna.org - Fedora Compatible Packages (unstable)
baseurl=http://rpm.livna.org/fedora/$releasever/$basearch/yum/unstable
  http://livna.cat.pdx.edu/fedora/$releasever/$basearch/yum/unstable
#gpgcheck=1

[livna-testing]
name=Livna.org - Fedora Compatible Packages (testing)
baseurl=http://rpm.livna.org/fedora/$releasever/$basearch/yum/testing
  http://livna.cat.pdx.edu/fedora/$releasever/$basearch/yum/testing
#gpgcheck=1


## Jpackage #############
# JPackage is a GREAT repository for Java Software.
# However, you may have to compile some SRPMs to use it,
# so it's commented out by default. See
#
# For the SRPMs, and for the general details.
#
# Note: JPackage IS compatible with the fedora.us repositories.
# You can use JPackage and fedora.us at the same time, without
# any trouble.

#[jpackage-generic]
#name=JPackage Cross-Platform Packages
#baseurl=http://aleron.dl.sourceforge.net/sourceforge/jpackage/direct_download/1.5/generic/free
#  http://heanet.dl.sourceforge.net/sourceforge/jpackage/direct_download/1.5/generic/free
#  http://umn.dl.sourceforge.net/sourceforge/jpackage/direct_download/1.5/generic/free
#failovermethod=priority
#gpgcheck=1
## GPG Key run: rpm --import http://www.jpackage.org/jpackage.asc

#[jpackage-fedora]
#name=JPackage Fedora Packages
#baseurl=http://aleron.dl.sourceforge.net/sourceforge/jpackage/direct_download/1.5/fedora-$releasever/free
#  http://heanet.dl.sourceforge.net/sourceforge/jpackage/direct_download/1.5/fedora-$releasever/free
#  http://umn.dl.sourceforge.net/sourceforge/jpackage/direct_download/1.5/fedora-$releasever/free
#failovermethod=priority
##gpgcheck=1

## Alternate Repositories ##############################
# Uncomment these to use them -- note that some packages
# from these repositories may conflict with the fedora.us
# packages. If you use these repositories, you may wish to
# comment-out the fedora.us and livna.org repositories.

#[freshrpms]
#name=FreshRPMs
#baseurl=http://ayo.freshrpms.net/fedora/linux/$releasever/$basearch/freshrpms/
#  http://ftp.us2.freshrpms.net/linux/freshrpms/ayo/fedora/linux/$releasever/$basearch/freshrpms/
#gpgcheck=1
## GPG Key run:rpm --import http://freshrpms.net/packages/RPM-GPG-KEY.txt

#[dag]
#name=Dag APT Repository
#baseurl=http://dag.freshrpms.net/fedora/$releasever/en/$basearch/dag
#  http://dag.atrpms.net/fedora/$releasever/en/$basearch/dag/
#  http://ftp.heanet.ie/pub/freshrpms/pub/dag/fedora/$releasever/en/$basearch/dag
#gpgcheck=1
## GPG Key run: rpm --import http://dag.wieers.com/packages/RPM-GPG-KEY.dag.txt

#[dries]
#name=Extra Fedora rpms dries - $releasever - $basearch
#baseurl=http://apt.sw.be/dries/fedora/linux/$releasever/$basearch/dries
#gpgcheck=1
## GPG Key run: rpm --import http://dries.studentenweb.org/ayo/RPM-GPG-KEY.dries.txt

#[spc-production]
#name=Subpop.net (Production)
#baseurl=http://rpms.subpop.net/fedora/linux/$releasever/$basearch/production
#gpgcheck=1
## GPG Key run: rpm --import http://rpms.subpop.net/RPM-GPG-KEY.spc.txt

#[newrpms]
#name=NewRPMs
#baseurl=http://newrpms.sunsite.dk/apt/redhat/en/$basearch/fc$releasever
#  http://newrpms.atrpms.net/apt/redhat/en/$basearch/fc$releasever
#gpgcheck=1
## GPG Key run: rpm --import http://newrpms.sunsite.dk/gpg-pubkey-newrpms.txt

#[atrpms-stable]
#name=ATrpms - Stable (Most Stable)
#baseurl=http://apt.physik.fu-berlin.de/fedora/$releasever/en/$basearch/at-stable
#  http://ftp-stud.fht-esslingen.de/atrpms/download.atrpms.net/fedora/$releasever/en/$basearch/at-stable
#  http://wftp.tu-chemnitz.de/pub/linux/ATrpms/fedora/$releasever/en/$basearch/at-stable
#gpgcheck=1
## GPG Key run: rpm --import http://atrpms.net/RPM-GPG-KEY.atrpms

#[atrpms-good]
#name=ATrpms - Good (2nd Most Stable)
#baseurl=http://ftp-stud.fht-esslingen.de/atrpms/download.atrpms.net/fedora/$releasever/en/$basearch/at-good
#  http://apt.physik.fu-berlin.de/fedora/$releasever/en/$basearch/at-good
#  http://wftp.tu-chemnitz.de/pub/linux/ATrpms/fedora/$releasever/en/$basearch/at-good
#gpgcheck=1

#[atrpms-testing]
#name=ATrpms - Testing (3rd Most Stable)
#baseurl=http://wftp.tu-chemnitz.de/pub/linux/ATrpms/fedora/$releasever/en/$basearch/at-testing
#  http://apt.physik.fu-berlin.de/fedora/$releasever/en/$basearch/at-testing
#  http://ftp-stud.fht-esslingen.de/atrpms/download.atrpms.net/fedora/$releasever/en/$basearch/at-testing
#gpgcheck=1

#[atrpms-bleeding]
#name=ATrpms - Bleeding (Least Stable)
#baseurl=http://apt.physik.fu-berlin.de/fedora/$releasever/en/$basearch/at-bleeding
#  http://ftp-stud.fht-esslingen.de/atrpms/download.atrpms.net/fedora/$releasever/en/$basearch/at-bleeding
#  http://wftp.tu-chemnitz.de/pub/linux/ATrpms/fedora/$releasever/en/$basearch/at-bleeding
#gpgcheck=1

#[li.stable]
#name=Fedora Linux $releasever - i586 - li (stable)
#baseurl=http://apt.ling.li/fedora/$releasever/i586/li
#gpgcheck=1
## GPG Key run: rpm --import http://apt.ling.li/RPM-GPG-KEY.txt

#[li.unstable]
#name=Fedora Linux $releasever - i586 - li (unstable)
#baseurl=http://apt.ling.li/fedora/$releasever/i586/unstable
#gpgcheck=1


## Miscellaneous #####################

[macromedia.mplug.org]
name=macromedia.mplug.org - Flash Plugin
baseurl=http://macromedia.mplug.org/apt/fedora/$releasever
  http://sluglug.ucsc.edu/macromedia/apt/fedora/$releasever
  http://ruslug.rutgers.edu/macromedia/apt/fedora/$releasever
  http://macromedia.rediris.es/apt/fedora/$releasever
#gpgcheck=1
## GPG Key run: rpm --import http://ruslug.rutgers.edu/macromedia/gpg-publickey.txt

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