我正在尝试将我的 fedora 17 安装升级到更新的版本。我尝试过以下方法，均无效：
首先，使用 fedup：
# yum install ./fedup-0.8.1-1.fc20.noarch.rpm
Loaded plugins: langpacks, presto, priorities, refresh-packagekit
Setting up Install Process
Examining ./fedup-0.8.1-1.fc20.noarch.rpm: fedup-0.8.1-1.fc20.noarch
Marking ./fedup-0.8.1-1.fc20.noarch.rpm to be installed
Resolving Dependencies
--> Running transaction check
---> Package fedup.noarch 0:0.8.1-1.fc20 will be obsoleting
--> Processing Dependency: systemd >= 183 for package: fedup-0.8.1-1.fc20.noarch
---> Package preupgrade.noarch 0:1.1.10-2.fc17 will be obsoleted
--> Processing Dependency: preupgrade for package: PackageKit-0.7.6-1.fc17.x86_64
--> Finished Dependency Resolution
Error: Package: PackageKit-0.7.6-1.fc17.x86_64 (@updates)
Requires: preupgrade
Removing: preupgrade-1.1.10-2.fc17.noarch (@koji-override-0/$releasever)
preupgrade = 1.1.10-2.fc17
Obsoleted By: fedup-0.8.1-1.fc20.noarch (/fedup-0.8.1-1.fc20.noarch)
Not found
Error: Package: fedup-0.8.1-1.fc20.noarch (/fedup-0.8.1-1.fc20.noarch)
Requires: systemd >= 183
Installed: systemd-44-24.fc17.x86_64 (@updates)
systemd = 44-24.fc17
Available: systemd-44-8.fc17.i686 (fedora)
systemd = 44-8.fc17
You could try using --skip-broken to work around the problem
** Found 9 pre-existing rpmdb problem(s), 'yum check' output follows:
krb5-devel-1.10.2-12.fc17.x86_64 has missing requires of keyutils-libs-devel
krb5-devel-1.10.2-12.fc17.x86_64 has missing requires of libselinux-devel
libdb-5.3.21-3.fc18.x86_64 is a duplicate with libdb-5.2.36-5.fc17.x86_64
1:openssl-1.0.1c-7.fc18.x86_64 is a duplicate with 1:openssl-1.0.0k-1.fc17.x86_64
rpm-4.10.1-3.fc18.x86_64 is a duplicate with rpm-4.9.1.3-8.fc17.x86_64
rpm-build-libs-4.10.1-3.fc18.x86_64 is a duplicate with rpm-build-libs-4.9.1.3-8.fc17.x86_64
rpm-libs-4.10.1-3.fc18.x86_64 is a duplicate with rpm-libs-4.9.1.3-8.fc17.x86_64
rpm-python-4.10.1-3.fc18.x86_64 is a duplicate with rpm-python-4.9.1.3-8.fc17.x86_64
sqlite-3.7.11-3.fc17.x86_64 is a duplicate with sqlite-3.7.11-2.fc17.x86_64
二、使用yum：
# yum --releasever=21 distro-sync --nogpgcheck
Loaded plugins: langpacks, presto, priorities, refresh-packagekit
Setting up Distribution Synchronization Process
http://yum.postgresql.org/9.3/fedora/fedora-21-x86_64/repodata/repomd.xml: [Errno 14] curl#22 - "The requested URL returned error: 404 Not Found"
Trying other mirror.
Error: failure: repodata/repomd.xml from pgdg93: [Errno 256] No more mirrors to try.
http://yum.postgresql.org/9.3/fedora/fedora-21-x86_64/repodata/repomd.xml: [Errno 14] curl#22 - "The requested URL returned error: 404 Not Found"
所以，我的问题是如何让我厌倦安装，或者如何让 yum 尝试不同的镜像来升级？
不需要回答“不要这样做”或“你不能这样做”。上述方法取自 Fedora 文档：https://fedoraproject.org/wiki/Upgrading_Fedora_using_yum#Upgrading_Fedora_using_yum_directly和https://fedoraproject.org/wiki/FedUp#How_Can_I_Upgrade_My_System_with_FedUp.3F