centos7.2のRaspberryPi3でyumができない

こんな症状

yum updateすると以下のエラーが出てしまいます。

# yum update
読み込んだプラグイン:fastestmirror
base                            | 3.6 kB  00:00:00     
http://mirror.centos.org/altarch/7/kernel/armhfp/kernel-%24kvariant/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found
他のミラーを試します。
To address this issue please refer to the below knowledge base article 

https://access.redhat.com/articles/1320623

If above article doesn't help to resolve this issue please create a bug on https://bugs.centos.org/



 One of the configured repositories failed (CentOS Kernels for armhfp),
 and yum doesn't have enough cached data to continue. At this point the only
 safe thing yum can do is fail. There are a few ways to work "fix" this:

     1. Contact the upstream for the repository and get them to fix the problem.

     2. Reconfigure the baseurl/etc. for the repository, to point to a working
        upstream. This is most often useful if you are using a newer
        distribution release than is supported by the repository (and the
        packages for the previous distribution release still work).

     3. Run the command with the repository temporarily disabled
            yum --disablerepo=centos-kernel ...

     4. Disable the repository permanently, so yum won't use it by default. Yum
        will then just ignore the repository until you permanently enable it
        again or use --enablerepo for temporary usage:

            yum-config-manager --disable centos-kernel
        or
            subscription-manager repos --disable=centos-kernel

     5. Configure the failing repository to be skipped, if it is unavailable.
        Note that yum will try to contact the repo. when it runs most commands,
        so will have to try and fail each time (and thus. yum will be be much
        slower). If it is a very temporary problem though, this is often a nice
        compromise:

            yum-config-manager --save --setopt=centos-kernel.skip_if_unavailable=true

failure: repodata/repomd.xml from centos-kernel: [Errno 256] No more mirrors to try.
http://mirror.centos.org/altarch/7/kernel/armhfp/kernel-$kvariant/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found

原因

404を出している http://mirror.centos.org/altarch/7/kernel/armhfp/kernel-%24kvariant/repodata/repomd.xml のURLを見てみると$kvariantがエスケープされてそのまま入っているようです。
この原因はわからなかったのですが、取得先のURL（http://mirror.centos.org/altarch/7/kernel/armhfp/ ）を見てみるとkernel-rpi2/というディレクトリが用意されていました。
自分の端末はRaspBerryPi3ですが、ここを参照させることにしましょう。

解決方法

vi /etc/yum.repos.d/CentOS-armhfp-kernel.repo

[centos-kernel]
name=CentOS Kernels for armhfp
baseurl=http://mirror.centos.org/altarch/7/kernel/$basearch/kernel-$kvariant
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
       file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-SIG-AltArch-Arm32

この
baseurl=http://mirror.centos.org/altarch/7/kernel/$basearch/kernel-$kvariant
を
baseurl=http://mirror.centos.org/altarch/7/kernel/$basearch/kernel-rpi2
に置き換えてました。
再三ですが、RaspBerryPi3ですが、rpi3というディレクトリはないので、rpi2を参照しております。

変更できたら、
yum clean all してから
yum update

で問題なくupdateできるかと思います！