Centos出现源问题解决办法

昨天突然源出现问题，试了好多方法都没有用

出现这个问题

Trying other mirror.

One of the configured repositories failed (CentOS-$releasever - Extras - mirrors.aliyun.com),

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=extras ...

    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 extras

        or

            subscription-manager repos --disable=extras

    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=extras.skip_if_unavailable=true

解决办法

于是我换成了aliyun的镜像，之后无论是执行 yum clean all / yum update 都会有报错

对比.repo文件和报错信息，可以发现$releasever变量没有被系统识别，在连接网络yum源的时候，变成了%24releasever

vim /etc/yum.conf

 我是centos7，使用以下命令修改版本替换信息

%s/$releaserver/7/g          

然后再  yum clean all / yum update