安装java的时候一直提示错误：
[root@localhost ~]# yum -y install java
已加载插件：fastestmirror
Determining fastest mirrors
One of the configured repositories failed (未知),
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=<repoid> …
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 <repoid>
or
subscription-manager repos –disable=<repoid>
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=<repoid>.skip_if_unavailable=true
Cannot find a valid baseurl for repo: epel
网上说的改dns、换源什么的都没有作用，最后发现只要重装epel就可以。
yum -y remove epel-release
yum -y install epel-release