root@localhost ~ # yum search vim
One of the configured repositories failed (Unknown),
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. Disable the repository, 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>
4. 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: base/7-1.1503.el7.centos.2.8/x86_64

root@localhost ~ # yum repolist
repo id                                 repo name                                 status
base/7-1.1503.el7.centos.2.8/x86_64     CentOS-7-1.1503.el7.centos.2.8 - Base     0
extras/7-1.1503.el7.centos.2.8/x86_64   CentOS-7-1.1503.el7.centos.2.8 - Extras   0
updates/7-1.1503.el7.centos.2.8/x86_64  CentOS-7-1.1503.el7.centos.2.8 - Updates  0
repolist: 0

[base]
name=CentOS-$releasever - Base
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os&infra=$infra
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

echo 7 > /etc/yum/vars/releasever

root@localhost ~ # yum repolist
repo id            repo name             status
base/7/x86_64      CentOS-7 - Base       8652
extras/7/x86_64    CentOS-7 - Extras     180
updates/7/x86_64   CentOS-7 - Updates    1275
repolist: 10107

root@localhost ~ # yum search vim
golang-vim.noarch : Vim plugins for Go
vim-X11.x86_64 : The VIM version of the vi editor for the X Window System
vim-common.x86_64 : The common files needed by any version of the VIM editor
vim-enhanced.x86_64 : A version of the VIM editor which includes recent enhancements
vim-filesystem.x86_64 : VIM filesystem layout
vim-minimal.x86_64 : A minimal version of the VIM editor