yum update

[root@localhost ~]# yum update
Loaded plugins: langpacks, product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subsc
ription-manager to register.
Repository base is listed more than once in the configuration
base                                                        | 3.6 kB  00:00:00

 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: extras/$releasever/x86_64

原因：/etc/yum.repos.d/文件夹下多了一些不是自己设置的.repo文件，将其删除即可，只需要留下自己配置的本地yum源和163源等。

[root@localhost yum.repos.d]# yum update
Loaded plugins: langpacks, product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subsc
ription-manager to register.
base                                                        | 3.6 kB  00:00:00
(1/2): base/x86_64/group_gz                                 | 166 kB  00:00:02
(2/2): base/x86_64/primary_db                               | 6.0 MB  00:00:04
Resolving Dependencies
--> Running transaction check
---> Package ModemManager-glib.x86_64 0:1.1.0-6.git20130913.el7 will be updated
---> Package ModemManager-glib.x86_64 0:1.6.10-1.el7 will be an update

......

2、中止 yum update

Ctrl+z    #中断当前安装显示

[root@localhost yum.repos.d]# ps -ef|grep yum    #查看yum进程
root      16853   7260 19 23:19 pts/0    00:02:35 /usr/bin/python /bin/yum update
root      16948   7260 34 23:32 pts/0    00:00:01 grep --color=auto yum
[root@localhost yum.repos.d]# kill -9 16853   #杀掉 yum update 进程id
[root@localhost yum.repos.d]#