在linux中如何安装yum工具，要特别详细的_服务器知识

1、这里以centos7 linux系统为例进行讲解如何安装yum。首先，运行命令“rpm -qa yum”来查看系统是否已经安装了yum。如果安装了yum则会列出安装的rpm包名，否则输出为空：

2、然后把centos7 linux系统安装光盘插入光驱运行“mount /dev/sr0 /mnt”命令，将光盘挂载到/mnt分区上：

3、利用CD命令，切换路径到光盘中的rpm包所在目录Packages，然后输入“ ll | grep yum*centos*”命令查找yum安装包，获取yum安装包的文件名：

4、将查找到的yum安装包文件拷贝到/tmp目录中，这里使用cp命令拷贝：

5、继续使用rpm命令安装程序，运行“rpm -ivh /tmp/yum-3.4.3-158.el7.centos.noarch.rpm”命令，开始安装yum程序。其中i参数表示进行安装，v参数表示显示安装详细过程，h参数表示显示安装进程：

6、最后在终端窗口中运行yum命令，可以看到yum命令能够正常运行。以上就是linux中安装yum工具的流程：

修改yum源配置文件，删除yum源，又重新在另一台主机上复制了无问题的yum配置文件，导致yum源无法使用。

yum报错如下

[root@java152 ~]# yum makecache

已加载插件：fastestmirror

Loading mirror speeds from cached hostfile

* base: mirrors.tencentyun.com

* extras: mirrors.tencentyun.com

* updates: mirrors.tencentyun.com

http://mirrors.tencentyun.com/centos/%24releasever/os/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found

#####报错信息是%24releasever 和404，意思就是无法解析腾讯云的$releasever变量。

To address this issue please refer to the below wiki article

https://wiki.centos.org/yum-errors

If above article doesn't help to resolve this issue please use https://bugs.centos.org/.

base | 1.0 kB 00:00:00

http://mirrors.tencentyun.com/centos/%24releasever/os/x86_64/repodata/repomd.xml: [Errno -1] Error importing repomd.xml for base: Damaged repomd.xml file

正在尝试其它镜像。

http://mirrors.tencentyun.com/centos/%24releasever/os/x86_64/repodata/repomd.xml: [Errno 12] Timeout on http://mirrors.tencentyun.com/centos/$releasever/os/x86_64/repodata/repomd.xml: (28, 'Connection timed out after 30000 milliseconds')

正在尝试其它镜像。

One of the configured repositories failed (CentOS-$releasever - Base - 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=base ...

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 base

subscription-manager repos --disable=base

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=base.skip_if_unavailable=true

failure: repodata/repomd.xml from base: [Errno 256] No more mirrors to try.

http://mirrors.aliyun.com/centos/$releasever/os/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found

http://mirrors.tencentyun.com/centos/$releasever/os/x86_64/repodata/repomd.xml: [Errno -1] Error importing repomd.xml for base: Damaged repomd.xml file

http://mirrors.tencentyun.com/$releasever/os/x86_64/repodata/repomd.xml: [Errno 12] Timeout on http://mirrors.tencentyun.com/centos/$releasever/os/x86_64/repodata/repomd.xml: (28, 'Connection timed out after 30000 milliseconds')

http://mirrors.tencentyun.com/centos/$releasever/os/x86_64/repodata/repomd.xml: [Errno 12] Timeout on http://mirrors.tencentyun.com/centos/$releasever/os/x86_64/repodata/repomd.xml: (28, 'Connection timed out after 30001 milliseconds')

1.查看DNS没有问题，且主机可以访问到外网。

在这里插入图片描述

2.重装yum服务，还是不能用。

yum-3.4.3-161.el7.centos.noarch.rpm

yum-metadata-parser-1.1.4-10.el7.x86_64.rpm

yum-plugin-fastestmirror-1.1.31-50.el7.noarch.rpm

命令：rpm -ivh yum-3.4.3-161.el7.centos.noarch.rpm --nodeps --force //nodeps 强制安装force 避免依赖

命令：rpm -ivh yum-metadata-parser-1.1.4-10.el7.x86_64.rpm --nodeps --force

命令：rpm -ivh yum-plugin-fastestmirror-1.1.31-50.el7.noarch.rpm --nodeps --force

最终解决方法

上边一直提示 404 错误，然后我直接访问

http://mirrors.tencentyun.com/centos/$releasever/os/x86_64/repodata/repomd.xml

发现这个地址打不开

将腾讯yum源仓库的$releasever变量都改为7

命令：vim /etc/yum.repos.d/Centos-Base.repo

vim /etc/yum.repos.d/Centos-Epel.repo

命令：:%s/$releasever/7/g #文本编辑器中的替换命令

在这里插入图片描述

修改完之后执行

# yum makecache # OK

知识扩展：

问题分析一下

1、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。

2、查询资料得知，yum中的变量$releasever是由/etc/yum.conf中的distroverpkg定义的。centos-release为一个rpm包，所谓“distroverpkg=centos-release”的意思，其实是将 $releasever设置为centos-release 这个RPM包的版本号；打开yum的配置文件

vim /etc/yum.conf

在这里插入图片描述

通过rpm可以查询到改软件包并没有被安装：

在这里插入图片描述

解决思路

由于centos-release依赖关系比较复杂，约40个左右依赖包，我们可以修改yum源文件，把$releasever全部替换为7（上边已操作），修改以下爱两个配置文件。

# vim /etc/yum.repos.d/Centos-Base.repo # 修改腾讯内部yum源Base仓库

# vim /etc/yum.repos.d/Centos-Epel.repo# 修改腾讯内部yum源EPEL源仓库

在这里插入图片描述

此时yum可以正常使用，通过yum安装centos-release

命令：yum -y install centos-release

下载完centos-release源之后，再将base和epel源的7改回$releasever。yum makecache制作缓存yum即可恢复使用。

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在linux中如何安装yum工具，要特别详细的

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