解决CentOS7下yum命令的异常

造成yum出错的根本原因是由于手动或自动操作导致python2环境异常。
yum是依赖python的而工作，如有重装、升级、删除等操作都可能造成该错误。

## 解决环境配置问题
一般该异常是由于python2版本环境异常导致
报错示例如下
```bash
[root@localhost ~]# yum
  File "/usr/bin/yum", line 30
    except KeyboardInterrupt, e:
                            ^
SyntaxError: invalid syntax
```

### 步骤1：查看可用的python环境
检查是否存在python2版本环境
```bash
[root@localhost ~]# whereis python
python: /usr/bin/python /usr/bin/python3.7 /usr/bin/python.bak /etc/python \
/usr/local/bin/python3.7m /usr/local/bin/python3.7 /usr/local/bin/python3.7m-config \
/usr/local/bin/python3.7-config /usr/local/bin/python /usr/local/lib/python3.7 \
/usr/share/man/man1/python.1.gz
```
如果显示没有可用的python，则需要手动编译安装，推荐编译安装版本：`Python-2.7.5`

**安装步骤**
下载并编译安装python2.7.5
```bash
wget https://www.python.org/ftp/python/2.7.5/Python-2.7.5.tgz
tar -zxf Python-2.7.5.tgz
cd Python-2.7.5
./configure
make -j 16
# 如果当前路径下已存在python2.7目录和文件时会导致安装失败
# rm -rf /usr/local/include/python2.7
make install

echo 'export PATH=$PATH:/usr/local/bin' >> /etc/profile
source /etc/profile
ln -fs /usr/local/bin/python2.7 /usr/bin/python
```
安装完毕后，使用如下命令查询安装版本
```bash
[root@localhost ~]# python  -V
Python 2.7.5
```
安装完后测试还是不可用请参考步骤2

### 步骤2：修改环境头配置

文件：`/usr/bin/yum`
文件：`/usr/libexec/urlgrabber-ext-down`
文件：`/usr/bin/yum-config-manager`

修改上述文件，将第一行改为

```bash
#!/usr/bin/python
```

## 解决no module named问题
当出现该问题时说明yum的python环境中缺少了必要依赖模块
报错示例如下
```bash
[root@localhost ~]# yum install yum
There was a problem importing one of the Python modules
required to run yum. The error leading to this problem was:

No module named yum

Please install a package which provides this module, or
verify that the module is installed correctly.

It's possible that the above module doesn't match the
current version of Python, which is:
2.6.7 (r267:88850, May 13 2022, 12:16:46)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-44)]

If you cannot solve this problem yourself, please go to
the yum faq at:
  http://yum.baseurl.org/wiki/Faq

```

使用如下命令强制安装即可解决

### 1. 使用如下命令下载到本地

若163镜像不可用时，请替换为阿里云镜像即可：https://mirrors.aliyun.com/

```bash
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-2.7.5-89.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-chardet-2.2.1-3.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-devel-2.7.5-89.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-iniparse-0.4-9.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-kitchen-1.1.1-5.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-libs-2.7.5-89.el7.i686.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-libs-2.7.5-89.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-pycurl-7.19.0-19.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-setuptools-0.9.8-7.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-urlgrabber-3.10-10.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/rpm-python-4.11.3-45.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-3.4.3-168.el7.centos.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-aliases-1.1.31-54.el7_8.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-protectbase-1.1.31-54.el7_8.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-updateonboot-1.1.31-54.el7_8.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-utils-1.1.31-54.el7_8.noarch.rpm
```
### 2. 强制安装所有包

当全部下载完毕后，使用如下命令强制安装所有rpm包
```bash
# 注意： 该命令必须到rpm的当前路径执行
rpm -ivh --force --nodeps *.rpm
```
回显如下 
```bash
[root@localhost yuminstall]# rpm -ivh --force --nodeps *.rpm
准备中...                          ################################# [100%]
正在升级/安装...
   1:python-libs-2.7.5-89.el7         ################################# [  6%]
   2:python-2.7.5-89.el7              ################################# [ 11%]
   3:python-chardet-2.2.1-3.el7       ################################# [ 17%]
   4:python-kitchen-1.1.1-5.el7       ################################# [ 22%]
   5:python-iniparse-0.4-9.el7        ################################# [ 28%]
   6:python-pycurl-7.19.0-19.el7      ################################# [ 33%]
   7:python-urlgrabber-3.10-10.el7    ################################# [ 39%]
   8:rpm-python-4.11.3-45.el7         ################################# [ 44%]
   9:yum-metadata-parser-1.1.4-10.el7 ################################# [ 50%]
  10:yum-plugin-fastestmirror-1.1.31-5################################# [ 56%]
  11:yum-3.4.3-168.el7.centos         ################################# [ 61%]
  12:yum-utils-1.1.31-54.el7_8        ################################# [ 67%]
  13:yum-plugin-aliases-1.1.31-54.el7_################################# [ 72%]
  14:yum-plugin-protectbase-1.1.31-54.################################# [ 78%]
  15:yum-updateonboot-1.1.31-54.el7_8 ################################# [ 83%]
  16:python-devel-2.7.5-89.el7        ################################# [ 89%]
  17:python-setuptools-0.9.8-7.el7    ################################# [ 94%]
  18:python-libs-2.7.5-89.el7         ################################# [100%]
```

安装完毕后，再次测试yum指令将显示正常。