CentOS7误删自带python2或yum异常导致yum命令不可用的解决方法
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异常场景1
在执行yum命令时，系统无法找到 Python 解释器，因此无法运行 yum 命令，具体异常如下：
yum update -y
-bash: /usr/bin/yum: /usr/bin/python: 坏的解释器: 没有那个文件或目录
原因
这种情况通常出现在升级或安装Python3版本之后，导致python2失效了，或者说python2被卸载了，但是系统中某些组件依赖于旧版本的 Python
检查
/usr/bin/python是否存在，如果不存在，则需要安装Python解释器。否则就是存在，但是不是正确的版本，请将其链接到正确的 Python解释器即可
验证
查看/usr/bin/yum文件内容
#!/usr/bin/python
import sys
try:
import yum
except ImportError:
发现yum服务使用的默认python版本是python2。接着使用命令查看，发现已经没有python文件，那yum文件中指定的/usr/bin/python自然就无效了
[root@administrator .virtualenvs]# ls /usr/bin/python*
/usr/bin/python3
解决方案
注意：由于yum服务默认使用的python2，不能改成python3，以防出现服务依然不可用情况，所以只能安装一个python2
wget https://www.python.org/ftp/python/2.7.7/Python-2.7.7.tgz
cd Python-2.7.7
./configure
make && make install
让Python2与Python3共存
Python2安装好后，查看/usr/bin/目录下是否有python与pip（应该是有，事后Blog记录），没有则手动建立软链接
[root@administrator ~]# ll /usr/bin/python*
lrwxrwxrwx 1 root root 7 3月 7 15:07 /usr/bin/python -> python2
lrwxrwxrwx 1 root root 9 3月 7 15:07 /usr/bin/python2 -> python2.7
-rwxr-xr-x 1 root root 7144 6月 28 2022 /usr/bin/python2.7
lrwxrwxrwx 1 root root 30 3月 7 10:32 /usr/bin/python3 -> /usr/local/python3/bin/python3
[root@administrator ~]# ll /usr/bin/pip*
-rwxr-xr-x 1 root root 221 3月 7 16:10 /usr/bin/pip
-rwxr-xr-x 1 root root 221 3月 7 16:10 /usr/bin/pip2
-rwxr-xr-x 1 root root 221 3月 7 16:10 /usr/bin/pip2.7
-rwxr-xr-x 1 root root 237 3月 7 10:31 /usr/bin/pip3
以建立Python3和pip3的软链接为例：
ln -s /usr/local/python2/bin/python2 /usr/bin/python3
ln -s /usr/local/python2/bin/pip /usr/bin/pip3
添加环境变量配置vim /etc/profile，然后使配置生效：source /etc/profile
export PYTHON_HOME=/usr/local/python3/bin
export PATH=$PATH:$PYTHON_HOME/bin
检查Python3及pip3是否正常
[root@master ~]# python3 -V
Python 3.9.11
[root@master ~]# pip3 -V
pip 23.0.1 from /usr/local/python3/lib/python3.9/site-packages/pip (python 3.9)
最后验证 Python2与Python3共存
[root@administrator ~]# python
Python 2.7.5 (default, Jun 28 2022, 15:30:04)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-44)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>
[root@administrator ~]# python3
Python 3.9.11 (main, Mar 7 2023, 10:30:01)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-44)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>
[root@administrator ~]# pip -V
pip 20.3.4 from /usr/lib/python2.7/site-packages/pip (python 2.7)
[root@administrator ~]# pip3 -V
pip 23.0.1 from /usr/local/python3/lib/python3.9/site-packages/pip (python 3.9)
异常场景2
执行yum命令出现如下异常提示
[root@administrator ~]# 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:
2.6.6 (r266:84292, Mar 7 2023, 14:15:28)
[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
原因
出现这个异常，原因不明，猜测：
1.缺少python2异常
2.yum软件异常
解决方案
先卸载、删除yum残留文件后，从阿里镜像仓库下载Centos7对应系统版本的yum包，然后进行安装
卸载、删除残留文件
强制删除python已安装程序及其关联
rpm -qa|grep python|xargs rpm -ev --allmatches --nodeps
删除残余python文件
whereis python |xargs rm -frv
验证删除，返回为无结果
whereis python
删除现有yum
rpm -qa|grep yum|xargs rpm -ev --allmatches --nodeps
删除残余yum文件
whereis yum |xargs rm -frv
下载系统版本对应的yum包
查看系统信息
[root@administrator ~]# lsb_release -a
LSB Version: :core-4.1-amd64:core-4.1-noarch
Distributor ID: CentOS
Description: CentOS Linux release 7.9.2009 (Core)
Release: 7.9.2009
Codename: Core
下载的包的版本应与系统版本号对应的一致
https://mirrors.aliyun.com/centos/7.9.2009/os/x86_64/Packages/
搜索关键字：yum，找到yum-3.4.3-168.el7.centos.noarch.rpm
下载
wget https://mirrors.aliyun.com/centos/7.9.2009/os/x86_64/Packages/yum-3.4.3-168.el7.centos.noarch.rpm
执行安装yum，提示缺少相关依赖
[root@administrator ~]# rpm -ivh yum-3.4.3-168.el7.centos.noarch.rpm
error: Failed dependencies:
/usr/bin/python is needed by yum-3.4.3-168.el7.centos.noarch
python >= 2.4 is needed by yum-3.4.3-168.el7.centos.noarch
python(abi) = 2.7 is needed by yum-3.4.3-168.el7.centos.noarch
python-iniparse is needed by yum-3.4.3-168.el7.centos.noarch
python-sqlite is needed by yum-3.4.3-168.el7.centos.noarch
python-urlgrabber >= 3.10-8 is needed by yum-3.4.3-168.el7.centos.noarch
rpm-python is needed by yum-3.4.3-168.el7.centos.noarch
yum-metadata-parser >= 1.1.0 is needed by yum-3.4.3-168.el7.centos.noarch
yum-plugin-fastestmirror is needed by yum-3.4.3-168.el7.centos.noarch
根据提示信息，将第一个依赖关键词python 复制到镜像网站查询获取下载地址
下载依赖包
wget https://mirrors.aliyun.com/centos/7.9.2009/os/x86_64/Packages/python-2.7.5-89.el7.x86_64.rpm
执行安装，同时发现又提示依赖
[root@administrator ~]# rpm -ivh python-2.7.5-89.el7.x86_64.rpm
error: Failed dependencies:
libpython2.7.so.1.0()(64bit) is needed by python-2.7.5-89.el7.x86_64
python-libs(x86-64) = 2.7.5-89.el7 is needed by python-2.7.5-89.el7.x86_64
此时将提示缺少的依赖复制到镜像网站查询并下载，注意版本
安装依赖
rpm -ivh python-libs-2.7.5-89.el7.x86_64.rpm
Preparing... ################################# [100%]
Updating / installing...
1:python-libs-2.7.5-89.el7 ################################# [100%]
以此类推，一步一步安装所需要的依赖。
当依赖的包无法安装时，暂时不管，先下载下来。
当所有依赖都下载后，能安装的都安装了，最后一次性安装
使用–nodeps --force参数不考虑依赖包，强制安装
[root@administrator ~]# rpm -ivh *.rpm --nodeps --force
Preparing... ################################# [100%]
Updating / installing...
1:rpm-4.11.3-45.el7 ################################# [ 25%]
2:rpm-python-4.11.3-45.el7 ################################# [ 50%]
3:yum-plugin-fastestmirror-1.1.31-5################################# [ 75%]
4:yum-3.4.3-168.el7.centos ################################# [100%]
完成后，怀着忐忑的请求执行yum命令，特么的成功了！
root@administrator ~]# yum
Configuration file /etc/yum/pluginconf.d/product-id.conf not found
Unable to find configuration file for plugin product-id
Configuration file /etc/yum/pluginconf.d/search-disabled-repos.conf not found
Unable to find configuration file for plugin search-disabled-repos
Configuration file /etc/yum/pluginconf.d/subscription-manager.conf not found
Unable to find configuration file for plugin subscription-manager
Loaded plugins: fastestmirror
You need to give some command
Usage: yum [options] COMMAND
List of Commands:
check Check for problems in the rpmdb
check-update Check for available package updates
clean Remove cached data
deplist List a package's dependencies
distribution-synchronization Synchronize installed packages to the latest available versions
downgrade downgrade a package
erase Remove a package or packages from your system
fs Acts on the filesystem data of the host, mainly for removing docs/lanuages for minimal hosts.
fssnapshot Creates filesystem snapshots, or lists/deletes current snapshots.
groups Display, or use, the groups information
help Display a helpful usage message
history Display, or use, the transaction history
info Display details about a package or group of packages
install Install a package or packages on your system
list List a package or groups of packages
load-transaction load a saved transaction from filename