linux python版本切换alternatives

查看发现linux的python3命令指向alternatives

alternatives是Linux系列操作系统的一个内置命令，即使最小化安装也有该命令，它的主要作用就是版本控制切换，比如，你的系统内有多个Python版本，Python3.8，Python2.7.5，Python3.6,。

[root@santiagod-andible openstack-ansible]# find /usr/bin/ |grep python3 |xargs -i ls -ld {}
-rwxr-xr-x 1 root root 7760 Aug 26  2021 /usr/bin/python3.9
lrwxrwxrwx 1 root root 31 Aug 25  2021 /usr/bin/python3.6 -> /usr/libexec/platform-python3.6
lrwxrwxrwx 1 root root 32 Aug 25  2021 /usr/bin/python3.6m -> /usr/libexec/platform-python3.6m
lrwxrwxrwx 1 root root 25 Aug 10 09:51 /usr/bin/python3 -> /etc/alternatives/python3
lrwxrwxrwx 1 root root 17 Aug 25  2021 /usr/bin/python3.6-config -> python3.6m-config
lrwxrwxrwx 1 root root 39 Aug 25  2021 /usr/bin/python3.6m-config -> /usr/libexec/platform-python3.6m-config
lrwxrwxrwx 1 root root 46 Aug 25  2021 /usr/bin/python3.6m-x86_64-config -> /usr/libexec/platform-python3.6m-x86_64-config
lrwxrwxrwx 1 root root 32 Aug 11 12:46 /usr/bin/python3-config -> /etc/alternatives/python3-config
-rwxr-xr-x 1 root root 57 Aug 26  2021 /usr/bin/python3.9-config
-rwxr-xr-x 1 root root 3616 Aug 26  2021 /usr/bin/python3.9-x86_64-config

查看alternatives发现，这个链接指向又回去了

[root@santiagod-andible openstack-ansible]# find /etc/alternatives/ |grep python3|xargs -i ls -ld {}
lrwxrwxrwx 1 root root 18 Aug 10 09:51 /etc/alternatives/python3 -> /usr/bin/python3.6
lrwxrwxrwx 1 root root 34 Aug 10 09:51 /etc/alternatives/python3-man -> /usr/share/man/man1/python3.6.1.gz
lrwxrwxrwx 1 root root 25 Aug 11 12:46 /etc/alternatives/python3-config -> /usr/bin/python3.6-config

此时我感觉，切换默认python解释器还是通过alternatives稳妥一点，担心直接修改软链接可能会造成版本冲突

切换默认python3

[root@santiagod-andible openstack-ansible]# alternatives --config python

There are 3 programs which provide 'python'.

  Selection    Command
-----------------------------------------------
*+ 1           /usr/libexec/no-python
   2           /usr/bin/python3
   3           /usr/bin/python3.9

Enter to keep the current selection[+], or type selection number: 3
[root@santiagod-andible openstack-ansible]#  alternatives --display python
python - status is manual.
 link currently points to /usr/bin/python3.9