如何在Linux系统使用 alternatives 系统来管理默认的 python 指向。
使用 update-alternatives 来更新这些链接。
以下是步骤将默认的 python 从 python3 切换到 python2：
root@ubuntu1804:~# ls -la /usr/bin/ | grep python
lrwxrwxrwx 1 root root 26 Mar 26 2018 dh_pypy -> ../share/dh-python/dh_pypy
-rwxr-xr-x 1 root root 1056 Apr 16 2018 dh_python2
lrwxrwxrwx 1 root root 29 Mar 26 2018 dh_python3 -> ../share/dh-python/dh_python3
lrwxrwxrwx 1 root root 23 Jul 1 2022 pdb2.7 -> ../lib/python2.7/pdb.py
lrwxrwxrwx 1 root root 23 Jun 29 2022 pdb3.6 -> ../lib/python3.6/pdb.py
lrwxrwxrwx 1 root root 31 Oct 25 2018 py3versions -> ../share/python3/py3versions.py
lrwxrwxrwx 1 root root 26 Mar 26 2018 pybuild -> ../share/dh-python/pybuild
lrwxrwxrwx 1 root root 24 Nov 13 2022 python -> /etc/alternatives/python
lrwxrwxrwx 1 root root 9 Apr 16 2018 python2 -> python2.7
-rwxr-xr-x 1 root root 3624880 Jul 1 2022 python2.7
lrwxrwxrwx 1 root root 33 Jul 1 2022 python2.7-config -> x86_64-linux-gnu-python2.7-config
lrwxrwxrwx 1 root root 16 Apr 16 2018 python2-config -> python2.7-config
lrwxrwxrwx 1 root root 9 Oct 25 2018 python3 -> python3.6
-rwxr-xr-x 2 root root 4530520 Jun 29 2022 python3.6
lrwxrwxrwx 1 root root 33 Jun 29 2022 python3.6-config -> x86_64-linux-gnu-python3.6-config
-rwxr-xr-x 2 root root 4530520 Jun 29 2022 python3.6m
lrwxrwxrwx 1 root root 34 Jun 29 2022 python3.6m-config -> x86_64-linux-gnu-python3.6m-config
lrwxrwxrwx 1 root root 16 Oct 25 2018 python3-config -> python3.6-config
lrwxrwxrwx 1 root root 10 Oct 25 2018 python3m -> python3.6m
lrwxrwxrwx 1 root root 17 Oct 25 2018 python3m-config -> python3.6m-config
lrwxrwxrwx 1 root root 16 Apr 16 2018 python-config -> python2.7-config
lrwxrwxrwx 1 root root 29 Apr 16 2018 pyversions -> ../share/python/pyversions.py
-rwxr-xr-x 1 root root 2971 Jul 1 2022 x86_64-linux-gnu-python2.7-config
lrwxrwxrwx 1 root root 34 Jun 29 2022 x86_64-linux-gnu-python3.6-config -> x86_64-linux-gnu-python3.6m-config
-rwxr-xr-x 1 root root 3283 Jun 29 2022 x86_64-linux-gnu-python3.6m-config
lrwxrwxrwx 1 root root 33 Oct 25 2018 x86_64-linux-gnu-python3-config -> x86_64-linux-gnu-python3.6-config
lrwxrwxrwx 1 root root 34 Oct 25 2018 x86_64-linux-gnu-python3m-config -> x86_64-linux-gnu-python3.6m-config
lrwxrwxrwx 1 root root 33 Apr 16 2018 x86_64-linux-gnu-python-config -> x86_64-linux-gnu-python2.7-config
root@ubuntu1804:~#
- 首先，您需要添加
python2和python3为python的备选选项。
sudo update-alternatives --install /usr/bin/python python /usr/bin/python2.7 1
sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.6 2
这里的数字1和2表示优先级。这意味着 python3.6 的优先级高于 python2.7。
- 使用以下命令来切换默认的
python版本：
sudo update-alternatives --config python
这将会展示一个菜单，让您选择 python 的版本。按照指示，选择您想要的版本，例如 python2.7。
请注意：不推荐在一些特定的系统，如Ubuntu 18.04，中更改默认的 python 指向。这是因为系统的一些工具可能依赖于Python3。所以在执行这些操作之前，请确保了解可能的影响和风险。如果你只是为了某个特定的脚本或项目使用Python2，建议在该脚本或项目中明确使用 /usr/bin/python2.7，而不是更改默认链接。
