alternatives 使用笔记

fedora23 X64 系统里有多个版本的 python ，默认使用的是
python2.7

$ ls -l /usr/bin/python*
lrwxrwxrwx. 1 root root    24 Mar 26 15:49 /usr/bin/python -> /usr/bin/python2
lrwxrwxrwx. 1 root root     9 Jun 20  2016 /usr/bin/python2 -> python2.7
-rwxr-xr-x. 1 root root  7088 Jun 20  2016 /usr/bin/python2.7
lrwxrwxrwx. 1 root root     9 Jun 29  2015 /usr/bin/python3 -> python3.4
-rwxr-xr-x. 2 root root 11184 Jun 29  2015 /usr/bin/python3.4
-rwxr-xr-x. 2 root root 11184 Jun 29  2015 /usr/bin/python3.4m
-rwxr-xr-x. 1 root root   308 Jun 19  2015 /usr/bin/python3-chardetect
-rwxr-xr-x. 1 root root   301 Sep 28  2015 /usr/bin/python3-coverage
-rwxr-xr-x. 1 root root   301 Jun 19  2015 /usr/bin/python3-mako-render
-rwxr-xr-x. 1 root root    43 Jun 19  2015 /usr/bin/python3-pyinotify

　　现在想切换到默认使用 python3.4 ，考虑使用 alternatives
命令，用 alternatives –display python 发现 python 没有在 alternatives 的管理列表，将不同版本的 python 添加到alternatives 下，使用方法 usage:
alternatives –install <link> <name> <path> <priority>

$ alternatives --install /usr/bin/python python /usr/bin/python2.7 1
$ alternatives --install /usr/bin/python python /usr/bin/python3.4 2

　　查看 alternatives –display python

$ alternatives --display python
python - status is auto.
link currently points to /usr/bin/python3.4
/usr/bin/python2.7 - priority 1
/usr/bin/python3.4 - priority 2
Current `best' version is /usr/bin/python3.4.

可以看到已经通过 alternatives 指向了 python3.4　　

$ ls -l /usr/bin/python*
lrwxrwxrwx. 1 root root    24 Mar 26 15:49 /usr/bin/python -> /etc/alternatives/python
lrwxrwxrwx. 1 root root     9 Jun 20  2016 /usr/bin/python2 -> python2.7
-rwxr-xr-x. 1 root root  7088 Jun 20  2016 /usr/bin/python2.7
lrwxrwxrwx. 1 root root     9 Jun 29  2015 /usr/bin/python3 -> python3.4
-rwxr-xr-x. 2 root root 11184 Jun 29  2015 /usr/bin/python3.4
-rwxr-xr-x. 2 root root 11184 Jun 29  2015 /usr/bin/python3.4m
-rwxr-xr-x. 1 root root   308 Jun 19  2015 /usr/bin/python3-chardetect
-rwxr-xr-x. 1 root root   301 Sep 28  2015 /usr/bin/python3-coverage
-rwxr-xr-x. 1 root root   301 Jun 19  2015 /usr/bin/python3-mako-render
-rwxr-xr-x. 1 root root    43 Jun 19  2015 /usr/bin/python3-pyinotify

　　

$ ls -l /etc/alternatives/python
lrwxrwxrwx. 1 root root 18 Mar 26 15:49 /etc/alternatives/python -> /usr/bin/python3.4

　　

注：

update-alternatives 与 alternatives 是同一个命令

$ ls -l /usr/sbin/update-alternatives
lrwxrwxrwx. 1 root root 12 Oct  2  2015 /usr/sbin/update-alternatives -> alternatives

　　[1] https://linuxconfig.org/how-to-change-from-default-to-alternative-python-version-on-debian-linux

 

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