Effectively Use Alternatives command for Python

In this Linux tutorial, you will learn how to use Alternatives command to set Python Versions in Linux. #centlinux #linux #python

Problem Statement:

We have two versions of Python Programming Language are already installed on our Rocky Linux 9 server.

Python 3.9 is by default installed on all Red Hat Enterprise Linux 9 operating systems including Minimal installations.

Install Python on Linux:

We have installed Python 3.10 on this machine, and can also install the same by following our previous article: How to install Python 3.10 on Rocky Linux 9

Verify the existance of Python versions by executing following commands.

# python3.9 -V
Python 3.9.14

# python3.10 -V
Python 3.10.4

Alternatives Command Usage:

Linux operating system provides alternatives command to set an active link to a specific command, among all the installed versions of that command.

Use the following command to set an active version of Python.

# alternatives --config python

If the above command returns no output, check whether python is available in commands list known to alternatives.

# alternatives --list
libnssckbi.so.x86_64    auto    /usr/lib64/pkcs11/p11-kit-trust.so
soelim                  auto    /usr/bin/soelim.groff
iptables                auto    /usr/sbin/iptables-nft
ebtables                auto    /usr/sbin/ebtables-nft
arptables               auto    /usr/sbin/arptables-nft
cifs-idmap-plugin       auto    /usr/lib64/cifs-utils/cifs_idmap_sss.so
man                     auto    /usr/bin/man.man-db
ld                      auto    /usr/bin/ld.bfd

You can see that, there is no python command in list. Therefore, you have to add Python in alternatives info base.

Check the location of Python executable files.

# whereis python3.9
python3.9: /usr/bin/python3.9 /usr/lib/python3.9 /usr/lib64/python3.9 /usr/include/python3.9 /usr/share/man/man1/python3.9.1.gz

# whereis python3.10
python3.10: /usr/local/bin/python3.10 /usr/local/lib/python3.10

Note down the location of Python executables from above output and then execute following commands to define Python alternatives.

# alternatives --install /usr/bin/python python /usr/bin/python3.9 1
# alternatives --install /usr/bin/python python /usr/local/bin/python3.10 2

You can now execute following command to set an active version of Python command.

# alternatives --config python

There are 2 programs which provide 'python'.

  Selection    Command
-----------------------------------------------
   1           /usr/bin/python3.9
*+ 2           /usr/local/bin/python3.10

Enter to keep the current selection[+], or type selection number:

Currently, Python3.10 is set as active Python command.

You can verify it by executing following command at Linux bash prompt.

# python -V
Python 3.10.4

Now, change the active version of Python command to 3.9 as follows.

# alternatives --config python

There are 2 programs which provide 'python'.

  Selection    Command
-----------------------------------------------
   1           /usr/bin/python3.9
*+ 2           /usr/local/bin/python3.10

Enter to keep the current selection[+], or type selection number: 1

Check the version of Python command again.

# python -V
Python 3.9.14

Video of Alternatives Command Example:

Conclusion:

In this Linux tutorial, you will learn how to use Alternatives command to set Python Versions in Linux.