In this post, I would demo how to solve the following error when running a python script:
[email protected]:~# rma Traceback (most recent call last): File "/usr/lib/command-not-found", line 27, in <module> from CommandNotFound.util import crash_guard ModuleNotFoundError: No module named 'CommandNotFound'
2. The problem and solution
2.1 What is the python version and environment variables in my system
Ubuntu 18.04.6 LTS Ubuntu SMP Wed Dec 9 06:57:35 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
2.2 What is in the File /usr/lib/command-not-found?
rma is a python script to analyze redis dump files, it depends on python3, but on my system, there is already a python2 installed, After installing python3, I tried to run rma like this:
[email protected]:~# rma
I got this:
Traceback (most recent call last): File "/usr/lib/command-not-found", line 27, in <module> from CommandNotFound.util import crash_guard ModuleNotFoundError: No module named 'CommandNotFound'
According to Faheem Mitha:
command-not-foundis a python program, which runs when your command is not something found on the system. (Its function is to suggest alternatives and corrections in case of mistyping etc.) See
/usr/bin/command-not-found. It is trying to import the
CommandNotFoundmodule and is unable to, clearly pointing to a screwed up python installation
2.3 How to solve the problem?
2.3.2 Solution #1
It seems that python can not find packages, so we need to change the env:
PYTHONPATH is an environment variable which you can set to add additional directories where python will look for modules and packages. For most installations, you should not set these variables since they are not needed for Python to run. Python knows where to find its standard library.
Check and verify the PYTHONPATH environemental variable:
2.3.2 Solution #2
Or we can just remove the
not found module:
apt-get remove command-not-found
2.3.3 Solution #3
This error can be fixed by changing the first line of
Make sure the python verison is aligned with your system.
The first line in a python script is the “shebang” line. When you execute a script file from the shell, the shell tries to run the file using the command specified on the shebang line. The ! is called the “bang”. The # is not called the “she”, so sometimes the “shebang” line is also called the “hashbang”.
Why do we need the first line of python script?
By specifying #!/usr/bin/python you specify exactly which interpreter will be used to run the script on a particular system. This is the hardcoded path to the python interpreter for that particular system. The advantage of this line is that you can use a specific python version to run your code.
2.3.4 Solution #4
Remove the soft link to python 3:
sudo rm -rf /usr/bin/python3
Then recreate the soft link to python 3.8 installation:
sudo ln -s /usr/bin/python3.8 /usr/bin/python3
2.4 Why did this problem occur?
According to :
After I opened the
/usr/lib/command-not-found, I realized this error is due to system executing this script using the newly installed python3.5.0, because installing Python3.5.0 creates leads the system to use it when you type in
This error is caused by the screwed up python installations. For me, the problem occurred after installing the python3 on my ubuntu system.
In this post, I tried to demonstrate how to fix the
ModuleNotFoundError: No module named 'CommandNotFound' when running any python script , the key point is to organize your python installations , do not mess it up. That’s it, thanks for your reading.