GLIBCXX_3.4.20 not found, how to fix this error?

I was having the same problem when trying to run other program, and found a solution on StackOverflow.

Basically, just do the following commands: Firstly, install:

sudo apt-get install libstdc++6

This should already be installed by default, but try it anyway. If it doesn't solve it, just do the following:

sudo add-apt-repository ppa:ubuntu-toolchain-r/test 
sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade

I didn't perform the "dist-upgrade" command, but the ones before solved it for me

It happened to me with anaconda 4.0.0 (as @mjp stated), but the fix for me was to run this command in my environment:

conda install libgcc

I had this issue - it was because Anaconda2 didn't have the GLIBCXX_3.4.20 version of whatever that thing is. Only up to .19, the same as yours.

However, Ubuntu's library did have it. So I just created a softlink/shortcut in the Anaconda library to the actual Linux library containing that GLIBCXX_3.4.20, replacing the previous one, and it worked fine after restarting the python GUI (Spyder).

There should be a folder called libstdc++.so.6 in the Anaconda library, which is here: ~/anaconda2/lib. Within this folder is the versions of the script/library-code-thing, excluding the one that you're missing: GLIBCXX_3.4.20

Follow these steps to solve the issue:

1. go to the right location and backup your current anaconda2 shortcut (change its name so it isn't overwritten):

   cd ~/anaconda2/lib
   mv -vf libstdc++.so.6 libstdc++.so.6.old
   

2. create a new shortcut using the ln command (I am assuming that I am in the previous location ~/anaconda2/lib):

   ln -s /usr/lib/x86_64-linux-gnu/libstdc++.so.6 ./libstdc++.so.6
   

3. restart spyder / other interface you use

It should now work!