Can't use apt: libstdc++.so.6: version `GLIBCXX_3.4.20' not found

Solution 1:

You could copy libstdc++.so.6 from another Ubuntu installation.

In a 14.04 virtual machine, I removed libstdc++.so.6 and got the same error as you. Then I copied it from my 16.04 host, and apt worked again. You could use a Live CD for this.

Alternatively, download the the right file for your version:

14.04: https://bsre.stackstorage.com/index.php/s/JVNxNO3HWBA4HSa
16.04: https://bsre.stackstorage.com/index.php/s/L394ttygh55cR1W

Then open a Terminal window using Cntrl + Alt + T

1. Type cd ~/Downloads and press enter
2. Type md5sum libstdc++* and press enter

3. Make sure you see either of the following:

   aa688ac2f4c90a023c2cbd1dd21d4ccc libstdc++1404.so.6 68dbd855c3213cae1a41375c25bf6884 libstdc++1604.so.6

4. Then rename the file using sudo mv libstdc++* libstdc++.so.6
5. Move the file: sudo mv libstdc++.so.6 /usr/lib/x86_64-linux-gnu/