Comment 4 for bug 1609043

My experience was very similar to that of the Original Reporter, Carles Sentis on 2016-08-02.

After upgrading from 14.4 to 16.4.1, I got a very similar error message:

apt-get: relocation error: /usr/lib/x86_64-linux-gnu/libapt-pkg.so.5.0: symbol _ZNKSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE7compareERKS4_, version GLIBCXX_3.4.21 not defined in file libstdc++.so.6 with link time reference

(Slightly different name of the undefined symbol).

This error-message occurred during boot-up; the system would not run at all!

Fortunately, before doing this upgrade on my main drive, I had done a test-upgrade on a scratch disk.
That one worked just fine. Apparently, I had gotten 16.4 (point nothing)

At first I thought it was a data-transmission error, but (running off the scratch disk), I eventually found other discussions of the same error.

As the error-message indicates, the proximate cause was in the file: /usr/lib/x86_64-linux-gnu/libstdc++.so.6 , which is sym-linked to libstdc++.so.6.0.22 (i.e.: libstdc++.so.6 -> libstdc++.so.6.0.22 ).

On my working scratch disk, the link is to libstdc++.so.6.0.21

When I copied ...0.21 over to my main drive and re-did the link to point to ...0.21 , everything worked again.

I have since had several system updates. Before and after each one, I now check where the /usr/lib/x86_64-linux-gnu/libstdc++.so.6 is linked. On several of them, the link got re-assigned to ...0.22
As soon as I noticed that, I re-did the link by hand.

I found that a very quick way to test and verify that "something is not right" is to launch gedit

When the link was pointing at ...0.22 , gedit would just refuse to open; once I relinked to ...0.21 , it worked as normal.

I don't know why this has not raised screaming fire alarms! This error prevents the system from booting up, as well as inhibiting basic functionality.

I hope to see a fixed libstdc++.so.6.0.23 that fixes the problem. Meanwhile, I will continue to be wary after every system update. ...