It seems that you are running Centos 7. When issuing the command strings /usr/lib/libstdc++.so.6 | grep GLIBCXX in Centos 7, it shows the following output:

GLIBCXX_3.4
_3.4.1
GLIBCXX_3.4.2
GLIBCXX_3.4.3
GLIBCXX_3.4.4
GLIBCXX_3.4.5
GLIBCXX_3.4.6
GLIBCXX_3.4.7
GLIBCXX_3.4.8
GLIBCXX_3.4.9
GLIBCXX_3.4.10
GLIBCXX_3.4.11
GLIBCXX_3.4.12
GLIBCXX_3.4.13
GLIBCXX_3.4.14
GLIBCXX_3.4.15
GLIBCXX_3.4.16
GLIBCXX_3.4.17
GLIBCXX_3.4.18
GLIBCXX_3.4.19
GLIBCXX_DEBUG_MESSAGE_LENGTH

This means that right now Centos doesn't support the version of glibc (, i.e., GLIBCXX_3.4.20) that is required by the latest version of Skype (v8.9).

If wish to install Skype in Centos at the moment, you can have a look at the nux repo which hosts a precompiled version of skype (probably an older version). Or you could always build the latest glibc from source and then try to install Skype.

Your application MCServer was compiled and linked with different g++ than current for your OS, and ABI is not compatible. You either need to find libstdc++.so.6 for original compiler and set environment variable LD_LIBRARY_PATH accordingly or recompile the app with compiler, that comes with your OS.

Weird thing is that after upgrading to CentOS 7.6... it worked once after the first steam update... then went back to the same error that you get.

If you're deploying on CentOS 7, build on CentOS 7.

Otherwise your runtime dependencies won't match up.

It's possible to ship your Ubuntu's libc and libstdc++ with your application, but you should avoid having to do this, if possible.

Try export LD_LIBRARY_PATH=/usr/local/lib:/usr/lib:/usr/local/lib64:/usr/lib64

I also have built gcc 7.3 from sources. My example program name is consolehost.

I've done following:

>ldd ./consolehost
./consolehost: /lib64/libstdc++.so.6: version `GLIBCXX_3.4.22' not found (required by ./consolehost)
./consolehost: /lib64/libstdc++.so.6: version `GLIBCXX_3.4.21' not found (required by ./consolehost)
        linux-vdso.so.1 =>  (0x00007ffd79916000)
        libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f8458cfc000)
        libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007f84589f4000)
        libm.so.6 => /lib64/libm.so.6 (0x00007f84586f1000)
        libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f84584db000)
        libc.so.6 => /lib64/libc.so.6 (0x00007f8458118000)
        /lib64/ld-linux-x86-64.so.2 (0x0000556169234000)

Then I've investigated that:

>ls -ali /lib64/libstdc++.so.6
37631 lrwxrwxrwx. 1 root root 19 мар 17 06:38 /lib64/libstdc++.so.6 -> libstdc++.so.6.0.19

I've figured out that I need version that fresher that 6.0.19. So

>sudo find / -name "libstdc++.so.6*"
/usr/lib64/libstdc++.so.6
/usr/lib64/libstdc++.so.6.0.19
/usr/share/gdb/auto-load/usr/lib64/libstdc++.so.6.0.19-gdb.py
/usr/share/gdb/auto-load/usr/lib64/libstdc++.so.6.0.19-gdb.pyc
/usr/share/gdb/auto-load/usr/lib64/libstdc++.so.6.0.19-gdb.pyo
/usr/local/lib64/libstdc++.so.6.0.24
/usr/local/lib64/libstdc++.so.6
/usr/local/lib64/libstdc++.so.6.0.24-gdb.py
/home/declspec/gcc_build/stage1-x86_64-pc-linux-gnu/libstdc++-v3/src/.libs/libstdc++.so.6.0.24
/home/declspec/gcc_build/stage1-x86_64-pc-linux-gnu/libstdc++-v3/src/.libs/libstdc++.so.6
/home/declspec/gcc_build/x86_64-pc-linux-gnu/libstdc++-v3/src/.libs/libstdc++.so.6.0.24
/home/declspec/gcc_build/x86_64-pc-linux-gnu/libstdc++-v3/src/.libs/libstdc++.so.6
/home/declspec/gcc_build/prev-x86_64-pc-linux-gnu/libstdc++-v3/src/.libs/libstdc++.so.6.0.24
/home/declspec/gcc_build/prev-x86_64-pc-linux-gnu/libstdc++-v3/src/.libs/libstdc++.so.6

In that moment I need to copy libstdc++.so.6.0.24 to /lib64/ and make new Symbolic link.

sudo mv /lib64/libstdc++.so.6 /lib64/libstdc++.so.6.orig
sudo ln -s /lib64/libstdc++.so.6.0.24 /lib64/libstdc++.so.6

That helps me. Hope that helps to you too. This link decribes GLIBCXX, but I did not understand how this works and what's a porpose (why versions is not enough)

If you don't specifically need this version of libstdc++, you may want to remove the package that cause the issue:

yum remove -y libstdc++-4.8.5-16.el7_4.1.i686

Then run the package installation again:

yum install gdb -y

Usually, this kind of conflicts happen because of 3rd-party repositories. Here is a link on serverfault.com to disable/remove it: How do I remove a repository of yum

Try running yum provides libstdc++ to show you what package provided the library on your system. You can then check if those packages are available for update using yum list available | grep <that package> followed by yum update <that package>.

What is libstdc++.so.6? Is this just a library that gcc ships with?

It’s GCC’s implementation of the C++ Standard Library.

What are all the different GLIBCXX_*? Are these also libraries?

These are version symbols, used to allow the library to remain backward-compatible while still being able to change its API. See What do the multiple GLIBC versions mean in the output of ldd? for details.

Question is why do I have different versions of these libraries in different folders?

The copy in /usr/lib64 is your distribution’s version; the copy in /usr/local/lib64 was installed by something else.

When running gcc how do I tell it to use the 6.0.20 library in /usr/local/lib64 instead of the older one?

You can try building with -L/usr/local/lib64, and running with LD_LIBRARY_PATH=/usr/local/lib64 (if necessary).