# dotnet --list-sdks
Failed to load /usr/share/dotnet/host/fxr/8.0.0/libhostfxr.so, error: /lib64/libstdc++.so.6: version `GLIBCXX_3.4.20' not found (required by /usr/share/dotnet/host/fxr/8.0.0/libhostfxr.so)
The library libhostfxr.so was found, but loading it from /usr/share/dotnet/host/fxr/8.0.0/libhostfxr.so failed
  - Installing .NET prerequisites might help resolve this problem.
     https://go.microsoft.com/fwlink/?linkid=2063370

1. 查看系统版本
strings /usr/lib64/libstdc++.so.6 | grep GLIBCXX
GLIBCXX_3.4
GLIBCXX_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

发现少了GLIBCXX_3.4.20，解决方法是升级libstdc++.

2. 
sudo yum provides libstdc++.so.6
Loaded plugins: fastestmirror, langpacks
Determining fastest mirrors
libstdc++-4.8.5-39.el7.i686 : GNU Standard C++ Library
Repo        : base
Matched from:
Provides    : libstdc++.so.6

3. 
cd /usr/local/lib64
# 下载最新版本的libstdc.so_.6.0.26
sudo wget http://www.vuln.cn/wp-content/uploads/2019/08/libstdc.so_.6.0.26.zip
unzip libstdc.so_.6.0.26.zip
# 将下载的最新版本拷贝到 /usr/lib64
cp libstdc++.so.6.0.26 /usr/lib64
cd  /usr/lib64
# 查看 /usr/lib64下libstdc++.so.6链接的版本
ls -l | grep libstdc++
libstdc++.so.6 ->libstdc++.so.6.0.19
# 删除/usr/lib64原来的软连接libstdc++.so.6，删除之前先备份一份
sudo rm libstdc++.so.6
# 链接新的版本
sudo ln -s libstdc++.so.6.0.26 libstdc++.so.6
# 查看新版本，成功
strings /usr/lib64/libstdc++.so.6 | grep GLIBCXX
...
GLIBCXX_3.4.18
GLIBCXX_3.4.19
GLIBCXX_3.4.20
GLIBCXX_3.4.21
GLIBCXX_3.4.22
GLIBCXX_3.4.23
GLIBCXX_3.4.24
GLIBCXX_3.4.25
GLIBCXX_3.4.26
GLIBCXX_DEBUG_MESSAGE_LENGTH
...

#dotnet --list-sdks
6.0.413 [/usr/share/dotnet/sdk]
7.0.400 [/usr/share/dotnet/sdk]
8.0.100 [/usr/share/dotnet/sdk]