第1步：

[email protected]:~$ gedit ~/.condarc

第2步：

channels:
  - https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/main/
  - https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/free/
  - https://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/conda-forge/
  - https://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/pytorch/
  - https://mirrors.ustc.edu.cn/anaconda/pkgs/main/
  - https://mirrors.ustc.edu.cn/anaconda/pkgs/free/
  - https://mirrors.ustc.edu.cn/anaconda/cloud/conda-forge/
  - https://mirrors.sjtug.sjtu.edu.cn/anaconda/pkgs/main/
  - https://mirrors.sjtug.sjtu.edu.cn/anaconda/pkgs/free/
  - https://mirrors.sjtug.sjtu.edu.cn/anaconda/cloud/conda-forge/
ssl_verify: true
show_channel_urls: true
#changeps1: False

第3步：

save.

第4步：

[email protected]:~$ conda update conda

出现下面的错误：

Solving environment: failed

CondaHTTPError: HTTP 000 CONNECTION FAILED for url <https://mirrors.ustc.edu.cn/anaconda/pkgs/free/linux-64/repodata.json>
Elapsed: -

An HTTP error occurred when trying to retrieve this URL.
HTTP errors are often intermittent, and a simple retry will get you on your way.
SSLError(MaxRetryError('HTTPSConnectionPool(host=\'mirrors.bfsu.edu.cn\', port=443): Max retries exceeded with url: /anaconda/pkgs/free/linux-64/repodata.json (Caused by SSLError(SSLError("bad handshake: Error([(\'SSL routines\', \'ssl3_get_server_certificate\', \'certificate verify failed\')])")))'))

解决方案：

在我查阅了多篇博客，尝试了多种方案之后，终于找到两种解决方案(https://blog.csdn.net/kxqt233/article/details/121167753)：

在命令行中输入conda config --set ssl_verify false修改设置，或者在文件~/.condarc末尾添加一行ssl_verify: false（有则修改即可）
将https改成http
两种方法选一种即可

原因分析
https协议比http协议多了SSL，TLS等验证和加密的阶段，可能是在与清华源进行SSL验证的过程中会出问题，因此需要关掉SSL验证，或者改用http协议。但是使用SSL验证是有助于保障传输过程的可靠性的。
显示现有的源：

conda config --show channels

 又出现如下的问题：

Solving environment: failed

CondaValueError: Malformed version string '~': invalid character(s).

解决方案(https://stackoverflow.com/questions/56084960/condavalueerror-malformed-version-string-invalid-characters)：

I needed to remove conda-forge from my .condarc file. Then everything worked fine.

现在的.condarc文件是：

channels:
  - https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/main/
  - https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/free/
  - https://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/pytorch/
  - https://mirrors.ustc.edu.cn/anaconda/pkgs/main/
  - https://mirrors.ustc.edu.cn/anaconda/pkgs/free/
  - https://mirrors.sjtug.sjtu.edu.cn/anaconda/pkgs/main/
  - https://mirrors.sjtug.sjtu.edu.cn/anaconda/pkgs/free/
ssl_verify: false
show_channel_urls: true

conda设置默认源：

最近由于某些因素清华的conda镜像登不上去了，所以需要换回conda的默认源。查看了conda config的文档后，发现直接删除channels即可。命令如下：

conda config --remove-key channels

Anaconda的默认源：

https://repo.anaconda.com/pkgs/main
https://repo.anaconda.com/pkgs/r
https://repo.anaconda.com/pkgs/msys2

用法：

conda config --add channels https://repo.anaconda.com/pkgs/main
conda config --add channels https://repo.anaconda.com/pkgs/r
conda config --add channels https://repo.anaconda.com/pkgs/msys2
conda config --set show_channel_urls yes