The error message you're seeing, "repomd.xml: [Errno 14] HTTPS Error 404 - Not Found," indicates that the system's package manager is encountering issues while trying to access a repository for Cassandra. This typically happens when the repository URL is incorrect or the repository is temporarily down.
Here are some steps to resolve this issue:
1. **Check Repository URL**: Ensure that the repository URL specified in your package manager configuration is correct. Make sure there are no typos, and it's pointing to a valid Cassandra repository.
2. **Update the Repository Configuration**:
For CentOS, RHEL, or similar distributions, you can usually find the repository configuration in a file under `/etc/yum.repos.d/`. Check the Cassandra repository file and verify that it's correctly configured.
3. **Verify Internet Connectivity**: Ensure that your server has a working internet connection. Try accessing the repository URL in a web browser or use `curl` to check if it's accessible.
```bash
curl -I https://repository-url/cassandra/repo
```
4. **Check the Repository Status**: Sometimes repositories go down temporarily. Visit the Cassandra repository website or check any status pages they provide to see if there are any known issues.
5. **Update or Clean Your Package Cache**: If you've previously attempted to install Cassandra, your package manager might have cached repository data. Try cleaning the cache and updating it:
```bash
sudo yum clean all # For YUM
sudo dnf clean all # For DNF
```
Then, try updating your packages:
```bash
sudo yum update # For YUM
sudo dnf upgrade # For DNF
```
6. **Try a Mirror**: If the official Cassandra repository is having issues, you can try using a mirror. Change the repository URL to a mirror that's operational. Make sure to verify the mirror's URL.
7. **Check for Firewall or Proxy Issues**: If your server is behind a firewall or uses a proxy, make sure they are configured correctly and not blocking access to the repository.
8. **Temporary Issue**: Sometimes, repository servers can experience temporary outages. In such cases, waiting for a while and then trying the installation again might resolve the issue.
9. **Use a Different Repository**: If you're still facing issues, you can try installing Cassandra from a different repository or source, such as the DataStax repository.
Remember to adapt these steps to your specific Linux distribution and package manager. If the issue persists, consult the Cassandra community or support for additional assistance.