When you try to run follow two command there can be this error showing in the Terminal.
- First you check if the Network connection and Internet works fine.
- Run yum clean all command and try to clean the corrupted repository data
- Try to run the command in the debug mode as below. The you can get the details error message. If it says some URL cannot be acess then try to access that URL from your web browser and check if the URL work URLGRABBER_DEBUG=1 yum update
- If your network environment uses proxy, then check your Linux version configured with correct proxy.
- Check your system date is correct.