apt-get update fetches and updates the package index. Because I'm used to this way of doing things, I was surprised to find that
yum update does all that and upgrades the system. This made me curious of how to update the package index without installing anything.
While "yum check-update" will refresh the local cache, if it needs to be refreshed, so will most other commands.
The command that's strictly the equivalent of "apt-get update" is "yum makecache" ... however it's generally not recommended to run that directly, in yum.