1. gpgcheck is the option for whether gpg verification is enabled. 1 means enabled, 0 means not enabled. Generally, it can be turned off.

2. $releasever and $basearch refer to variables, and the actual values ??are not $releasever and $basearch.

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The software installation package in the yum source usually has a gpg signature. Verify the gpg signature. This is to ensure the reliability of the software installation package. However, some new software installation packages cannot pass verification, but if there is indeed no problem, verification needs to be skipped.

$releasever and $basearch are variables in your system. You can check their values ??by using echo $releasever on the Linux command line.