package ‘RPMM’ is not available (for R version 3.6.0)

When we install some R R package boot time prompt:

Warning: unable to access index for repository https://mirrors.eliteu.cn/CRAN/src/contrib:
  cannot open URL 'https://mirrors.eliteu.cn/CRAN/src/contrib/PACKAGES'
Warning message:
package ‘RPMM’ is not available (for R version 3.6.0)

Execute the following command

setRepositories(addURLs = c(CRANxtras = "http://cran.at.r-project.org/"))

In the implementation of install.packages ( "package_name")

There is a time when the safety switch and then select the source: Select (HTTP mirrors) This is because, centos network can not access https only http access to the source caused