Today the two-year-old TLS security certificate for cran.r-project.org expired, so suddenly in R you are getting errors running install.packages or update.packages.
The error looks like this:
> update.packages() --- Please select a CRAN mirror for use in this session --- Error in download.file(url, destfile = f, quiet = TRUE) : cannot open URL 'https://cran.r-project.org/CRAN_mirrors.csv' In addition: Warning message: In download.file(url, destfile = f, quiet = TRUE) : InternetOpenUrl failed: 'The date in the certificate is invalid or has expired'
The workaround is simple: choose another repository! For example: