我在R中安装每个包时遇到问题，例如当我输入：
时install.packages("rvest")
我明白了：
Installing package into ‘/home/farzad/R/x86_64-pc-linux-gnu-library/3.2’
(as ‘lib’ is unspecified)
Warning in install.packages :
package ‘rvest’ is not available (for R version 3.2.3)
这是用于安装所有包。我该怎么办？