主机无法连接，ping不通

安装软件包时，无法获得主机连接。

  [[e-mail] ~]# yum packages
    Warning: failed to download mirrors file (cannot open URL 'https://cran.r-project.org/CRAN_mirrors.csv'); using local file '/usr/share/doc/R-3.5.1/CRAN_mirrors.csv'
    Warning: unable to access index for repository https://mirror.lzu.edu.cn/CRAN/src/contrib:
      cannot open URL 'https://mirror.lzu.edu.cn/CRAN/src/contrib/PACKAGES'
    Warning messages:
    1: In download.file(url, destfile = f, quiet = TRUE) :
      URL 'https://cran.r-project.org/CRAN_mirrors.csv': status was 'Couldn't resolve host name'
    2: packages ‘rJava’, ‘Rcpp’, ‘RJSONIO’, ‘bitops’, ‘digest’, ‘functional’, ‘stringr’, ‘plyr’, ‘reshape2’, ‘dplyr’, ‘R.methodsS3’, ‘caTools’, ‘Hmisc’ are not available (for R version 3.5.1) 

需要添加一个nameserver 和网关，在windows下查找，获得网关信息。编辑vi /etc/resolv.conf文件

[[e-mail] ~]#vi /etc/resolv.conf
# Generated by NetworkManager
# No nameservers found; try putting DNS servers into your
# ifcfg files in /etc/sysconfig/network-scripts like so:
#
# DNS1=xxx.xxx.xxx.xxx
# DNS2=xxx.xxx.xxx.xx
# DOMAIN=“ww.com”
search “DNS后缀”
nameserver  “默认网关”
nameserver “默认网关”

配置好网关后，需要关闭防火墙，重启网络服务

[[e-mail] ~]#service iptables stop

[[e-mail] ~]#service network restart

检查是否成功

[[e-mail] ~]#ping baidu.com