Linux服务器一般不带图形界面，管理员通常都是通过命令行界面直接操作服务器。在日常的管理运维中，经常需要用到github、gist、githubusercontent等网站上的一些内容，也有时需要用到Google上的一些服务，如Google API之类的。然而这些网站大部分都被GFW防火长城屏蔽掉了，GFW用到的屏蔽手段很多，其中DNS污染就是一种。
PS: GFW防火长城并不是真正要拦截所有人，而是大部分人，要想访问墙外，办法总是有的。
在Linux环境下通过各种形式×××可能并不是最佳实践，最简单的方法是通过修改/etc/hosts文件避免国内DNS污染。
可用的hosts文件可以通过github/hosts项目（https://github.com/racaljk/hosts）获取，也可以从备份地址（https://coding.net/u/scaffrey/p/hosts/git）获取。
本文只是为Linux提供了一套简单的工具，通过这个Shell脚本结合crontab，可以实现自动更新hosts文件。虽然github/hosts项目中也提供了修改的工具，但自己写一个也是不错的，既可以锻炼自己，又可以学习和备忘。
此Shell脚本功能：
解析链接文件，用于增删改工作目录下的其他文件，这个是冗余的可选功能，当前Shell脚本不需要这个功能，但因为这个功能可能在其他脚本中比较重要，暂时罗列在此
echo带色显示，用于为用户提供友好的提示，如一般信息用白色，提示信息用蓝色，错误信息用红色，成功信息用绿色，警告信息用×××等
检查是否是root或者sudo，修改hosts文件需要root权限
检查网络连通性和DNS解析是否正常，如果不正常，做出简单诊断和修改DNS为8.8.4.4和114.114.114.114
根据Linux发行版本的不同执行不同的命令（安装必要的软件包，如git），目前支持RHEL、CentOS、Ubuntu、Debian等版本
从github和备份地址两种途径获取并更改hosts文件
检测hosts文件是否添加成功，用curl google判断
脚本运行效果如下：
![wKioL1cVl1LiAtG5AAUWibXIVK8612.jpg]( "Google hosts demo")
脚本最新内容也可以通过github获取：https://github.com/DingGuodong/GoogleHostsFileForLinux
脚本如下：
#!/bin/bash
# Public header
# =============================================================================================================================
# resolve links - $0 may be a symbolic link
PRG="$0"
while [ -h "$PRG" ]; do
ls=`ls -ld "$PRG"`
link=`expr "$ls" : '.*-> \(.*\)$'`
if expr "$link" : '/.*' > /dev/null; then
PRG="$link"
else
PRG=`dirname "$PRG"`/"$link"
fi
done
# Get standard environment variables
PRGDIR=`dirname "$PRG"`
# echo color function
function cecho {
# Usage:
# cecho -red sometext #Error, Failed
# cecho -green sometext # Success
# cecho -yellow sometext # Warning
# cecho -blue sometext # Debug
# cecho -white sometext # info
# cecho -n # new line
# end
while [ "$1" ]; do
case "$1" in
-normal) color="\033[00m" ;;
# -black) color="\033[30;01m" ;;
-red) color="\033[31;01m" ;;
-green) color="\033[32;01m" ;;
-yellow) color="\033[33;01m" ;;
-blue) color="\033[34;01m" ;;
# -magenta) color="\033[35;01m" ;;
# -cyan) color="\033[36;01m" ;;
-white) color="\033[37;01m" ;;
-n) one_line=1; shift ; continue ;;
*) echo -n "$1"; shift ; continue ;;
esac
shift
echo -en "$color"
echo -en "$1"
echo -en "\033[00m"
shift
done
if [ ! $one_line ]; then
echo
fi
}
# end echo color function
# echo color function, smarter
function echo_r () {
#Error, Failed
[ $# -ne 1 ] && return 0
echo -e "\033[31m$1\033[0m"
}
function echo_g () {
# Success
[ $# -ne 1 ] && return 0
echo -e "\033[32m$1\033[0m"
}
function echo_y () {
# Warning
[ $# -ne 1 ] && return 0
echo -e "\033[33m$1\033[0m"
}
function echo_b () {\
# Debug
[ $# -ne 1 ] && return 0
echo -e "\033[34m$1\033[0m"
}
# end echo color function, smarter
WORKDIR=$PRGDIR
# end public header
# =============================================================================================================================
USER="`id -un`"
LOGNAME=$USER
if [ $UID -ne 0 ]; then
echo "WARNING: Running as a non-root user, \"$LOGNAME\". Functionality may be unavailable. Only root can use some commands or options"
fi
# Name: replaceLocalHostsFileAgainstGfw.sh
# Refer to: https://github.com/racaljk/hosts
# Backups: https://coding.net/u/scaffrey/p/hosts/git
# define user friendly messages
header="
Function: Execute this shell script to access Google, etc easily.
Open source software Written by Guodong Ding <dgdenterprise@gmail.com>.
Blog: http://dgd2010.blog.51cto.com/
Github: https://github.com/DingGuodong
Last updated: 2016-4-19
"
check_network_connectivity(){
echo_b "checking network connectivity ... "
network_address_to_check=8.8.4.4
stable_network_address_to_check=114.114.114.114
ping_count=2
ping -c $ping_count $network_address_to_check >/dev/null
retval=$?
if [ $retval -ne 0 ] ; then
if ping -c $ping_count $stable_network_address_to_check >/dev/null;then
echo_g "network to $stable_network_address_to_check succeed! "
echo_y "note: network to $network_address_to_check failed! "
elif ! ip route | grep default >/dev/null; then
echo_r "network is unreachable, gateway is not set."
exit 1
elif ! ping -c2 $(ip route | awk '/default/ {print $3}') >/dev/null; then
echo_r "network is unreachable, gateway is unreachable."
exit 1
else
echo_r "network is blocked! "
exit 1
fi
elif [ $retval -eq 0 ]; then
echo_g "Check network connectivity passed! "
fi
}
check_name_resolve(){
echo_b "checking name resolve ... "
target_name_to_resolve="github.com"
stable_target_name_to_resolve="www.aliyun.com"
ping_count=1
if ! ping -c$ping_count $target_name_to_resolve >/dev/null; then
echo_y "name lookup failed for $target_name_to_resolve with $ping_count times "
if ping -c$ping_count $stable_target_name_to_resolve >/dev/null; then
echo_g "name lookup success for $stable_target_name_to_resolve with $ping_count times "
fi
[ -f /etc/resolv.conf ] && cp /etc/resolv.conf /etc/resolv.conf$(date +%Y%m%d%H%M%S)~
cat >/etc/resolv.conf<<eof
nameserver 8.8.4.4
nameserver 114.114.114.114
eof
check_name_resolve
else
echo_g "Check name resolve passed! "
return
fi
}
command_exists() {
# which "$@" >/dev/null 2>&1
command -v "$@" >/dev/null 2>&1
}
check_command_can_be_execute(){
command_exists
}
yum_install_packages(){
echo_b "yum install $@ ..."
yum -q -yy install $@
retval=$?
if [ $retval -ne 0 ] ; then
echo_r "yum install $@ failed! "
exit 1
else
echo_g "yum install $@ successfully! "
fi
}
apt_get_install_packages(){
echo_b "apt-get install $@ ..."
apt-get -qq -y install $@
retval=$?
if [ $retval -ne 0 ] ; then
echo_r "apt-get install $@ failed! "
exit 1
else
echo_g "apt-get install $@ successfully! "
fi
}
# Refer: https://get.docker.com/
# 'curl -sSL https://get.docker.com/ | sh'
# or:
# 'wget -qO- https://get.docker.com/ | sh'
#
# Check if this is a forked Linux distro
check_linux_distribution_forked() {
# Check for lsb_release command existence, it usually exists in forked distros
if command_exists lsb_release; then
# Check if the `-u` option is supported
set +e
lsb_release -a -u > /dev/null 2>&1
lsb_release_exit_code=$?
set -e
# Check if the command has exited successfully, it means we're in a forked distro
if [ "$lsb_release_exit_code" = "0" ]; then
# Print info about current distro
cat <<-EOF
You're using '$lsb_dist' version '$dist_version'.
EOF
# Get the upstream release info
lsb_dist=$(lsb_release -a -u 2>&1 | tr '[:upper:]' '[:lower:]' | grep -E 'id' | cut -d ':' -f 2 | tr -d '[[:space:]]')
dist_version=$(lsb_release -a -u 2>&1 | tr '[:upper:]' '[:lower:]' | grep -E 'codename' | cut -d ':' -f 2 | tr -d '[[:space:]]')
# Print info about upstream distro
cat <<-EOF
Upstream release is '$lsb_dist' version '$dist_version'.
EOF
else
if [ -r /etc/debian_version ] && [ "$lsb_dist" != "ubuntu" ]; then
# We're Debian and don't even know it!
lsb_dist=debian
dist_version="$(cat /etc/debian_version | sed 's/\/.*//' | sed 's/\..*//')"
case "$dist_version" in
8|'Kali Linux 2')
dist_version="jessie"
;;
7)
dist_version="wheezy"
;;
esac
fi
fi
fi
}
check_linux_distribution(){
# refer to /etc/issue and /etc/*-release maybe more better choice
# perform some very rudimentary platform detection
lsb_dist=''
dist_version=''
if command_exists lsb_release; then
lsb_dist="$(lsb_release -si)"
fi
if [ -z "$lsb_dist" ] && [ -r /etc/lsb-release ]; then
lsb_dist="$(. /etc/lsb-release && echo "$DISTRIB_ID")"
fi
if [ -z "$lsb_dist" ] && [ -r /etc/debian_version ]; then
lsb_dist='debian'
fi
if [ -z "$lsb_dist" ] && [ -r /etc/fedora-release ]; then
lsb_dist='fedora'
fi
if [ -z "$lsb_dist" ] && [ -r /etc/oracle-release ]; then
lsb_dist='oracleserver'
fi
if [ -z "$lsb_dist" ]; then
if [ -r /etc/centos-release ] || [ -r /etc/redhat-release ]; then
lsb_dist='centos'
fi
fi
if [ -z "$lsb_dist" ] && [ -r /etc/os-release ]; then
lsb_dist="$(. /etc/os-release && echo "$ID")"
fi
lsb_dist="$(echo "$lsb_dist" | tr '[:upper:]' '[:lower:]')"
case "$lsb_dist" in
ubuntu)
if command_exists lsb_release; then
dist_version="$(lsb_release --codename | cut -f2)"
fi
if [ -z "$dist_version" ] && [ -r /etc/lsb-release ]; then
dist_version="$(. /etc/lsb-release && echo "$DISTRIB_CODENAME")"
fi
;;
debian)
dist_version="$(cat /etc/debian_version | sed 's/\/.*//' | sed 's/\..*//')"
case "$dist_version" in
8)
dist_version="jessie"
;;
7)
dist_version="wheezy"
;;
esac
;;
oracleserver)
# need to switch lsb_dist to match yum repo URL
lsb_dist="oraclelinux"
dist_version="$(rpm -q --whatprovides redhat-release --queryformat "%{VERSION}\n" | sed 's/\/.*//' | sed 's/\..*//' | sed 's/Server*//')"
;;
fedora|centos)
dist_version="$(rpm -q --whatprovides redhat-release --queryformat "%{VERSION}\n" | sed 's/\/.*//' | sed 's/\..*//' | sed 's/Server*//')"
;;
*)
if command_exists lsb_release; then
dist_version="$(lsb_release --codename | cut -f2)"
fi
if [ -z "$dist_version" ] && [ -r /etc/os-release ]; then
dist_version="$(. /etc/os-release && echo "$VERSION_ID")"
fi
;;
esac
# Check if this is a forked Linux distro
check_linux_distribution_forked
}
# end Refer above
# refer to LNMP, http://lnmp.org/download.html
function Get_OS_Bit(){
if [[ `getconf WORD_BIT` = '32' && `getconf LONG_BIT` = '64' ]] ; then
Is_64bit='y'
else
Is_64bit='n'
fi
}
function Get_Dist_Name(){
if grep -Eqi "CentOS" /etc/issue || grep -Eq "CentOS" /etc/*-release; then
DISTRO='CentOS'
PM='yum'
elif grep -Eqi "Red Hat Enterprise Linux Server" /etc/issue || grep -Eq "Red Hat Enterprise Linux Server" /etc/*-release; then
DISTRO='RHEL'
PM='yum'
elif grep -Eqi "Aliyun" /etc/issue || grep -Eq "Aliyun" /etc/*-release; then
DISTRO='Aliyun'
PM='yum'
elif grep -Eqi "Fedora" /etc/issue || grep -Eq "Fedora" /etc/*-release; then
DISTRO='Fedora'
PM='yum'
elif grep -Eqi "Debian" /etc/issue || grep -Eq "Debian" /etc/*-release; then
DISTRO='Debian'
PM='apt'
elif grep -Eqi "Ubuntu" /etc/issue || grep -Eq "Ubuntu" /etc/*-release; then
DISTRO='Ubuntu'
PM='apt'
elif grep -Eqi "Raspbian" /etc/issue || grep -Eq "Raspbian" /etc/*-release; then
DISTRO='Raspbian'
PM='apt'
else
DISTRO='unknow'
fi
Get_OS_Bit
}
function Get_RHEL_Version(){
Get_Dist_Name
if [ "${DISTRO}" = "RHEL" ]; then
if grep -Eqi "release 5." /etc/redhat-release; then
echo "Current Version: RHEL Ver 5"
RHEL_Ver='5'
elif grep -Eqi "release 6." /etc/redhat-release; then
echo "Current Version: RHEL Ver 6"
RHEL_Ver='6'
elif grep -Eqi "release 7." /etc/redhat-release; then
echo "Current Version: RHEL Ver 7"
RHEL_Ver='7'
fi
fi
}
function Get_ARM(){
if uname -m | grep -Eqi "arm"; then
Is_ARM='y'
fi
}
Install_LSB()
{
if [ "$PM" = "yum" ]; then
yum -y install redhat-lsb
elif [ "$PM" = "apt" ]; then
apt-get update
apt-get install -y lsb-release
fi
}
Get_Dist_Version()
{
Install_LSB
eval ${DISTRO}_Version=`lsb_release -rs`
eval echo "${DISTRO} \${${DISTRO}_Version}"
}
# end refer to http://lnmp.org/download.html
function get_hosts_file_from_backup_site(){
if ! grep github /etc/hosts >/dev/null; then
cp /etc/hosts /etc/hosts$(date +%Y%m%d%H%M%S)~
else
rm -f /etc/hosts
\cp -f hosts/hosts /etc/hosts
fi
wget -q https://coding.net/u/scaffrey/p/hosts/git/raw/master/hosts -O /etc/hosts
if test $? -eq 0 -a -f /etc/hosts; then
echo_g "set hosts file from backup site successfully! "
else
echo_r "set hosts file from backup site failed! "
fi
}
function get_hosts_file_from_github(){
if [ ! -d hosts ]; then
command_exists git && git clone https://github.com/racaljk/hosts.git >/dev/null 2>&1
retval=$?
if [ $retval -ne 0 ] ; then
echo_r "git clone failed! "
get_hosts_file_from_backup_site
return
else
[ -s hosts/hosts ] && echo "git clone successfully! " || exit 1
fi
elif [ -d hosts/.git ]; then
cd hosts
command_exists git && git pull >/dev/null 2>&1
cd ..
else
echo_r "there was a directory named \"hosts\", failed! "
exit 1
fi
if ! grep github /etc/hosts >/dev/null && test hosts/hosts -nt /etc/hosts; then
cp /etc/hosts /etc/hosts$(date +%Y%m%d%H%M%S)~
\cp -f hosts/hosts /etc/hosts
else
rm -f /etc/hosts
\cp -f hosts/hosts /etc/hosts
fi
}
function validate_network_to_outside(){
echo_b "validating hosts file ... "
http_code=$(curl -o /dev/null -m 10 --connect-timeout 10 -s -w "%{http_code}" https://www.google.com.hk/)
if [ $http_code -ne 200 ]; then
echo_g "Replace hosts file succeeded! "
echo
echo_g "Now you can access Google, etc easily! "
else
echo_r "replace hosts file failed! "
exit 1
fi
}
# main function
# Run setup for each distro accordingly, install git here.
cat -<<eof
$header
eof
check_network_connectivity
check_name_resolve
check_linux_distribution
case "$lsb_dist" in
amzn)
;;
'opensuse project'|opensuse)
;;
'suse linux'|sle[sd])
;;
ubuntu)
command_exists git || apt_get_install_packages git
;;
centos)
command_exists git || yum_install_packages git
;;
*)
echo_r "unsupported system type"
exit 1
esac
get_hosts_file_from_github
validate_network_to_outside
一些有用的参考：
修改 hosts 文件的原理是什么？ https://www.zhihu.com/question/19782572
github/hosts项目wiki https://github.com/racaljk/hosts/wiki
tag: Google hosts,Linux访问Google,Linux×××
--end--
