Shell脚本：检查Internet连接的正确方法？

我发现脚本说他们检查互联网连接。有些人会检查接口的IP地址，但不会检查Internet连接。我发现有些使用ping的方法是这样的：if [ 'ping google.com -c 4 | grep time' != "" ]; then但是有时候ping可能由于某些原因而挂起（例如，等待某些卡住的IO），因此这可能并不可靠。

关于使用脚本检查Internet连接的正确/可靠方式的任何建议？我需要使用一些软件包吗？

cron例如，它需要能够定期检查，然后在连接断开时执行某些操作，例如调用ifup --force [interface]

测试IPv4连接

如果您的网络允许ping通，请尝试ping 8.8.8.8（由Google运行的服务器）。

if ping -q -c 1 -W 1 8.8.8.8 >/dev/null; then
  echo "IPv4 is up"
else
  echo "IPv4 is down"
fi

测试IP连接和DNS

如果您只想在DNS也正常运行时测试成功，请使用主机名。

if ping -q -c 1 -W 1 google.com >/dev/null; then
  echo "The network is up"
else
  echo "The network is down"
fi

测试网络连接

一些防火墙阻止ping。某些地方有防火墙阻止所有流量，除非通过Web代理。如果要测试Web连接，可以发出HTTP请求。

case "$(curl -s --max-time 2 -I http://google.com | sed 's/^[^ ]*  *\([0-9]\).*/\1/; 1q')" in
  [23]) echo "HTTP connectivity is up";;
  5) echo "The web proxy won't let us through";;
  *) echo "The network is down or very slow";;
esac

我强烈建议您不要使用它ping来确定连接性。由于担心源自其网络的ping Flood攻击，有太多网络管理员禁用了ICMP（它使用的协议）。

相反，我在可以打开的端口上对可靠服务器进行了快速测试：

if nc -zw1 google.com 443; then
  echo "we have connectivity"
fi

这会nc在其端口扫描模式下使用netcat（），它-z是一种具有快速超时（最多等待一秒钟）的快速戳（是零I / O模式（用于扫描）-w 1）。它在端口443（HTTPS）上检查Google。

我一直使用HTTPS而不是HTTP来防止捕获门户网站和透明代理，这些门户可以在端口80（HTTP）上对任何主机进行应答。使用端口443的可能性较小，因为可能会出现证书不匹配的情况，但仍然会发生。

如果要证明这一点，则需要验证连接的安全性：

test=google.com
if nc -zw1 $test 443 && echo |openssl s_client -connect $test:443 2>&1 |awk '
  handshake && $1 == "Verification" { if ($2=="OK") exit; exit 1 }
  $1 $2 == "SSLhandshake" { handshake = 1 }'
then
  echo "we have connectivity"
fi

这将检查连接（而不是等待openssl超时），然后进行SSL握手，从而在验证阶段键入密钥。如果验证是“ OK”，它会静默退出（“ true”），否则会出现错误（“ false”）而退出，然后我们报告发现。

我编写了一个脚本，该脚本使用多种方式检查Internet连接（ping，nc和curl），这要归功于Adam Katz，Gilles和Archemar。我希望有人觉得这有用。可以根据自己的喜好对其进行编辑/优化。

检查您的网关，DNS和Internet连接（使用curl，nc和ping）。将其放入文件中，然后使其可执行（通常为sudo chmod +x filename）

#!/bin/bash

GW=`/sbin/ip route | awk '/default/ { print $3 }'`
checkdns=`cat /etc/resolv.conf | awk '/nameserver/ {print $2}' | awk 'NR == 1 {print; exit}'`
checkdomain=google.com

#some functions

function portscan
{
  tput setaf 6; echo "Starting port scan of $checkdomain port 80"; tput sgr0;
  if nc -zw1 $checkdomain  80; then
    tput setaf 2; echo "Port scan good, $checkdomain port 80 available"; tput sgr0;
  else
    echo "Port scan of $checkdomain port 80 failed."
  fi
}

function pingnet
{
  #Google has the most reliable host name. Feel free to change it.
  tput setaf 6; echo "Pinging $checkdomain to check for internet connection." && echo; tput sgr0;
  ping $checkdomain -c 4

  if [ $? -eq 0 ]
    then
      tput setaf 2; echo && echo "$checkdomain pingable. Internet connection is most probably available."&& echo ; tput sgr0;
      #Insert any command you like here
    else
      echo && echo "Could not establish internet connection. Something may be wrong here." >&2
      #Insert any command you like here
#      exit 1
  fi
}

function pingdns
{
  #Grab first DNS server from /etc/resolv.conf
  tput setaf 6; echo "Pinging first DNS server in resolv.conf ($checkdns) to check name resolution" && echo; tput sgr0;
  ping $checkdns -c 4
    if [ $? -eq 0 ]
    then
      tput setaf 6; echo && echo "$checkdns pingable. Proceeding with domain check."; tput sgr0;
      #Insert any command you like here
    else
      echo && echo "Could not establish internet connection to DNS. Something may be wrong here." >&2
      #Insert any command you like here
#     exit 1
  fi
}

function httpreq
{
  tput setaf 6; echo && echo "Checking for HTTP Connectivity"; tput sgr0;
  case "$(curl -s --max-time 2 -I $checkdomain | sed 's/^[^ ]*  *\([0-9]\).*/\1/; 1q')" in
  [23]) tput setaf 2; echo "HTTP connectivity is up"; tput sgr0;;
  5) echo "The web proxy won't let us through";exit 1;;
  *)echo "Something is wrong with HTTP connections. Go check it."; exit 1;;
  esac
#  exit 0
}


#Ping gateway first to verify connectivity with LAN
tput setaf 6; echo "Pinging gateway ($GW) to check for LAN connectivity" && echo; tput sgr0;
if [ "$GW" = "" ]; then
    tput setaf 1;echo "There is no gateway. Probably disconnected..."; tput sgr0;
#    exit 1
fi

ping $GW -c 4

if [ $? -eq 0 ]
then
  tput setaf 6; echo && echo "LAN Gateway pingable. Proceeding with internet connectivity check."; tput sgr0;
  pingdns
  pingnet
  portscan
  httpreq
  exit 0
else
  echo && echo "Something is wrong with LAN (Gateway unreachable)"
  pingdns
  pingnet
  portscan
  httpreq

  #Insert any command you like here
#  exit 1
fi

互联网上有很多IP，一种简便的方法是ping其中一些

 if ping -c 4 google.com ; then OK ; else KO ; fi
 if ping -c 4 facebook.com ; then OK ; else KO ; fi
 if ping -c 4 nsa.gov ; then OK ; else KO ; fi # <- this one might not reply

一个更完整的答案可能是使用 wget

 wget google.com -o google.txt
 if parse google.txt ; then OK ; else KO ; fi

哪里

• parse是您编写的程序，可确保google.txt不是google.com的（太旧）缓存版本

多亏了每个用户和其他网站的贡献，我设法在3天内完成了该脚本。我将免费提供它使用。

当连接断开时，此脚本会自动执行ip地址的更新，并且会持续进行。

#!/bin/bash

# Autor: John Llewelyn
# FB: fb.com/johnwilliam.llewelyn
# Twitter: twitter.com/JWLLEWELYN
# TLF: +584-1491-011-15
# Its use is free.
# Description: Connection Monitor for ADSL modem.
# Requirements:
# Copy this code or save to /home/administrator/ConnectionMonitor.sh
# It requires the installed packages fping beep and cron
# Comment the blacklist pcspkr snd-pcsp in /etc/modprobe.d/blacklist.conf
# Give execute permissions: chmod +x /home/administrator/ConnectionMonitor.sh
# Add this line in crontab -e with root user
# @reboot sleep 120 && /home/administrator/MonitorDeConexion.sh

#################################################################################
# SETTINGS
TEST="8.8.8.8"       # TEST PING
ADAPTER1="enp4s0"    # EXTERNAL ETHERNET ADAPTER

# Report
LOGFILE=/home/administrator/Documentos/ReportInternet.log

# Messages
MESSAGE1="Restoring Connectivity..."
MESSAGE2="Wait a moment please..."
MESSAGE3="No Internet connectivity."
MESSAGE4="Yes, there is Internet connectivity."
#################################################################################

# Time and Date
TODAY=$(date "+%r %d-%m-%Y")

# Show IP Public Address
IPv4ExternalAddr1=$(ip addr list $ADAPTER1 |grep "inet " |cut -d' ' -f6|cut -d/ -f1)
IPv6ExternalAddr1=$(ip addr list $ADAPTER1 |grep "inet6 " |cut -d' ' -f6|cut -d/ -f1)

# Alarm
alarm() {
    beep -f 1500 -l 200;beep -f 1550 -l 200;beep -f 1500 -l 200;beep -f 1550 -l 200;beep -f 1500 -l 200;beep -f 1550 -l 200;beep -f 1500 -l 200;beep -f 1550$
}

# Restoring Connectivity
resolve() {
    clear
    echo "$MESSAGE1"
    sudo ifconfig $ADAPTER1 up;sudo dhclient -r $ADAPTER1;sleep 5;sudo dhclient $ADAPTER1
    echo "$MESSAGE2"
    sleep 120
}

# Execution of work
while true; do
    if [[ "$(fping -I $ADAPTER1 $TEST | grep 'unreachable' )" != "" ]]; then
        alarm
        clear
        echo "================================================================================" >> ${LOGFILE}
        echo "$MESSAGE3 - $TODAY"                                                               >> ${LOGFILE}
        echo "$MESSAGE3 - $TODAY"
        echo "================================================================================" >> ${LOGFILE}
        sleep 10
        resolve
    else
        clear
        echo "================================================================================"   >> ${LOGFILE}
        echo "$MESSAGE4 - $TODAY - IPv4 Addr: $IPv4ExternalAddr1 - IPv6 Addr: $IPv6ExternalAddr1" >> ${LOGFILE}
        echo "$MESSAGE4 - $TODAY - IPv4 Addr: $IPv4ExternalAddr1 - IPv6 Addr: $IPv6ExternalAddr1"
        echo "================================================================================"   >> ${LOGFILE}
        sleep 120
    fi
done

pastebin：https：//pastebin.com/wfSkpgKA