How to test an Internet connection with bash

Question

How can an internet connection be tested without pinging some website  I mean  what if there is a connection but the site is down  Is there a check for a connection with the world

User · Answer

If your local nameserver is down    ping 4 2 2 1   is an easy-to-remember always-up IP  it s actually a nameserver  even

User · Answer

I ve written scripts before that simply use telnet to connect to port 80  then transmit the text   HTTP 1 0 GET  index html   followed by two CR LF sequences   Provided you get back some form of HTTP response  you can generally assume the site is functioning

User · Answer

The top voted answer does not work for MacOS so for those on a mac  I ve successfully tested this   GATEWAY  route -n get default   grep gateway  if   -z   GATEWAY      then     echo error else   ping -q -t 1 -c 1  echo  GATEWAY   cut -d     -f 2   gt   dev null  amp  amp  echo ok    echo error fi   tested on MacOS High Sierra 10 12 6

User · Answer

Execute the following command to check whether a web site is up  and what status message the web server is showing  curl -Is http   www google com   head -1 HTTP 1 1 200 OK Status code    200 OK    means that the request has succeeded and a website is reachable

User · Answer

Without ping     bin bash  wget -q --spider http   google com  if      -eq 0    then     echo  Online  else     echo  Offline  fi   -q   Silence mode  --spider   don t get  just check page availability       shell return code  0   shell  All OK  code  Without wget     bin bash  echo -e  GET http   google com HTTP 1 0 n n    nc google com 80  gt   dev null 2 gt  amp 1  if      -eq 0    then     echo  Online  else     echo  Offline  fi

User · Answer

This works on both MacOSX and Linux      bin bash  ping -q -w1 -c1 google com  amp  gt  dev null  amp  amp  echo online    echo offline

User · Answer

Checking Google s index page is another way to do it      bin bash  WGET   usr bin wget    WGET -q --tries 20 --timeout 10 http   www google com -O  tmp google idx  amp  gt   dev null if     -s  tmp google idx   then     echo  Not Connected     else     echo  Connected     fi

User · Answer

For the fastest result  ping a DNS server  ping -c1  quot 8 8 8 8 quot   amp  gt  quot  dev null quot   if     quot      quot  -ne 0     then     echo  quot offline quot  elif     quot    args     quot  -eq 0     then     echo  quot online quot  fi  Available as a standalone command  linkStatus

User · Answer

The top answer misses the fact that you can have a perfectly stable connection to your default gateway but that does not automatically mean you can actually reach something on the internet  The OP asks how he she can test a connection with the world  So I suggest to alter the top answer by changing the gateway IP to a known IP  x y z w  that is outside your LAN    So the answer would become   ping -q -w 1 -c 1 x y z w  gt   dev null  amp  amp  echo ok    echo error   Also removing the unfavored backticks for command substitution 1    If you just want to make sure you are connected to the world before executing some code you can also use   if ping -q -w 1 -c 1 x y z w  gt   dev null  then       more code fi

User · Answer

This bash script continuously check for Internet and make a beep sound when the Internet is available      bin bash play -n synth 0 3 sine 800 vol 0 75 while   do pingtime   ping -w 1 8 8 8 8   grep ttl  if     pingtime          then     pingtimetwo   ping -w 1 www google com   grep ttl      if     pingtimetwo             then         clear   echo  Offline     else        clear   echo  Online    play -n synth 0 3 sine 800 vol 0 75    fi  else     clear   echo  Online    play -n synth 0 3 sine 800 vol 0 75 fi sleep 1 done

User · Answer

In Bash  using it s network wrapper through  dev  udp tcp  host port  if    gt  dev tcp 8 8 8 8 53  then   echo  Internet available   else   echo  Offline   fi     is the Bash no-op  because you just want to test the connection  but not processing

User · Answer

shortest way  fping 4 2 2 1     4 2 2 1 is alive   i prefer this as it s faster and less verbose output than ping  downside is you will have to install it   you can use any public dns rather than a specific website   fping -q google com  amp  amp  echo  do something because you re connected    -q returns an exit code  so i m just showing an example of running something you re online   to install on mac  brew install fping  on ubuntu  sudo apt-get install fping

User · Answer

make sure your network allow TCP traffic in and out  then you could get back your public facing IP with the following command  curl ifconfig co

User · Answer

Super Thanks to user somedrew for their post here  https   bbs archlinux org viewtopic php id 55485 on 2008-09-20 02 09 48  Looking in  sys class net should be one way  Here s my script to test for a network connection other than the loop back  I use the below in another script that I have for periodically testing if my website is accessible  If it s NOT accessible a popup window alerts me to a problem  The script below prevents me from receiving popup messages every five minutes whenever my laptop is not connected to the network     usr bin bash    Test for network conection for interface in   ls  sys class net    grep -v lo   do   if      cat  sys class net  interface carrier    1     then OnLine 1  fi done if      OnLine    then echo  quot Not Online quot   gt   dev stderr  exit  fi  Note for those new to bash  The final  if  statement tests if NOT     online and exits if this is the case  See man bash and search for  quot Expressions may be combined quot  for more details  P S  I feel ping is not the best thing to use here because it aims to test a connection to a particular host NOT test if there is a connection to a network of any sort  P P S  The Above works on Ubuntu 12 04 The  sys may not exist on some other distros  See below   Modern Linux distributions include a  sys directory as a virtual filesystem  sysfs  comparable to  proc  which is a procfs   which stores and allows modification of the devices connected to the system  whereas many traditional UNIX and Unix-like operating systems use  sys as a symbolic link to the kernel source tree  citation needed  From Wikipedia https   en wikipedia org wiki Filesystem Hierarchy Standard

User · Answer

Pong doesn t mean web service on the server is running  it merely means that server is replying to ICMP echo  I would recommend using curl and check its return value

User · Answer

Ping was designed to do exactly what you re looking to do  However  if the site blocks ICMP echo  then you can always do the telnet to port 80 of some site  wget  or curl

User · Answer

Similarly to  Jesse s answer  this option might be much faster than any solution using ping and perhaps slightly more efficient than  Jesse s answer   find  sys class net  -maxdepth 1 -mindepth 1   -name   lo   -exec sh -c  cat   0  carrier 2 gt  amp 1          grep -q  1    Explenation   This command uses find with -exec to run command on all files not named  lo  in  sys class net   These should be links to directories containing information about the available network interfaces on your machine   The command being ran is an sh command that checks the contents of the file carrier in those directories  The value of  interface carrier has 3 meanings - Quoting      It seems there are three states            carrier not readable  for instance when the interface is disabled in Network Manager       carrier contain  1   when the interface is activated and it is connected to a WiFi network      carrier contain  0   when the interface is activated and it is not connected to a WiFi network       The first option is not taken care of in  Jesse s answer  The sh command striped out is     Note   0     interface cat   0  carrier 2 gt  amp 1   cat is being used to check the contents of carrier and redirect all output to standard output even when it fails because the file is not readable  If grep -q finds  1  among those files it means there is at least 1 interface connected  The exit code of grep -q will be the final exit code   Usage  For example  using this command s exit status  you can use it start a gnubiff in your    xprofile only if you have an internet connection   online         find  sys class net  -maxdepth 1 -mindepth 1   -name   lo   -exec sh -c  cat   0  carrier 2 gt  amp 1  gt   dev null   grep -q  1   amp  amp  exit 0          online  amp  amp  gnubiff --systemtray --noconfigure  amp    Reference   Help testing special file in  sys class net  find -exec a shell function

User · Answer

Ping your default gateway      bin bash ping -q -w 1 -c 1  ip r   grep default   cut -d     -f 3   gt   dev null  amp  amp  echo ok    echo error

User · Answer

If your goal is to actually check for Internet access  many of the existing answers to this question are flawed  A few things you should be aware of    It s possible for your computer to be connected to a network without that network having internet access It s possible for a server to be down without the entire internet being inaccessible It s possible for a captive portal to return an HTTP response for an arbitrary URL even if you don t have internet access   With that in mind  I believe the best strategy is to contact several sites over an HTTPS connection and return true if any of those sites responds   For example   connected to internet       test urls      https   www google com      https   www microsoft com      https   www cloudflare com           processes  0    pids       for test url in  test urls  do     curl --silent --head   test url   gt   dev null  amp      pids   pids         processes     processes   1     done    while    processes -gt 0    do     for pid in  pids  do       if   ps   grep      blank     pid   blank      gt   dev null  then           Process no longer running         processes     processes - 1           pids   echo   pids    sed --regexp-extended  s       pid        g            if wait  pid  then             Success  We have a connection to at least one public site  so the             internet is up  Ignore other exit statuses            kill -TERM  pids  gt   dev null 2 gt  amp 1    true           wait  pids           return 0         fi       fi     done       wait -n  pids   Better than sleep  but not supported on all systems     sleep 0 1   done    return 1     Usage   if connected to internet  then   echo  Connected to internet  else   echo  No internet connection  fi   Some notes about this approach    It is robust against all the false positives and negatives I outlined above The requests all happen in parallel to maximize speed It will return false if you technically have internet access but DNS is non-functional or your network settings are otherwise messed up  which I think is a reasonable thing to do in most cases

[bash] How to test an Internet connection with bash?

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