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?
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 > /dev/null 2>&1
if [ $? -eq 0 ]; then
echo "Online"
else
echo "Offline"
fi
Ping your default gateway:
#!/bin/bash
ping -q -w 1 -c 1 `ip r | grep default | cut -d ' ' -f 3` > /dev/null && echo ok || echo error
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 "Not Online" > /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 "Expressions may be combined" 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
This works on both MacOSX and Linux:
#!/bin/bash
ping -q -c1 google.com &>/dev/null && echo online || echo offline
In Bash, using it's network wrapper through /dev/{udp,tcp}/host/port:
if : >/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.)
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 > /dev/null && 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 > /dev/null; then
# more code
fi
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.
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
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.
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 $GATEWAY | cut -d ':' -f 2` > /dev/null && echo ok || echo error
fi
tested on MacOS High Sierra 10.12.6
If your local nameserver is down,
ping 4.2.2.1
is an easy-to-remember always-up IP (it's actually a nameserver, even).
This bash script continuously check for Internet and make a beep sound when the Internet is available.
#!/bin/bash
play -n synth 0.3 sine 800 vol 0.75
while :
do
pingtime=$(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
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>&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>&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>&1 > /dev/null | grep -q "1" && exit 0' {} \;
}
online && gnubiff --systemtray --noconfigure &
Reference
Help testing special file in /sys/class/net/
find -exec a shell function?
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 && 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
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.
Checking Google's index page is another way to do it:
#!/bin/bash
WGET="/usr/bin/wget"
$WGET -q --tries=20 --timeout=10 http://www.google.com -O /tmp/google.idx &> /dev/null
if [ ! -s /tmp/google.idx ]
then
echo "Not Connected..!"
else
echo "Connected..!"
fi
For the fastest result, ping a DNS server:
ping -c1 "8.8.8.8" &>"/dev/null"
if [[ "${?}" -ne 0 ]]; then
echo "offline"
elif [[ "${#args[#]}" -eq 0 ]]; then
echo "online"
fi
Available as a standalone command: linkStatus
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.
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" > /dev/null &
pids="$pids $!"
processes=$(($processes + 1))
done
while [ $processes -gt 0 ]; do
for pid in $pids; do
if ! ps | grep "^[[:blank:]]*$pid[[:blank:]]" > /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 > /dev/null 2>&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
If you want to handle captive portals, you can do this oneliner:
if [[ $(curl -s -D - http://www.gstatic.com/generate_204 2>/dev/null | head -1 | cut -d' ' -f 2) == "204" ]]; then
echo 'online'
else
echo 'offline'
fi
Or if you want something more readable that can differentiate captive portals from lack of signal:
function is_online() {
# Test signal
local response
response=$(curl --silent --dump-header - http://www.gstatic.com/generate_204 2> /dev/null)
if (($? != 0)); then return 2; fi
# Test captive portal
local status=$(echo $response | head -1 | cut -d' ' -f 2)
((status == "204"))
}
is_online && echo online || echo offline
Related
Being a noob, I can't comment, so posting a question to expand on the answers for this thread; How to test an Internet connection with bash?
for Mac users.
The -w1 or -w 1 option specified in the answers does not work on Mac
However, -W1 or -W 1 does work. It is a case sensitivity issue for the Mac rather than an invalid/unavailable option.
On Mac: I assume you need a timeout? What's wrong with using the -t option (timeout) ?
A script for this, adapted from your link:
checkInternet () {
error=$(ping -q -t1 -c1 "8.8.8.8" 2>&1 >"/dev/null" || true)
if [ "${error}" != "" ]; then
echo "No internet" >&2
exit 1
fi
echo "Internet" >&2
}
checkInternet
Is there an easy way to check Internet connectivity from console? I am trying to play around in a shell script. One idea I seem is to wget --spider http://www.google.com/ and check the HTTP response code to interpret if the Internet connection is working fine.
This is what I am trying:
#!/bin/bash
# Sending the output of the wget in a variable and not what wget fetches
RESULT=`wget --spider http://google.com 2>&1`
FLAG=0
# Traverse the string considering it as an array of words
for x in $RESULT; do
if [ "$x" = '200' ]; then
FLAG=1 # This means all good
fi
done
Is there any way to accomplish this?
You can do it with ping or curl commands. Check man for more.
I am using this for myself and kinda works for me! It checks the connection from a reliable website like google and if it gets 200 status as the response, you probably have internet.
if curl -s --head --request GET www.google.com | grep "200 OK" > /dev/null ; then
echo "Internet is present"
else
echo "Internet isn't present"
fi
On one line, thanks #PS
if ping -c1 8.8.8.8 &>/dev/null ;then echo Working ;else echo Down ;fi
An option that does not use the internet to see if it is available is to check for a default route in your routing tables. The routing daemon will remove your default route when the internet is not available and add it back when it is.
netstat -nrf inet | grep -q ^default && \
echo internet is up || \
echo internet is down
To check if a website is up, you can use netcat to see if it is listening on port 80. This helps with sites that refuse head requests with '405 Method Not Allowed'.
nc -zw2 www.example.com 80 &>/dev/null && \
echo website is up || \
echo website is down
Please try this code.
#!/bin/bash
wget -q --spider http://google.com
if [ $? -eq 0 ]; then
echo "Internet connection is OK"
else
echo "Internet connection is FAILED"
fi
A bit more compact variant of #carlos-abraham answer. You can have curl to output just the http response code and make a decision with it
# 200 if everything is ok
http_code=$(curl -s --head -m 5 -w %{http_code} --output /dev/null www.google.com)
if [ "$http_code" -eq 200 ]; then
echo "success"
else
# write error to stderr
echo "http request failed: $http_code" >&2
exit 1
fi
-m 5: wait 5 seconds for the whole operation
--output /dev/null: suppress html site response
-w %{http_code}: write to stdout the http response code.
A bit more elaborated script to check connectivity and http response
#url="mmm.elgoog.moc"
url="www.google.com"
max_wait=5
(ping -w $max_wait -q -c 1 "$url" > /dev/null 2>&1 )
response_code=$?
if [ "$response_code" -eq 0 ]; then
# 200 if everything is ok
response_code=$(curl -s --head -m $max_wait -w %{http_code} --output /dev/null "$url")
fi
case "$response_code" in
1)
echo "Connectivity failed. Host down?" >&2
exit $response_code
;;
2)
echo "Unknown host or other problem. DNS problem?" >&2
exit $response_code
;;
200)
echo "success"
exit 0
;;
*)
echo "Failed to get a response: $response_code" >&2
exit 1
esac
#!/bin/bash
ip route add 10.105.8.100 via 192.168.1.100
date
cat /home/xxx/Documents/list.txt | while read output
do
ping="ping -c 3 -w 3 -q 'output'"
if $ping | grep -E "min/avg/max/mdev" > /dev/null; then
echo 'connection is ok'
else
echo "router $output is down"
then
cat /home/xxx/Documents/roots.txt | while read outputs
do
cd /home/xxx/Documents/routers
php rebootRouter.php "outputs" admin admin
done
fi
done
The other documents are:
lists.txt
10.105.8.100
roots.txt
192.168.1.100
when i run the script, the result is a reboot of the router am trying to ping. It doesn't ping.
Is there a problem with the bash script.??
If your files only contain a single line, there's no need for the while-loop, just use read:
read -r router_addr < /home/xxx/Documents/list.txt
# the grep is unnecessary, the return-code of the ping will be non-zero if the host is down
if ping -c 3 -w 3 -q "$router_addr" &> /dev/null; then
echo "connection to $router_addr is ok"
else
echo "router $router_addr is down"
read -r outputs < /home/xxx/Documents/roots.txt
cd /home/xxx/Documents/routers
php rebootRouter.php "$outputs" admin admin
fi
If your files contain multiple lines, you should redirect the file from the right-side of the while-loop:
while read -r output; do
...
done < /foo/bar/baz
Also make sure your files contain a newline at the end, or use the following pattern in your while-loops:
while read -r output || [[ -n $output ]]; do
...
done < /foo/bar/baz
where || [[ -n $output ]] is true even if the file doesn't end in a newline.
Note that the way you're checking for your routers status is somewhat brittle as even a single missed ping will force it to reboot (for example the checking computer returns from a sleep-state just as the script is running, the ping fails as the network is still down but the admin script succeeds as the network just comes up at that time).
I have a bash function:
resolv(){
for name in $*; do
test 1 -eq $(ping -c 1 -q "$name"|grep '1 packet transmitted'|wc -l) && echo ok || echo fail
done
}
But if I pass a name that is not defined it returns, always:
ping: unknown host name.that.do.not.resolv
fail
How can I solve this?
You could try getent which follows the /etc/nsswitch.conf config:
> getent hosts my_laptop
127.0.0.1 localhost my_laptop
> getent hosts www.google.com
2607:f8b0:400b:80a::1014 www.google.com
> getent hosts name.that.do.not.resolv
>
Sticking with the assumption you need to use ping (because, for example, of the broken^H^H^Hconfused dns resolution in OSX):
Note that your grep wasn't portable - some pings say "packet" and others say "packets"... within the scope of the ping's I had available, ^PING works though.
For your specific question, you wanted to suppress the error output - so just redirect stderr to /dev/null - if it's sh/bash/similar that'd just be 2>/dev/null
Also added -t1 to reduce the amount of time we might spend on a ping fail/lookup fail...might need to tune to suit.
Broke up the test && || into something more readable (and with more obvious logic direction) since we arent really constrained to a oneliner. :)
#!/bin/sh
resolv(){
for name in $*; do
count=$(ping -c 1 -q -t1 "$name" 2>/dev/null |grep '^PING'|wc -l)
if [ 1 -eq "$count" ]
then
echo ok
else
echo fail
fi
done
}
resolv google.com
resolv icantclick.org
resolv www.yahoo.com
resolv gofish
using this script I am trying to detect if there is a network link. I am failing in putting multiple commands in one line (ethtool...). What to do?
#!/bin/bash
COMMAND="( /sbin/ethtool eth0 ) | ( /bin/grep \"Link detected: yes\" ) | ( wc -l )"
ONLINE=eval $COMMAND
if $ONLINE; then
echo "Online"
else
echo "Not online"
fi
You simply need
if /sbin/ethtool eth0 | grep -q "Link detected: yes"; then
echo "Online"
else
echo "Not online"
fi
Also if you want to encapsulate checking, simply use a function:
function check_eth {
set -o pipefail # optional.
/sbin/ethtool "$1" | grep -q "Link detected: yes"
}
if check_eth eth0; then
echo "Online"
else
echo "Not online"
fi
How it works: if simply interprets a command in front of it and check if the return value of $? is 0. grep returns 0 when it finds a match on its search. And so because of this you don't need to use wc and compare its output to 1.
It appears your script question has been answered. Under Linux I would implement this by reading sysfs directly.
function ifup {
if [[ ! -d /sys/class/net/${1} ]]; then
printf 'No such interface: %s\n' "$1" >&2
return 1
else
[[ $(</sys/class/net/${1}/operstate) == up ]]
fi
}
if ifup enp7s0; then
echo Online
else
echo 'Not online'
fi
My second choice would probably be ip link.
# Returns true if iface exists and is up, otherwise false.
function ifup {
typeset output
output=$(ip link show "$1" up) && [[ -n $output ]]
}
...
At least at my machine (Debian 7.5) only root is allowed to determine link status with ethtool and it is not installed in all distributions.
I can think of three alternatives to ethtool to determine network link status:
ifconfig eth0
ip link show (you have to grep for your interface and "state UP" or "state DOWN")
send one ping to some known online host (could also be given as parameter) in your network (ping -c 1 -w 1 ip_address &> /dev/null, -c specifies the number of packets to send and -w is the timeout in seconds)
Looking at your question can you use /sbin/ifconfig eth0 and check if it has inet or inet6 address, or you can also check for the line UP BROADCAST RUNNING MULTICAST. If the network is down the line will be UP BROADCAST MULTICAST
You can check the man page of ifconfig for more information.
Different functions for different purposes:
## (1) check if there is any interface UP
## loopback interface (lo) is excluded
_isInterfaceUp(){
ip link|grep -v '[0-9]: lo:' 2>/dev/null|grep -l '^[0-9].* UP ' >/dev/null 2>&1
}
## (2) check if there is a valid default gateway in the routing table
## note: routes via non-active interfaces are excluded
_isNetworkUp(){
ip route|grep '^default via ' 2>/dev/null|grep -lv 'linkdown' >/dev/null 2>&1
}
## (3) check if Internet is connected properly
_isInternetConnected(){
if ! ping -c 4 8.8.8.8 >/dev/null 2>&1; then
## ping might be firewalled, so check a webpage then
curl -Hfs www.google.com >/dev/null 2>&1 || return 1
fi
return 0
}
In real practices, I do not use the function (1), because it rarely useful simply to check if there is an interface UP. However I do use funtions (2) + (3):
The function (2) _isNetworkUp is called periodically in a script just to show whether my computer is networked
The function (3) _isInternetConnected is called in a script before doing something with internet, like sync computer time and check email. Because the function (3) costs more time and resources than function (2), so it is not suitable for periodically usage of short time interval. curl is more costly than ping; so ping first, then curl later.
(sorry if my English is lousy).
Examples:
## if Internet is connected, then sync time
## with world time server
if _isInternetConnected; then
sudo ntpdate pool.ntp.org
sudo hwclock --systohc --utc
fi
Explanations:
grep -l : grep stops immediate after 1st found.
grep -v : grep exclusively.
ping -c 4: ping only 4 times.