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I'm trying to do a custom dockerfile with jenkins on it. I would to wait until port 8080 is open instead of doing an ugly 'sleep 60' with netcat but I'm not very confident with bash scripts and netcat.
Here is an example of what i'm trying to do:
#!/bin/bash
opened=0
while [ "$opened" == "0" ]; do
echo "Waiting jenkins to launch on 8080..."
nc -vz localhost 8080
done
echo "Jenkins launched"
You can't set netcat to wait until some port is open, so you have to add part for waiting before next check is made. Try this:
#!/bin/bash
echo "Waiting jenkins to launch on 8080..."
while ! nc -z localhost 8080; do
sleep 0.1 # wait for 1/10 of the second before check again
done
echo "Jenkins launched"
I suggest the following one liners:
## netcat version:
timeout 22 sh -c 'until nc -z $0 $1; do sleep 1; done' stackoverflow.com 443
## pure bash version:
timeout 22 bash -c 'until printf "" 2>>/dev/null >>/dev/tcp/$0/$1; do sleep 1; done' stackoverflow.com 443
Both commands exit as soon as connection is established, trying every second for up to 22 seconds.
Note that thanks to timeout command exit code is 0 when port is accessible otherwise 124 (if no connection established within given time).
As suggested here, you could also do the following if you don't have nc installed but just bash and coreutils:
#!/bin/bash
echo "Waiting jenkins to launch on 8080..."
while ! timeout 1 bash -c "echo > /dev/tcp/localhost/8080"; do
sleep 1
done
echo "Jenkins launched"
I have found this a common enough problem to write a utility to wait for a port to open, with an optional timeout:
# without timeout
wait-port localhost:8080
# timeout after a minute
wait-port -t 60000 localhost:8080
It's open source and available at github.com/dwmkerr/wait-port. Hopefully others will find it useful!
To expand on user987339's answer, here's how to easily wait for a port in your terminal:
waitport function
Add this function to your ~/.bashrc setup file:
waitport() {
while ! nc -z localhost $1 ; do sleep 1 ; done
}
Log out then back in to load ~/.bashrc. Then, run this command to verify that port 3000 has a server listening to it:
$ waitport 3000
Connection to localhost port 3000 [tcp/hbci] succeeded!
This has been validated on macOS. It might not work on Fedora/CentOS, as they lack the -z option for netcat.
To add onto the excellent answers above, if this is something used very often it may be worthwhile to use tooling for that purpose. I wrote and use uup all the time for this use case.
In your example, the command to run would be:
uup localhost:8080 -r
providing an output like:
Here is a for-loop example that has a timeout, so it tries e.g. for 10 times, with exponential backoff (2,4,8,16 seconds etc), but finally gives up. Netcat has also 1 second timeout.
for EXPONENTIAL_BACKOFF in {1..10}; do
nc -w 1 -z db.local 3306 && break;
DELAY=$((2**$EXPONENTIAL_BACKOFF))
echo "db not yet available, sleeping for $DELAY seconds"
sleep $DELAY
done
The output is:
db not yet available, sleeping for 2 seconds
db not yet available, sleeping for 4 seconds
db not yet available, sleeping for 8 seconds
db not yet available, sleeping for 16 seconds
I use this script to check the port before running tests on CI.
#!/bin/bash
for _ in `seq 1 20`; do
echo -n .
if nc -z localhost $1; then
exit 0
fi
sleep 0.5
done
exit 1
$ bin/wait-port 3306
Here is my one-line Bash solution (with netcat) that waits for 10 sec for a TCP connection, and give you feedback whether succeeded or not and while is waiting, and return an exit 0 code if the port is open, otherwise 1:
bash -c 'echo -n "Waiting port 8080 .."; for _ in `seq 1 40`; do echo -n .; sleep 0.25; nc -z localhost 8080 && echo " Open." && exit ; done; echo " Timeout!" >&2; exit 1'
You can replace the hardcoded port 8080 by $1 and remove the bash -c if the snippet is saved in a script file wait-port than then is called within a console with: wait-port 8080.
This is a recording of 3 terminals, two waiting until a port is opened and the other terminals open one of the port, so while one of the wait succeed, the other timed-out:
Although the line has many instructions not one, it may be useful if you need to execute the wait "remotely" in a host where you cannot store the script first, e.g. in a Docker container.
I used this to wait for a couple of ports to be open, without netcat:
while (! (: </dev/tcp/localhost/27017) &> /dev/null || ! (: </dev/tcp/localhost/9200) &> /dev/null); do
sleep 2;
done
Change localhost and the ports as needed.
For those people who are having trouble with nc: invalid option -- 'z'
I was trying to set this up in a docker image. Surprisingly, there was no option of -z in nc in that image.
Image was - Linux elasticsearch 4.4.0-101-generic #124~14.04.1-Ubuntu SMP Fri Nov 10 19:05:36 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
I used the following loop to wait until the port was opened.
#!/bin/bash
echo "Waiting elastic search to launch on 9200..."
open=0;
while [ $open -eq 0 ]
do
check_port=`nc -v -w 1 -i 1 127.0.0.1 9200 &> /dev/stdout`
echo $check_port
if [[ "$check_port" == *"Connected to"* ]]
then
break
fi
sleep 1
done
echo "Elastic Search launched"
Following is the one-liner of the above script:
open=0;while [ $open -eq 0 ]; do check_port=`nc -v -w 1 -i 1 127.0.0.1 9200 &> /dev/stdout`; echo $check_port; if [[ "$check_port" == *"Connected to"* ]]; then break; fi; sleep 1; done
I have written a utility to wait for a port to open, it can also check MySQL, PostgreSQL, Redis and etc availability.
# Checking TCP port
wait4x tcp localhost:8080
# Checking TCP port with specific timeout (5 Minutes)
wait4x tcp localhost:8080 -t 5m
It's open source and available at https://github.com/atkrad/wait4x. Hopefully others will find it useful!
If you are looking for a docker-run-one-liner, check out my Docker image based on the netcat loop:
$ docker run --rm igops/wait-for-port HOST PORT
E.g.,
$ docker run --rm igops/wait-for-port 172.17.0.1 80
will query 172.17.0.1:80 each 0.1s and exit when the connection is established:
Waiting for 172.17.0.1:80...
OK
Waiting for another container to response:
$ docker network create my-bridge
$ docker run --rm -d --net my-bridge --net-alias my-mongo mongo
$ docker run --rm --net my-bridge igops/wait-for-port my-mongo 27017
$ echo "Mongo is up at this point, do some useful stuff here"
Waiting for some service on the docker host:
$ docker run --rm --add-host="docker-host:host-gateway" igops/wait-for-port docker-host 22
$ echo "SSH server is running"
Waiting for another container which published some port:
$ docker run --rm -d -p 27017:27107 mongo
$ docker run --rm --add-host="docker-host:host-gateway" igops/wait-for-port docker-host 27017
$ echo "Mongo is up"
Read more
Why does the following netcat command not time out if the attempt to connect takes longer than 3 seconds (ie: when the port isn't open)? I assumed that the -w flag would be what I needed. OS is OSX 10.9.
nc -v -z -w 3 127.0.0.1 5050
Assuming that worked, I planned to implement like this (unsure if this will work, total bash noob)
nc -v -z -w 3 127.0.0.1 5050 | /dev/null && echo "Online" || echo "Offline"
You need to redirect to /dev/null, not pipe to it. Try the following:
nc -v -z -w 3 127.0.0.1 5050 &> /dev/null && echo "Online" || echo "Offline"
On my machine, port 5050 isn't open, and I get the following:
$ nc -v -z -w 3 localhost 5050 &> /dev/null && echo "Online" || echo "Offline"
Offline
Since Mac OS X 10.8.x, nc has used the -G option to set the timeout for initiating a connection. This is separate from the -w option, which sets the timeout for a connection that has been made but has gone idle.
If you are trying to use nc for port scanning, i.e. nc -v -z 10.0.1.1 1-1023, it will spend over a minute trying to connect to each non-responding port unless you add a -G timeout value:
nc -v -z -G 1 10.0.1.1 1-1023
That's one second per port scanned — much more useful.
Nc: nc is usually installed already , however on some systems such as Mac OS X, the command hangs on unreachable systems without the -G option. If that does not work use the Workaround.
nc -v -z -w 3 127.0.0.1 22 &> /dev/null && echo "Online" || echo "Offline"
Mac OSX:
nc -z -G 3 127.0.0.1 22 &> /dev/null && echo "Online" || echo "Offline"
Alternative workaround option:
bash -c '(sleep 3; kill $$) & exec nc -z 127.0.0.1 22' &> /dev/null
echo $?
0
bash -c '(sleep 3; kill $$) & exec nc -z 1.2.3.4 22' &> /dev/null
echo $?
143
(examples illustrate connecting to port 22 ssh over a good and bad host example, use the $? to determine if it reached the host with the sleep time of 3 seconds)
Alternatively For Mac Users (mainly) etc, you can use the command in the script like so :
# -- use NMAP, if not avail. go with nc --
if command -v nmap | grep -iq nmap ; then
nmap ${ip} -PN -p ${ssh_port} | grep -iq "open"
res=$?
elif command -v nc | grep -iq nc ; then
# -- run command if fails to complete in 3 secs assume host unreachable --
( nc -z ${ip} ${ssh_port} ) & pid=$!
( sleep 3 && kill -HUP $pid ) 2>/dev/null & watcher=$!
if wait $pid 2>/dev/null; then
pkill -HUP -P $watcher
wait $watcher
# -- command finished (we have connection) --
res=0
else
# -- command failed (no connection) --
res=1
fi
else
echo "Error: You must have NC or NMAP installed"
fi
if [[ ${res} -lt 1 ]] ;then
success=1
echo "testing => $ip SUCCESS connection over port ${ssh_port}"
break;
else
echo "testing => $ip FAILED connection over port ${ssh_port}"
fi
There is an old bug report about this on debian (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=97583) and still having the same behavior in Debian GNU/Linux 7.7 (wheezy)
I found a "solution" to this: installing the openbsd version of nc:
apt-get install netcat-openbsd
On Mac OS X (10.14.6) the -w 3 parameter is somehow ignored.
The workaround I found is: timeout 3 nc -vz 10.18.50.134 23
I'm looking for a quick and simple method for properly testing if a given TCP port is open on a remote server, from inside a Shell script.
I've managed to do it with the telnet command, and it works fine when the port is opened, but it doesn't seem to timeout when it's not and just hangs there...
Here's a sample:
l_TELNET=`echo "quit" | telnet $SERVER $PORT | grep "Escape character is"`
if [ "$?" -ne 0 ]; then
echo "Connection to $SERVER on port $PORT failed"
exit 1
else
echo "Connection to $SERVER on port $PORT succeeded"
exit 0
fi
I either need a better way, or a way to force telnet to timeout if it doesn't connect in under 8 seconds for example, and return something I can catch in Shell (return code, or string in stdout).
I know of the Perl method, which uses the IO::Socket::INET module and wrote a successful script that tests a port, but would rather like to avoid using Perl if possible.
Note: This is what my server is running (where I need to run this from)
SunOS 5.10 Generic_139556-08 i86pc i386 i86pc
As pointed by B. Rhodes, nc (netcat) will do the job. A more compact way to use it:
nc -z <host> <port>
That way nc will only check if the port is open, exiting with 0 on success, 1 on failure.
For a quick interactive check (with a 5 seconds timeout):
nc -z -v -w5 <host> <port>
It's easy enough to do with the -z and -w TIMEOUT options to nc, but not all systems have nc installed. If you have a recent enough version of bash, this will work:
# Connection successful:
$ timeout 1 bash -c 'cat < /dev/null > /dev/tcp/google.com/80'
$ echo $?
0
# Connection failure prior to the timeout
$ timeout 1 bash -c 'cat < /dev/null > /dev/tcp/sfsfdfdff.com/80'
bash: sfsfdfdff.com: Name or service not known
bash: /dev/tcp/sfsfdfdff.com/80: Invalid argument
$ echo $?
1
# Connection not established by the timeout
$ timeout 1 bash -c 'cat < /dev/null > /dev/tcp/google.com/81'
$ echo $?
124
What's happening here is that timeout will run the subcommand and kill it if it doesn't exit within the specified timeout (1 second in the above example). In this case bash is the subcommand and uses its special /dev/tcp handling to try and open a connection to the server and port specified. If bash can open the connection within the timeout, cat will just close it immediately (since it's reading from /dev/null) and exit with a status code of 0 which will propagate through bash and then timeout. If bash gets a connection failure prior to the specified timeout, then bash will exit with an exit code of 1 which timeout will also return. And if bash isn't able to establish a connection and the specified timeout expires, then timeout will kill bash and exit with a status of 124.
TOC:
Using bash and timeout
Command
Examples
Using nc
Command
RHEL 6 (nc-1.84)
Installation
Examples
RHEL 7 (nmap-ncat-6.40)
Installation
Examples
Remarks
Using bash and timeout:
Note that timeout should be present with RHEL 6+, or is alternatively found in GNU coreutils 8.22. On MacOS, install it using brew install coreutils and use it as gtimeout.
Command:
$ timeout $TIMEOUT_SECONDS bash -c "</dev/tcp/${HOST}/${PORT}"; echo $?
If parametrizing the host and port, be sure to specify them as ${HOST} and ${PORT} as is above. Do not specify them merely as $HOST and $PORT, i.e. without the braces; it won't work in this case.
Example:
Success:
$ timeout 2 bash -c "</dev/tcp/canyouseeme.org/80"; echo $?
0
Failure:
$ timeout 2 bash -c "</dev/tcp/canyouseeme.org/81"; echo $?
124
If you must preserve the exit status of bash,
$ timeout --preserve-status 2 bash -c "</dev/tcp/canyouseeme.org/81"; echo $?
143
Using nc:
Note that a backward incompatible version of nc gets installed on RHEL 7.
Command:
Note that the command below is unique in that it is identical for both RHEL 6 and 7. It's just the installation and output that are different.
$ nc -w $TIMEOUT_SECONDS -v $HOST $PORT </dev/null; echo $?
RHEL 6 (nc-1.84):
Installation:
$ sudo yum install nc
Examples:
Success:
$ nc -w 2 -v canyouseeme.org 80 </dev/null; echo $?
Connection to canyouseeme.org 80 port [tcp/http] succeeded!
0
Failure:
$ nc -w 2 -v canyouseeme.org 81 </dev/null; echo $?
nc: connect to canyouseeme.org port 81 (tcp) timed out: Operation now in progress
1
If the hostname maps to multiple IPs, the above failing command will cycle through many or all of them. For example:
$ nc -w 2 -v microsoft.com 81 </dev/null; echo $?
nc: connect to microsoft.com port 81 (tcp) timed out: Operation now in progress
nc: connect to microsoft.com port 81 (tcp) timed out: Operation now in progress
nc: connect to microsoft.com port 81 (tcp) timed out: Operation now in progress
nc: connect to microsoft.com port 81 (tcp) timed out: Operation now in progress
nc: connect to microsoft.com port 81 (tcp) timed out: Operation now in progress
1
RHEL 7 (nmap-ncat-6.40):
Installation:
$ sudo yum install nmap-ncat
Examples:
Success:
$ nc -w 2 -v canyouseeme.org 80 </dev/null; echo $?
Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Connected to 52.202.215.126:80.
Ncat: 0 bytes sent, 0 bytes received in 0.22 seconds.
0
Failure:
$ nc -w 2 -v canyouseeme.org 81 </dev/null; echo $?
Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Connection timed out.
1
If the hostname maps to multiple IPs, the above failing command will cycle through many or all of them. For example:
$ nc -w 2 -v microsoft.com 81 </dev/null; echo $?
Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Connection to 104.43.195.251 failed: Connection timed out.
Ncat: Trying next address...
Ncat: Connection to 23.100.122.175 failed: Connection timed out.
Ncat: Trying next address...
Ncat: Connection to 23.96.52.53 failed: Connection timed out.
Ncat: Trying next address...
Ncat: Connection to 191.239.213.197 failed: Connection timed out.
Ncat: Trying next address...
Ncat: Connection timed out.
1
Remarks:
The -v (--verbose) argument and the echo $? command are of course for illustration only.
With netcat you can check whether a port is open like this:
nc my.example.com 80 < /dev/null
The return value of nc will be success if the TCP port was opened, and failure (typically the return code 1) if it could not make the TCP connection.
Some versions of nc will hang when you try this, because they do not close the sending half of their socket even after receiving the end-of-file from /dev/null. On my own Ubuntu laptop (18.04), the netcat-openbsd version of netcat that I have installed offers a workaround: the -N option is necessary to get an immediate result:
nc -N my.example.com 80 < /dev/null
In Bash using pseudo-device files for TCP/UDP connections is straight forward. Here is the script:
#!/usr/bin/env bash
SERVER=example.com
PORT=80
</dev/tcp/$SERVER/$PORT
if [ "$?" -ne 0 ]; then
echo "Connection to $SERVER on port $PORT failed"
exit 1
else
echo "Connection to $SERVER on port $PORT succeeded"
exit 0
fi
Testing:
$ ./test.sh
Connection to example.com on port 80 succeeded
Here is one-liner (Bash syntax):
</dev/tcp/localhost/11211 && echo Port open. || echo Port closed.
Note that some servers can be firewall protected from SYN flood attacks, so you may experience a TCP connection timeout (~75secs). To workaround the timeout issue, try:
timeout 1 bash -c "</dev/tcp/stackoverflow.com/81" && echo Port open. || echo Port closed.
See: How to decrease TCP connect() system call timeout?
I needed a more flexible solution for working on multiple git repositories so I wrote the following sh code based on 1 and 2. You can use your server address instead of gitlab.com and your port in replace of 22.
SERVER=gitlab.com
PORT=22
nc -z -v -w5 $SERVER $PORT
result1=$?
#Do whatever you want
if [ "$result1" != 0 ]; then
echo 'port 22 is closed'
else
echo 'port 22 is open'
fi
check ports using bash
Example
$ ./test_port_bash.sh 192.168.7.7 22
the port 22 is open
Code
HOST=$1
PORT=$2
exec 3> /dev/tcp/${HOST}/${PORT}
if [ $? -eq 0 ];then echo "the port $2 is open";else echo "the port $2 is closed";fi
If you're using ksh or bash they both support IO redirection to/from a socket using the /dev/tcp/IP/PORT construct. In this Korn shell example I am redirecting no-op's (:) std-in from a socket:
W$ python -m SimpleHTTPServer &
[1] 16833
Serving HTTP on 0.0.0.0 port 8000 ...
W$ : </dev/tcp/127.0.0.1/8000
The shell prints an error if the socket is not open:
W$ : </dev/tcp/127.0.0.1/8001
ksh: /dev/tcp/127.0.0.1/8001: cannot open [Connection refused]
You can therefore use this as the test in an if condition:
SERVER=127.0.0.1 PORT=8000
if (: < /dev/tcp/$SERVER/$PORT) 2>/dev/null
then
print succeeded
else
print failed
fi
The no-op is in a subshell so I can throw std-err away if the std-in redirection fails.
I often use /dev/tcp for checking the availability of a resource over HTTP:
W$ print arghhh > grr.html
W$ python -m SimpleHTTPServer &
[1] 16863
Serving HTTP on 0.0.0.0 port 8000 ...
W$ (print -u9 'GET /grr.html HTTP/1.0\n';cat <&9) 9<>/dev/tcp/127.0.0.1/8000
HTTP/1.0 200 OK
Server: SimpleHTTP/0.6 Python/2.6.1
Date: Thu, 14 Feb 2013 12:56:29 GMT
Content-type: text/html
Content-Length: 7
Last-Modified: Thu, 14 Feb 2013 12:55:44 GMT
arghhh
W$
This one-liner opens file descriptor 9 for reading from and writing to the socket, prints the HTTP GET to the socket and uses cat to read from the socket.
While an old question, I've just dealt with a variant of it, but none of the solutions here were applicable, so I found another, and am adding it for posterity. Yes, I know the OP said they were aware of this option and it didn't suit them, but for anyone following afterwards it might prove useful.
In my case, I want to test for the availability of a local apt-cacher-ng service from a docker build. That means absolutely nothing can be installed prior to the test. No nc, nmap, expect, telnet or python. perl however is present, along with the core libraries, so I used this:
perl -MIO::Socket::INET -e 'exit(! defined( IO::Socket::INET->new("172.17.42.1:3142")))'
In some cases where tools like curl, telnet, nc o nmap are unavailable you still have a chance with wget
if [[ $(wget -q -t 1 --spider --dns-timeout 3 --connect-timeout 10 host:port; echo $?) -eq 0 ]]; then echo "OK"; else echo "FAIL"; fi
If you want to use nc but don't have a version that support -z, try using --send-only:
nc --send-only <IP> <PORT> </dev/null
and with timeout:
nc -w 1 --send-only <IP> <PORT> </dev/null
and without DNS lookup if it's an IP:
nc -n -w 1 --send-only <IP> <PORT> </dev/null
It returns the codes as the -z based on if it can connect or not.
Building on the most highly voted answer, here is a function to wait for two ports to be open, with a timeout as well. Note the two ports that mus be open, 8890 and 1111, as well as the max_attempts (1 per second).
function wait_for_server_to_boot()
{
echo "Waiting for server to boot up..."
attempts=0
max_attempts=30
while ( nc 127.0.0.1 8890 < /dev/null || nc 127.0.0.1 1111 < /dev/null ) && [[ $attempts < $max_attempts ]] ; do
attempts=$((attempts+1))
sleep 1;
echo "waiting... (${attempts}/${max_attempts})"
done
}
I needed short script which was run in cron and hasn't output. I solve my trouble using nmap
open=`nmap -p $PORT $SERVER | grep "$PORT" | grep open`
if [ -z "$open" ]; then
echo "Connection to $SERVER on port $PORT failed"
exit 1
else
echo "Connection to $SERVER on port $PORT succeeded"
exit 0
fi
To run it You should install nmap because it is not default installed package.
I'm guessing that it's too late for an answer, and this might not be a good one, but here you go...
What about putting it inside of a while loop with a timer on it of some sort. I'm more of a Perl guy than Solaris, but depending on the shell you're using, you should be able to do something like:
TIME = 'date +%s' + 15
while TIME != `date +%s'
do whatever
And then just add a flag in the while loop, so that if it times out before completing, you can cite the timeout as reason for failure.
I suspect that the telnet has a timeout switch as well, but just off the top of my head, I think the above will work.
This uses telnet behind the scenes, and seems to work fine on mac/linux. It doesn't use netcat because of the differences between the versions on linux/mac, and this works with a default mac install.
Example:
$ is_port_open.sh 80 google.com
OPEN
$ is_port_open.sh 8080 google.com
CLOSED
is_port_open.sh
PORT=$1
HOST=$2
TIMEOUT_IN_SEC=${3:-1}
VALUE_IF_OPEN=${4:-"OPEN"}
VALUE_IF_CLOSED=${5:-"CLOSED"}
function eztern()
{
if [ "$1" == "$2" ]
then
echo $3
else
echo $4
fi
}
# cross platform timeout util to support mac mostly
# https://gist.github.com/jaytaylor/6527607
function eztimeout() { perl -e 'alarm shift; exec #ARGV' "$#"; }
function testPort()
{
OPTS=""
# find out if port is open using telnet
# by saving telnet output to temporary file
# and looking for "Escape character" response
# from telnet
FILENAME="/tmp/__port_check_$(uuidgen)"
RESULT=$(eztimeout $TIMEOUT_IN_SEC telnet $HOST $PORT &> $FILENAME; cat $FILENAME | tail -n1)
rm -f $FILENAME;
SUCCESS=$(eztern "$RESULT" "Escape character is '^]'." "$VALUE_IF_OPEN" "$VALUE_IF_CLOSED")
echo "$SUCCESS"
}
testPort
My machine does not support nc or /dev/tcp/$hostname/$port but timeout, so I came back to telnet as follows:
if echo "quit" | timeout 2 telnet $SERVER $PORT 2>&1 | grep -q 'Connected to'; then
echo "Connection to $SERVER on port $PORT succeeded"
exit 0
else
echo "Connection to $SERVER on port $PORT failed"
exit 1
fi
nmap-ncat to test for local port that is not already in use
availabletobindon() {
port="$1"
nc -w 2 -i 1 localhost "$port" 2>&1 | grep -v -q 'Idle timeout expired'
return "$?"
}
My connection is flaky, however I have a backup one. I made some bash script to check for connectivity and change connection if the present one is dead. Please help me improve them.
The scripts almost works, except for not waiting long enough to receive an IP (it cycles to next step in the until loop too quick). Here goes:
#!/bin/bash
# Invoke this script with paths to your connection specific scripts, for example
# ./gotnet.sh ./connection.sh ./connection2.sh
until [ -z "$1" ] # Try different connections until we are online...
do
if eval "ping -c 1 google.com"
then
echo "we are online!" && break
else
$1 # Runs (next) connection-script.
echo
fi
shift
done
echo # Extra line feed.
exit 0
And here is an example of the slave scripts:
#!/bin/bash
ifconfig wlan0 down
ifconfig wlan0 up
iwconfig wlan0 key 1234567890
iwconfig wlan0 essid example
sleep 1
dhclient -1 -nw wlan0
sleep 3
exit 0
Here's one way to do it:
#!/bin/bash
while true; do
if ! [ "`ping -c 1 google.com; echo $?`" ]; then #if ping exits nonzero...
./connection_script1.sh #run the first script
sleep 10 #give it a few seconds to complete
fi
if ! [ "`ping -c 1 google.com; echo $?`" ]; then #if ping *still* exits nonzero...
./connection_script2.sh #run the second script
sleep 10 #give it a few seconds to complete
fi
sleep 300 #check again in five minutes
done
Adjust the sleep times and ping count to your preference. This script never exits so you would most likely want to run it with the following command:
./connection_daemon.sh 2>&1 > /dev/null & disown
Have you tried omitting the -nw option from the dhclient command?
Also, remove the eval and quotes from your if they aren't necessary. Do it like this:
if ping -c 1 google.com > /dev/null 2>&1
Trying using ConnectTimeout ${timeout} somewhere.
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