How to ping in linux until host is known?

Question

How can I ping a certain address and when found, stop pinging.

I want to use it in a bash script, so when the host is starting up, the script keeps on pinging and from the moment the host is available, the script continues...

thanks! ;-)

Answer 1

Ping the target host once. Check if the ping succeeded (return value of ping is zero). If host is not alive, ping again.

The following code can be saved as a file and called with the hostname as argument, or stripped of the first and last line and used as function within an existing script (waitForHost hostname).

The code does not evaluate the cause for failure if the ping does not result in a response, thus looping forever if the host does not exist. My BSD manpage lists the meaning of each return value, while the linux one does not, so I guess this might not be portable, that's why I left it out.

#!/bin/bash

PING=`which ping`

function waitForHost
{
    if [ -n "$1" ]; 
    then
        waitForHost1 $1;
    else
        echo "waitForHost: Hostname argument expected"
    fi
}

function waitForHost1
{
    reachable=0;
    while [ $reachable -eq 0 ];
    do
    $PING -q -c 1 $1
    if [ "$?" -eq 0 ];
    then
        reachable=1
    fi
    done
    sleep 5
}
waitForHost $1

Answer 2

you can do a loop, send one ping and depending on the status break the loop, for example (bash):

while true; do ping -c1 www.google.com > /dev/null && break; done

putting this somewhere in your script will block, until www.google.com is pingable.

m

Answer 3

UNREACHEABLE=1;
while [ $UNREACHEABLE -ne "0" ]; 
   do ping -q -c 1 HOST &> /dev/null; UNREACHEABLE=$?; sleep 1;
done

You may remove sleep 1, it's only here to prevent any flooding problem in case where the host would be reacheable but ping would not exit with code 0.

Answer 4

A further simplification of Martynas' answer:

while ! ping -c1 www.google.com &>/dev/null; do :; done

note that ping itself (negated by !) is used as the loop test; as soon as it succeeds, the loop ends. The loop body is empty, with the null command ":" used to prevent a syntax error.

Answer 5

Please see good options at stackoverflow. Here is a sample in bash, you will have to loop over the following code until it returns a successfull ping result.

ping -c 1 -t 1 192.168.1.1;
if [ $? -eq 0 ]; then
    echo "192.168.1.1 is up";
else 
    echo "ip is down";
fi

Answer 6

any of the above loops can also be used with fping rather than ping which, IMO, is better suited for use in scripts than ping itself. see fping(8) for details.

while ! fping -q $HOSTNAMES ; do :; done

also useful for testing if machines are up before doing something on them. a simple example:

for h in HOST1 HOST2 HOST3 ; do
  if fping -q $h ; then
     echo -n "$h : "
     ssh $h "uname -a"
  fi
done