Tomcat java.net.BindException: Cannot assign requested address

I had a very strange error today when I tried to startup tomcat on some linux box that used to work. Since google was no help I figured I should document this somewhere.

Tomcat startup gave the notorious java.net.BindException: Cannot assign requested address. This usually means that another process is listening on the same port on this machine. I started with ps -ef grep java to make sure that no other tomcat process was running on the machine. Nothing.

I suspected that maybe some other web server was holding the port, but netstat -an showed that nothing binds this address. Moreover, telnet localhost 80 showed that no one is listening.

Looking at the server.xml I found out that the connector was binding to the hostname "demoserver" on port 80.

<Connector className="org.apache.coyote.tomcat4.CoyoteConnector"
address="demoserver" port="80" 
minProcessors="5" maxProcessors="75"
enableLookups="true" redirectPort="8443"
acceptCount="100" debug="0" connectionTimeout="20000"
useURIValidationHack="false" disableUploadTimeout="true" />

trying to ping demoserver gave me errors, but nslookup demoserver gave me the right ip address.

After a few minutes I noticed that some clown added demoserver to /etc/hosts with the wrong ip address. Fixing /etc/hosts to have the right ip address for demoserver made tomcat work smooth and nice.

mysqltop.sh

If you need to monitor mysql proccesslist, dump the following to a shell script and chmod 755. (ofcourse you will need to add passwords etc. if you have any;)

#!/bin/sh

watch 'mysql<<EOF
show processlist;
EOF
'

(Control+C will let you out)

Calcualting Average in UNIX Shell Script

I grabbed a piece of code to calculate an average for data in shell. It didn't work so I had to modify it. This is the result.

#!/bin/sh
n=0
sum=0
while read x
do
        sum=`echo $sum + $x | bc`
        if [ "$?" -eq "0" ]; then
                n=`expr $n + 1`
        fi
done
echo "scale=2;$sum/$n"| bc