How to import the public.gpg.key for yum
[root@midhun~]# yum update sendmail
Repository base already added, not adding again You have enabled checking of packages via GPG keys. This is a good thing.However, you do not have any GPG public keys installed. You need to download the keys for packages you wish to install and install them.You can do that by running the command:
rpm --import public.gpg.key
Alternatively you can specify the url to the key you would like to usefor a repository in the 'gpgkey' option in a repository section and yum will install it for you. For more information contact your distribution or package provider.

When you get the above message, just import it from web (Here I am using CentOS) as shown below

[root@midhun ~]# rpm --import http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-4

MySQL Replication
1. Settings to be done in Master DB server:

Edit my.cnf file (/etc/my.cnf) and enter the following:
server-id = 1
log-bin

2. Login to mysql DB in master server and run the following command:
mysql> show master status;
Note down the following values: MASTER_LOG_FILE & MASTER_LOG_POS
Then give permission for the slave server
mysql>GRANT REPLICATION SLAVE ON *.* TO user@slave_IP IDENTIFIED BY 'password';
mysql>GRANT FILE ON *.* to user@ slave__IP identified by 'password';
3. Take the DB dump in master server and restore it in slave server.
4. Edit my.cnf file in slave server (/etc/my.cnf) and enter the following:
server-id = 2
master-host = Master_Server_IP
master-user = user
master-password = password
log-warnings
5. Login to mysql DB in slave server and run the following command:
mysql>CHANGE MASTER TO MASTER_HOST='Master_Server_IP', MASTER_USER='user',
MASTER_PASSWORD='password',
MASTER_LOG_FILE='Log filename',
MASTER_LOG_POS= number;
mysql>start slave;
6. Restart mysql service in both the servers.