Below is the easy way of installing drush in linux systems/servers.
#Add drush channel to pear list
pear channel-discover pear.drush.org
#Check whether is it added or not
pear remote-list -c drush
#Then run install command as below
pear install drush/drush
pear install drush/package_name (or version_name)
Now enjoy running Drush commands straight away without any further configuration :)