Linux ifconfig can add ip address real time, but system reboot, the IP Adddress will be gone. If need permanently set in system, need to edit the config file at
[Redhat or CentOS] /etc/sysconfig/network-scripts/ifcfg-eth0
[Ubuntu or Debian] /etc/network/interfaces
ifconfig eth0 192.168.1.x netmask 255.255.25.0
