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(Linux Command Line) Part 4 - Commands Line for Network Configurationin Linux (CentOS, Ubuntu)

Linux is an open source Operating System, mainly used on servers and mainframes due to its high stability, secured and free. This is part 4 of the serial Linux Command Line - Commands Line for Network Configuration in Linux (CentOS, Ubuntu)

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Commands Line for Network Configurationin Linux (CentOS, Ubuntu)

1) Commands Line for Network Configuration in Linux (CentOS, Ubuntu)

Ubuntu, CentOS, and other Linux operating systems consider a network card as a device. They save the configuration in the text file, then load it every time the system boots up. Each computer needs a wired or wireless Ethernet card, listed in the /dev directory with a name beginning with three letters Eth, for example, eth0 for the first network card, eth1 for the second network card...
The Network configuration files of CentOS and Ubuntu are usually different. For example, in Ubuntu, the network configuration file is stored in /etc/network/interface/ while in CentOS, it is stored in /etc/sysconfig/network- Scripts/

1.1. Commands for Checking network information in CentOS and Ubuntu

COMMANDPURPOSE / DESCRIPTION
  ifconfig -a | grep ethCheck the total number of network cards in the system
  ifconfigCheck the configuration (MAC, IP address, gateway ..) of all the network card in the machine
(similar to the IPCONFIG command in Windows)
  ifconfig card-nameCheck the configuration of the network card named card-name (eg: ifconfΓ¬g eth0)
  route -nCheck the route of packets (similar to the ROUTE command in Windows)

1.2. Commands for Network Configuration in CentOS and Ubuntu

COMMANDPURPOSE / DESCRIPTION
  sudo ifconfig eth0 upEnable the network card eth0 in Ubuntu
  sudo ifconfig eth0 downDisable the network card eth0 in Ubuntu
 ifconfig card IP1 netmask IP2Set the network configuration for a network card. For example, to set the IP for eth0 to 192.168.1.100, netmask= 255.255.255.0 with this command: ifconfig eth0 192.168.1.2 netmask 255.255.255.0
Warning: This configuration will be reset/ deleted after the system re-start
 vi /etc/network/interfacesSet up the network configuration file in Ubuntu with VI Text Editor
 vi  /etc/sysconfig/network-scripts/ifcfg-eth0Set up the configuration for network card Eth0 in CentOS with VI Text Editor
 /etc/init.d/networking restartRestart the network card in Ubuntu (to apply changes)
 service network restartRestart the network card in CentOS (to apply changes)
  vi /etc/resolvSet name servers for CentOS and Ubuntu. For example:
nameserver 8.8.8.8
nameserver 8.8.4.4
 route add default gw 192.168.1.1Set 192.168.1.1 as the default gateway in Ubuntu. In contrast to the command Add, we use the command Delete (for example: route delete default gw 192.168.1.1)
  route add -net 192.168.5.0 mask 255.255.255.0 dev eth0Add a static routing to the network (for the network card Eth0). In contrast to the command Add, we use the command Delete

1.3. Other Command Line for Networking in CentOS and Ubuntu

COMMANDPURPOSE / DESCRIPTION
 netstatDisplay network connections (same in Windows)
 traceroute serverATrace packet routing to serverA
 nslookupQuery the domain server (name server)
 rlogin serverAConnect to a remote system
  telnet serverAConnect to a remote system (better interacting than rlogin)
 rcp fileX serverACopy a file (fileX) from the remote server (serverA)
 ftp
Transfer files between systems on a network
 rsh commandA
Run a command on a remote system without logging in
 ping serverA
Check connection to a remote system (same in Windows)
 lcd path
Change local folder when logged in on remote machine
 mesg y/n
Set options for other users to write messages for you
 write user
Send a message to another user
 talk userAllow 2 people to chat with each other

Now I will guide in detail how to use the above commands to configure the network for CentOS and Ubuntu

2) Guide how to Configure the network in CentOS and Ubuntu

Guide how to setup the network configuration in CentOS and Ubuntu

2.1. Configure network in Ubuntu

Step 1: Open the configuration file with VI text editor
sudo vi /etc/network/interfaces
Your screen will display the network configuration like this:
auto lo
iface lo inet loopback
auto eth0
iface eth0 inet static
address 192.168.1.2
netmask 255.255.255.1.0
gateway 192.168.1.1
=> You can replace the "red text" above with your IP

If you want to use a dynamic IP from the DHCP server, we declare the following commands in the file /etc/network/interfaces:
auto lo
iface lo inet loopback
auto eth0
iface eth0 inet dhcp
Step 2: Reboot or Restart the Networking service by using the following command:
/etc/init.d/networking restart
Step 3: In most cases, your network device will work well after step 2. But in some case, you have to config the Nameserver. Here's how:
sudo vi /etc/resolv.conf
Enter the contents of the file as below then Save it
nameserver 8.8.8.8
nameserver 8.8.8.4
Done !!

2.2. Configure network in CentOS

Step 1: Use the command ifconfig to check your network cards

Step 2: Specify which network card to config (for example: Eth0), then open the configuration file with VI text editor
vi  /etc/sysconfig/network-scripts/ifcfg-eth0
Your screen will display the network configuration like this:
DEVICE=eth0
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=none
BROADCAST=192.168.1.255
HWADDR=00:25:90:C3:65:BC
IPADDR=192.168.1.100
NETMASK=255.255.255.0
GATEWAY=192.168.1.1
DNS1=8.8.8.8
=> You can replace the "red text" above with your IP
If you want to use a dynamic IP from the DHCP server, we need to change the file contents to:
DEVICE=eth0
TYPE=Ethernet
ONBOOT=yes
NM_CONTROLLED=yes
BOOTPROTO=DHCP
DNS1=8.8.8.8
Step 2: Reboot or Restart the Networking service by using the following command:
/etc/init.d/networking restart
All done !!
Feel free to leave a comment if you need any help.

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