Linux

Linux basic commands

Before are some basic linux commands to keep you going.

ifconfig Commands: This is needed to Configure Network Interface in Linux. ifconfig in simply means interface configuration.utility for system/network administration in Unix/Linux operating systems to configure, manage and query network interface parameters via command line interface or in a system configuration scripts.

The “ifconfig” command is used for displaying current network configuration information, setting up an IP address, netmask or broadcast address to a network interface, creating an alias for the network interface, setting up hardware address and enable or disable network interfaces.

1. ifconfig
The “ifconfig” command with no arguments will display all the active interface details. The ifconfig command also used to check the assigned IP address of a server.

root@pve:~# ifconfig
eth0 Link encap:Ethernet HWaddr 08:00:xx:69:73:bd

2. Display Information of All Network Interfaces
ifconfig command with -a argument displays information of all active or inactive network interfaces on the server.

root@pve:~# ifconfig -a

3.View Network Settings of Specific Interface
Using the interface name (eth0) as an argument with the “ifconfig” command will display details of specific network interface.
root@pve:~# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 08:00:xx:69:73:xx
inet6 addr: fe80::a00:xxxx:fe69:73bd/64 Scope:Link

4.Enabling an Network Interface
The “up” or “ifup” flag with interface name (eth0) activates a network interface, if it is not in active state and allowing to send and receive information. For example, “ifconfig eth0 up” or “ifup eth0” will activate the eth0 interface.

root@pve:~# ifconfig eth0 up
root@pve:~#
root@pve:~# !both commands can be used to achieve the same result.
root@pve:~#
root@pve:~# ifup eth0

5.Disabling an Network Interface
root@pve:~# ifconfig eth0 down.
The semaphore timeout period has expired.
root@pve:~# !both commands can be used to achieve the same result to shutdown as well.
root@pve:~#
root@pve:~#ifdown eth0

6. Assigning an IP Address to a Network Interface
To assign an IP address to a specific interface, use the following command with an interface name (eth0) and ip address that you want to set.
root@pve:~# ifconfig eth0 172.xx.25.1xx
This will set the IP address to interface eth0

7. Assigning an IP Address to a Netmask to Network Interface
Using the “ifconfig” command with “netmask” argument and interface name as (eth0) allows you to define a netmask to a given interface.
For example, “ifconfig eth0 netmask 255.255.xxx.22x” will set the network mask to a given interface eth0.

root@pve:~# ifconfig eth0 netmask 255.255.xxx.22x

8. How to Assign a Broadcast to Network Interface
Using the “broadcast” argument with an interface name will set the broadcast address for the given interface.
For example, “ifconfig eth0 broadcast 172.xx.25.xx” command sets the broadcast address to an interface eth0.
root@pve:~# ifconfig eth0 broadcast 172.xx.25.xxx

9. How to Assign a IP, Netmask and Broadcast to Network Interface
To assign an IP address, Netmask address and Broadcast address all at once using “ifconfig” command with all arguments as given below.

root@pve:~# ifconfig eth0 172.xx.25.xx netmask 255.255.xxx.xx broadcast 172.xx.25.xx

10. How to Change MTU for a Network Interface
The “mtu” argument sets the maximum transmission unit to an interface.
The MTU allows you to set the limit size of packets that are transmitted on an interface. The MTU able to handle a maximum number of octets to an interface in one single transaction. For example, “ifconfig eth0 MTU 1000” will set the maximum transmission unit to a given set (i.e. 1000). Not all network interfaces support MTU settings.

root@pve:~#ifconfig eth0 mtu 1000

11. How to Enable Promiscuous Mode
What happens in normal mode, when a packet received by a network card,
it verifies that the packet belongs to itself. If not, it drops the packet normally, but in the promiscuous mode is used to accept all the packets that flows through the network card.

Most of the today’s network tools uses the promiscuous mode to capture and analyze the packets that flows through the network interface.
To set the promiscuous mode, use the following command.

root@pve:~#ifconfig eth0 promisc


12. How to Disable Promiscuous Mode
To disable promiscuous mode, use the “-promisc” switch that drops back the network interface in normal mode.
root@pve:~#ifconfig eth0 -promisc

13. How to Change the MAC address of Network Interface
To change the MAC (Media Access Control) address of an eth0 network interface, use the following command with the argument “hw ether“.

root@pve:~#ifconfig eth0 hw ether AA:BB:CC:DD:EE:FF

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