Linux administration activities are similar to any Unix system.
The important components are hardware device administration, files system, users administration, programs packs administration, services administration, system security ensuring and automation tasks.

Most of system administrator interactions with Linux operating system will be done through the command line interface (shell) and text configuration files.

The components of a GNU / Linux / Distributions

An GNU/Linux operating system consists of core (kernel), Linux and applications running over it.
One of the most significant application is the command interpreter (the shell). On most of Linux distributions the shell is Bash.
The shell acts as an intermediary between user and core. The shell transforms users command in to process which is using the core to complete a task.

Other basic applications are the editor(vim, emacs), compilers, libraries. Generally graphic applications are missing from a server system realizing interaction almost exclusively via command line.

Unlike other operating systems kernel and application development is performed differently.
The aggregation of these components is made by a GNU/Linux distribution. There are hundreds of Linux distributions, among the most popular we mention Ubuntu Fedora/RedHat, SuSE, Debian, Gento, Slackware etc.

Some of the distributions are similar such as Debian-based :
Debian, Ubuntu, MEPIS, Damn Small Linux, Xandros, Linspire. These distributions use software packages provided by Debian and APT system.

Temporary  Network configuration

Linux provides two utilities to configure network interfaces. This configuration is lost after reboot.

The first of these is called ifconfig. Present on all Unix platforms, this tool enables the IP address, a network mask and broadcast address.
The ifconfig command can be used both to inspect the current network configuration, the operating parameters: MTU, number of packs sent, number of packs received.

For each physical network interface can be defined more logical interfaces known as subinterface.
Logically, each subinterface of a router is a distinct interface. For this reason, two subinterfaces can not have the same IP subnetwork.

All network parameters restarts when the interface stops, interface that can be made for a specific interface or network service restart. This results leads to resetting all network interfaces.
Temporary network configurations will be lost if the interface deactivated. In a subinterface case, deactivation is equivalent to removing.Starting from kernel version 2.2, came a package of utilities for handling network configuration known as iproute.


# ifconfig eth0

eth0 Link encap:Ethernet HWaddr 00:2D:32:5E:3B:3C
inet addr: Bcast: Mask:
RX packets:977839669 errors:0 dropped:1990 overruns:0 frame:0
TX packets:1116825094 errors:8 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1594112309 (1.5 GiB) TX bytes:1535889321 (1.8 GiB)
Interrupt:185 Base address:0xdc00


Display Details of All interfaces Including Disabled Interfaces

# ifconfig -a

Shutdown an Interface

# ifconfig eth0 down

Enable an Interface

# ifconfig eth0 up

Assign as the IP address for the interface eth0.

# ifconfig eth0

Change Subnet mask of the interface eth0.

# ifconfig eth0 netmask

Change Broadcast address of the interface eth0.

# ifconfig eth0 broadcast

Assign ip-address, netmask and broadcast at the same time to interface eht0.

# ifconfig eth0 netmask broadcast

Now the second version (iproute2) is a strong alternative allowing very sophisticated settings. To configure the network parameters is used ip addr utility which is part of the package iproute .

To configure an interface is necessary to specify the IP address, the network area code and the broadcast address.

To define configurations for subinterfaces label option is used. For compatibility reasons, it is recommended that names to start with the interface name labels. So, for eth0 label shall be valid: eth00, eth0.0, eth 0: 0, eth 0.

Since ifconfig sees the labels as a virtual interface, it can run only with the interface: number type. To enable or disable an interface or deleting logical configurations associated with a subinterface is used other utility of the iproute2 : ip link package .

Ip link tool can be useful to change the data link level parameters (MAC, MTU, etc) and to display these parameters.
Besides handling functions defining routing table and tunnels, iproute2 provides support for traffic policy.

Permanent configuration

To set up a permanent network parameters is used /etc/ network/interfaces
This file is specific to Debian (its location in other distributions may be different) and contains information necessary to configure network interfaces.

Programs using this file shall be ifup and ifdown and shall be run from /etc/init.d/networking, script responsible for the network configuration in the boot of the operating system. To define static parameters of network administrator can specify IP address, subnet mask, default gateway address, name server addresses, or some of these parameters. Can also be specified other actions to be performed when the interface is started, that stopped.