I am a new Ubuntu Linux laptop user. I setup my computer name to ‘tom’ during installation but now I would like to change the computer name to ‘jerry’. Can you tell me how do I I remove tom and set it to jerry on Ubuntu Linux? How do I change the Ubuntu computer name from ‘ubuntu’ to ‘AvlinStar’? Can you tell me more about Ubuntu Linux change hostname command?

You can use the hostname command to see or set the system’s host name. The host name or computer name is usually at system startup in /etc/hostname file. Open the terminal application and type the following commands to set or change hostname or computer name on Ubuntu.

Display the current Ubuntu hostname

Simply type the following command:
$ hostname
Sample outputs:

Ubuntu change hostname command

The procedure to change the computer name on Ubuntu Linux:

1. Type the following command to edit /etc/hostname using nano or vi text editor:
   sudo nano /etc/hostname
   Delete the old name and setup new name.
2. Next Edit the /etc/hosts file:
   sudo nano /etc/hosts
   Replace any occurrence of the existing computer name with your new one.
3. Reboot the system to changes take effect:
   sudo reboot

Sample outputs:

How to change the Ubuntu server hostname without a system restart?

Type the following commands:
$ sudo hostname new-server-name-here
Next edit the /etc/hostname file and update hostname:
$ sudo nano /etc/hostname
Finally, edit the /etc/hosts file and update the lines that reads your old-host-name:
$ sudo nano /etc/hosts
From:
127.0.1.1 old-host-name
To:
127.0.1.1 new-server-name-here
Save and close the file.

Ubuntu Linux Change Hostname Using hostnamectl

Systemd based Linux distro such as Ubuntu Linux 16.04 LTS and above can simply use the hostnamectl command to change hostname. To see current setting just type the following command:
$ hostnamectl
Sample outputs:

   Static hostname: nixcraft
         Icon name: computer-laptop
           Chassis: laptop
        Machine ID: 291893e6499e4d99891c3cf4b70a138b
           Boot ID: 9fda2365b77841649e40a141fde46537
  Operating System: Ubuntu 17.10
            Kernel: Linux 4.13.0-21-generic
      Architecture: x86-64

To change hostname from nixcraft to viveks-laptop, enter:
$ hostnamectl set-hostname viveks-laptop
$ hostnamectl

Le logiciel pure-ftpd est l’un des serveurs FTP les plus simple à installer et configurer c’est pourquoi si vous cherchez à installer un serveur FTP rapidement sur votre serveur Linux, je ne peux que vous le recommander.
Aujourd’hui, nous allons voir comment utiliser pure-ftpd et MySQL simultanément pour permettre la séparation des tâches avec l’enregistrement des comptes utilisateurs dans la base de données et le reste du fonctionnement gérer par pure-ftpd. Le but du tutoriel n’étant pas de vous apprendre à installer et manipuler MySQL, je pars du principe que ce dernier est installé sur la même machine (ou une machine distante) que votre serveur FTP et que vous avez soit MySQL Workbench sous la main ou le client MySQL en ligne de commande pour la partie traitant des manipulations sur la base de donnée.

Installation du serveur Pure-FTPd-mysql

Pour utiliser MySQL avec votre serveur de FTP, il faut que ce dernier ai été compilé avec la commande “–with-mysql“. Heureusement pour nous, plutôt que de ce compliquer la vie à compiler les sources du serveur, nous allons directement installer le paquet tout prêt à l’usage nommé : pure-ftpd-mysql.
Même si on vous conseil d’installer “pure-ftpd” ou même qu’on vous demande de le désinstaller si vous l’avez déjà installé, dite oui pour continuer l’installation.

sudo apt install pure-ftpd-mysql

Note : Si vous avez votre serveur FTP déjà en cours de production, l’installation de cette version ne perturbera en rien vos utilisateurs et vous pouvez continuer la suite de ce tutoriel puisque le redémarrage ne sera nécessaire qu’à la fin.

Création de la Base de données

A partir de votre interface PHPMyAdmin ou du client MySQL, vous allez créer un utilisateur ainsi qu’une base de données associés à ce compte.

Création d’un compte utilisateur en requête SQL.

CREATE USER 'pureftpd' identified by 'pwdftp';

Création de la base de donnée et une table qui servira à contenir les comptes utilisateurs.

CREATE DATABASE pureftpd;

Association du compte utilisateur “pureftpd” avec la table “users” en lui attribuant les droits de lecture, écriture, mise à jour et suppression.

GRANT SELECT, INSERT, UPDATE, DELETE ON '*.pureftpd' TO 'pureftpd';

Création de la table où les utilisateurs seront enregistrés.

CREATE TABLE users (
Id int(11) NOT NULL auto_increment PRIMARY KEY,
User varchar(32) NOT NULL default '' UNIQUE KEY,
Password varchar(64) NOT NULL default '',
Uid int(3) NOT NULL default 33,
Gid int(3) NOT NULL default 33,
Dir varchar(255) NOT NULL default '',
QuotaSize int(4) NOT NULL default 250,
ULBandwidth int(2) NOT NULL default 10,
DLBandwidth int(2) NOT NULL default 10
);

Packet Analyzer: efficient network traffic analysis

tcpdump command is also called as packet analyzer.

tcpdump command will work on most flavors of unix operating system. tcpdump allows us to save the packets that are captured, so that we can use it for future analysis. The saved file can be viewed by the same tcpdump command. We can also use open source software like wireshark to read the tcpdump pcap files.

In this tcpdump tutorial, let us discuss some practical examples on how to use the tcpdump command.

1. Capture packets from a particular ethernet interface using tcpdump -i

When you execute tcpdump command without any option, it will capture all the packets flowing through all the interfaces. -i option with tcpdump command, allows you to filter on a particular ethernet interface.

$ tcpdump -i eth1
14:59:26.608728 IP xx.domain.netbcp.net.52497 > valh4.lell.net.ssh: . ack 540 win 16554
14:59:26.610602 IP resolver.lell.net.domain > valh4.lell.net.24151:  4278 1/0/0 (73)
14:59:26.611262 IP valh4.lell.net.38527 > resolver.lell.net.domain:  26364  PTR? 244.207.104.10.in-addr.arpa. (45)

In this example, tcpdump captured all the packets flows in the interface eth1 and displays in the standard output.

Note: Editcap utility is used to select or remove specific packets from dump file and translate them into a given format.

2. Capture only N number of packets using tcpdump -c

When you execute tcpdump command it gives packets until you cancel the tcpdump command. Using -c option you can specify the number of packets to capture.

$ tcpdump -c 2 -i eth0
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
14:38:38.184913 IP valh4.lell.net.ssh > yy.domain.innetbcp.net.11006: P 1457255642:1457255758(116) ack 1561463966 win 63652
14:38:38.690919 IP valh4.lell.net.ssh > yy.domain.innetbcp.net.11006: P 116:232(116) ack 1 win 63652
2 packets captured
13 packets received by filter
0 packets dropped by kernel

The above tcpdump command captured only 2 packets from interface eth0.

Note: Mergecap and TShark: Mergecap is a packet dump combining tool, which will combine multiple dumps into a single dump file. Tshark is a powerful tool to capture network packets, which can be used to analyze the network traffic. It comes with wireshark network analyzer distribution.

3. Display Captured Packets in ASCII using tcpdump -A

The following tcpdump syntax prints the packet in ASCII.

$ tcpdump -A -i eth0
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
14:34:50.913995 IP valh4.lell.net.ssh > yy.domain.innetbcp.net.11006: P 1457239478:1457239594(116) ack 1561461262 win 63652
E.....@.@..]..i...9...*.V...]...P....h....E...>{..U=...g.
......G..7 KA....A...L.
14:34:51.423640 IP valh4.lell.net.ssh > yy.domain.innetbcp.net.11006: P 116:232(116) ack 1 win 63652
E.....@[email protected]...*.V..*]...P....h....7......X..!....Im.S.g.u:*..O&....^#Ba...
E..(R.@.|.....9...i.*...]...V..*P..OWp........

Note: Ifconfig command is used to configure network interfaces

Lire la suite…

rsync stands for remote sync.

rsync is used to perform the backup operation in UNIX / Linux.

rsync utility is used to synchronize the files and directories from one location to another in an effective way. Backup location could be on local server or on remote server.

Important features of rsync

• Speed: First time, rsync replicates the whole content between the source and destination directories. Next time, rsync transfers only the changed blocks or bytes to the destination location, which makes the transfer really fast.
• Security: rsync allows encryption of data using ssh protocol during transfer.
• Less Bandwidth: rsync uses compression and decompression of data block by block at the sending and receiving end respectively. So the bandwidth used by rsync will be always less compared to other file transfer protocols.
• Privileges: No special privileges are required to install and execute rsync

Syntax

$ rsync options source destination

Source and destination could be either local or remote. In case of remote, specify the login name, remote server name and location.

Example 1. Synchronize Two Directories in a Local Server

To sync two directories in a local computer, use the following rsync -zvr command.

$ rsync -zvr /var/opt/installation/inventory/ /root/temp
building file list ... done
sva.xml
svB.xml
.
sent 26385 bytes  received 1098 bytes  54966.00 bytes/sec
total size is 44867  speedup is 1.63
$

In the above rsync example:

• -z is to enable compression
• -v verbose
• -r indicates recursive

Now let us see the timestamp on one of the files that was copied from source to destination. As you see below, rsync didn’t preserve timestamps during sync.

$ ls -l /var/opt/installation/inventory/sva.xml /root/temp/sva.xml
-r--r--r-- 1 bin  bin  949 Jun 18  2009 /var/opt/installation/inventory/sva.xml
-r--r--r-- 1 root bin  949 Sep  2  2009 /root/temp/sva.xml

Example 2. Preserve timestamps during Sync using rsync -a

rsync option -a indicates archive mode. -a option does the following,

• Recursive mode
• Preserves symbolic links
• Preserves permissions
• Preserves timestamp
• Preserves owner and group

Now, executing the same command provided in example 1 (But with the rsync option -a) as shown below:

$ rsync -azv /var/opt/installation/inventory/ /root/temp/
building file list ... done
./
sva.xml
svB.xml
.
sent 26499 bytes  received 1104 bytes  55206.00 bytes/sec
total size is 44867  speedup is 1.63
$

As you see below, rsync preserved timestamps during sync.

$ ls -l /var/opt/installation/inventory/sva.xml /root/temp/sva.xml
-r--r--r-- 1 root  bin  949 Jun 18  2009 /var/opt/installation/inventory/sva.xml
-r--r--r-- 1 root  bin  949 Jun 18  2009 /root/temp/sva.xml

Lire la suite…

Source: Akamai

iptables is an application that allows users to configure specific rules that will be enforced by the kernel’s netfilter framework. It acts as a packet filter and firewall that examines and directs traffic based on port, protocol and other criteria. This guide will focus on the configuration and application of iptables rulesets and will provide examples of ways they are commonly used.

By default, the iptables tool is included with your Linode-supplied distribution. In order to use iptables, you will need root (sudo) privileges.

Use Linux iptables to Manage IPv4 Traffic

The iptables Command

Many options can be used with the iptables command. As stated above, iptables sets the rules that control network traffic. You can define different tables to handle these rules through chains, lists of rules that match a subset of packets. The table contains a variety of built-in chains, but you can add your own.

Basic iptables Parameters and Syntax

Before we begin creating rules, let’s review the syntax of an iptables rule.

For example, the following command adds a rule to the beginning of the chain that will drop all packets from the address 198.51.100.0:

iptables -I INPUT -s 198.51.100.0 -j DROP

The sample command above:

1. Calls the iptables program
2. Uses the -I option for insertion. Using a rule with the insertion option will add it to the beginning of a chain and will be applied first. To indicate a specific placement in the chain, you may also use a number with the -I option.
3. The -s parameter, along with the IP address (198.51.100.0), indicates the source.
4. Finally, the -j parameter stands for jump. It specifies the target of the rule and what action will be performed if the packet is a match.

Lire la suite…