10 basic examples of linux netstat command

Netstat

Netstat is a command line utility that can be used to list out all the network (socket) connections on a system. It lists out all the tcp, udp socket connections and the unix socket connections.
 
Apart from connected sockets it can also list listening sockets that are waiting for incoming connections. So by verifying an open port 80 you can confirm if a web server is running on the system or not. This makes it a very useful tool for network and system administrators.

In this tutorial we shall be checking out few examples of how to use netstat to find information about network connections and open ports on a system.

Here is a quick intro to netstat from the man pages

netstat - Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships

رکورد RP در DNS چیست؟

Error: Postfix - do not list domain example.com in BOTH mydestination and virtual_mailbox_domains

In my case, at least, removing mydomain.com from mydestination cleared things up. On my server, mydestination is just localhost, localhost.localdomain

GREAT SOLUTION, works for me.

Inspecting Postfix’s email queue.

1-  Display a list of queued mail

mailq

or

postqueue -p

To save the output to a text file you can run

mailq > myfile.txt

or

postqueue -p > myfile.txt

How to clean log file?

> logfile

or

cat /dev/null > logfile

دستورات کاربردی لینوکس

wc	wc, or "word count," prints a count of newlines, words, and bytes for each input file.

Change The Color of My Shell Prompt Under Linux or UNIX Permanently

$ cd
$ vi .bash_profile

OR
$ vi $HOME/.bashrc
Append the following line:
export PS1="\e[0;31m[\u@\h \W]\$ \e[m"
Save and close the file.

To do this changing you must logout an login again.

A list of color codes

Color	Code
Black	0;30
Blue	0;34
Green	0;32
Cyan	0;36
Red	0;31
Purple	0;35
Brown	0;33
Blue	0;34
Green	0;32
Cyan	0;36
Red	0;31
Purple	0;35
Brown	0;33

Note: You need to replace digit 0 with 1 to get light color version.

----------------------------- In Ubuntu 14.4 --------------------------

Run the following command in a terminal:

gedit ~/.bashrc

When .bashrc opens, locate and uncomment force_color_prompt=yes (that is, remove the hash, so it no longer looks like: #force_color_prompt=yes).

Save the file, and open a new terminal window, and you should already see a change (the prompt should be Light Green, which is defined by 1;32). You can then change any colour value you like; eg: 0;35 = Purple.

To edit the colour values, locate the following section, and change the default values with some of the examples listed further down:

if [ "$color_prompt" = yes ]; then
    PS1=’${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;31m\]\w\[\033[00m\]\$ ‘
else
    PS1=’${debian_chroot:+($debian_chroot)}\u@\h:\w\$ ‘
fi

You can check out this Bash colour chart for a full range of colour values, but here are a few basic ones you can play around with (note that “Light” isn’t what you might think – it actually means “bold”): Black 0;30 – Dark Gray 1;30 – Blue 0;34 – Light Blue 1;34 – Green 0;32 – Light Green 1;32 – Cyan 0;36 – Light Cyan 1;36 – Red 0;31 – Light Red 1;31 – Purple 0;35 – Light Purple 1;35 – Brown 0;33 – Yellow 1;33 – Light Gray 0;37 – White 1;37

For example, here is the line that I use it:

PS1='${debian_chroot:+($debian_chroot)}\[\033[01;35m\]\u@\h\[\033[00m\]:\[\033[01;34m\] \w\[\033[01;37m\] > '

ایجاد Virtual Hosting در آپاچی

root@www:~# vi /etc/apache2/sites-available/virtual.host

# create a file for virtual.host

 <VirtualHost *:80>

    ServerName www.virtual.host

    ServerAdmin [e-mail]

    DocumentRoot /home/wheezy/public_html

    ErrorLog /var/log/apache2/virtual.host.error.log

    CustomLog /var/log/apache2/virtual.host.access.log combined

    LogLevel warn

</VirtualHost>

root@www:~# a2ensite virtual.host 

Enabling site virtual.host.

To activate the new configuration, you need to run:

  service apache2 reload

root@www:~# service apache2 reload

خطا در Apache Virtual Hosting

در زمان اضافه کردن یک virtual host در آپاچی ممکن است این خطا مشاهده شود.

خطای داده شده :

root@tsrv:~# a2ensite vh.postfixhelp.html

ERROR: Site vh.postfixhelp.html does not exist!

راه حل:

a2ensite is simply a perl script that only works with filenames ending .conf

Therefore, I have to rename my setting file for mysite.com to mysite.com.conf as might be achieved as follows:

mv /etc/apache2/sites-available/mysite.com /etc/apache2/sites-available/mysite.com.conf

Success

Testing SMTP, POP3 and IMAP protocol access for Postfix Mail Service

SMTP

telnet: > telnet mx1.example.com smtp
telnet: Trying 192.0.2.2...
telnet: Connected to mx1.example.com.
telnet: Escape character is '^]'.
server: 220 mx1.example.com ESMTP server ready Tue, 20 Jan 2004 22:33:36 +0200
client: HELO client.example.com
server: 250 mx1.example.com
client: MAIL from: <[e-mail]>
server: 250 Sender <[e-mail]> Ok
client: RCPT to: <[e-mail]>
server: 250 Recipient <[e-mail]> Ok
client: DATA
server: 354 Ok Send data ending with <CRLF>.<CRLF>
client: From: [e-mail]
client: To: [e-mail]
client: Subject: Test message
client: 
client: This is a test message.
client: .
server: 250 Message received: [e-mail]
client: QUIT
server: 221 mx1.example.com ESMTP server closing connection