Beginner Linux HowTo’s | LinuxDynasty

Using netstat to find active network connections

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May 242008

To list all open network ports on your machine, run netstat -lnptu. Here is a breakdown of the parameters:

l – List all listening ports
n – Display the numeric IP addresses (i.e., don’t do reverse DNS lookups)
p – List the process name that is attached to that port
t – List all TCP connections
u – List all UDP connections

In this example, there are a number of open ports. For example, you can see:

print server (lpd on port 515)
rsync server (rsyncd on port 873)
database server (mysqld on localhost port 3306)
web server (httpd on port 80)
dns server (named on port 53)
openssh (sshd on port 22)
syslog (syslog-ng on port 514)
snmp (snmpd on port 161)
dhcp server (dhcpd on port 67)
tftp server (in.tftpd on port 69)
time server (ntpd on port 123)
several services related to importing an NFS filesystem

You can also change the "l" to an "a" to list both listening and active ports.

You can also use netstat to show the current routing table by running netstat -rn:

HowTo use “wget” to check that a website is up

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May 242008

Here’s a very cool command that will let you know that a website is up and tell you the throughput. Being a network guy I always wondered how those Linux geeks, uh I meant guys and gals could spit that information out so quickly when we’d be on the phone troubleshooting.

Well the secret is out my Networking buddies. And that secret is "wget". Now I can kick that information out in split seconds too! Check this out.

[root@mylinuxbox ~]# wget www.yahoo.com
–22:50:27– http://www.yahoo.com/
Resolving www.yahoo.com… 69.147.76.15
Connecting to www.yahoo.com|69.147.76.15|:80… connected.
HTTP request sent, awaiting response… 200 OK
Length: 9562 (9.3K) [text/html]
Saving to: `index.html.3′

100%[=======================================>] 9,562 –.-K/s in 0.03s

22:50:27 (352 KB/s) – `index.html.3′ saved [9562/9562]

Now is that cool or what? And you better not call me a geek.

Synergy How To

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Feb 102008

You really got to love synergy, since it is the only App I know of that can share a mouse and keyboard across multiple boxes/Operating systems

FYI, this tutorial assumes that you know basic linux/windows and how to download the software/install

- You need at minimum 2 section statements, one for the screens section and the other for the links section
- In the screens section you will put the hostname of the boxes that will be involved in synergy.(if you do not have the hostname in DNS, then input the hostname in (/etc/hosts for linux and C:WINDOWSsystem32driversetchost in windows)
- Now that you have the hostnames in now it is time to configure the links section. In this section all you have to do is put in the hostnames of the box and what direction to the next box they are in… example.. chewy is left of chewbaca and chewbaca is right of chewy.
- Create this file if it does not exist..
  /etc/synergy.conf
```
section: screens
  chewy:
  chewbaca:

end

section: links
  
  chewy:
    left = chewbaca

  chewbaca:
    right = chewy

end
  
```
- Now, I personally boot into multiuser mode, so I will describe the steps associated with that. 1st edit your $HOME/.xinitrc.. Mine looks like this
```
exec gnome-session &
synergyc -f chewy
  
```
- Now you can substitute gnome-session with startkde or what ever window manager you prefer.
- The line "synergyc -f chewy", this is where the connection to the box that is in charge of the mouse and keyboard.
- Now you can run startx and it will try to connect to the synergy server in charge of the mouse and keyboard. Now we are off to the windows section.
- Run synergy, click the "Share this computer and mouse(server) button
- Click configure, then add the screens to there appropriate positions like you did in linux.
- now after you applied the settings click on start of the main synergy window
Example… WINDOWS STYLE

How to setup serial console on linux

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Feb 102008

This tutorial is for those Admins who need to setup serial console on there LINUX servers

Section-1

- First step is to make sure you have a serial port.
- Second step is to make sure you have a console cable. You can do this by running this..
```
linuxdynasty.org]# dmesg |grep ttyS0
ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
  
```

hardware

Add this co:2345:respawn:/sbin/agetty ttyS0 9600 vt100-nav to /etc/inittab
using your favorite editor. (mine is vi

) This is how mine looks like..

# Run gettys in standard runlevels
co:2345:respawn:/sbin/agetty ttyS0 57600 vt100-nav
1:2345:respawn:/sbin/mingetty tty1
2:2345:respawn:/sbin/mingetty tty2
3:2345:respawn:/sbin/mingetty tty3
4:2345:respawn:/sbin/mingetty tty4
5:2345:respawn:/sbin/mingetty tty5
6:2345:respawn:/sbin/mingetty tty6

- Here is the all in one solution..
```
serial --unit=0 --speed=57600
terminal --timeout=5 serial console
title CentOS (2.6.9-55.0.2.EL)
   root (hd1,0)
   kernel /vmlinuz-2.6.9-55.0.2.EL ro root=/dev/VolGroup00/LogVol00 console=tty0 console=ttyS0,57600n8
   initrd /initrd-2.6.9-55.0.2.EL.img
  
```
- Now reboot your server and from another box console in.

Section-2

- First step, follow the First step in Section-1 of this tutorial.

hardware

Add this exec /sbin/getty -L 57600 ttyS0 vt102 to /etc/event.d/ttyS0 (
If this file does not exist please create it) using your favorite editor. (mine is vi

)
This is how mine looks like..

# tty0 - getty
#
# This service maintains a getty on tty1 from the point the system is
# started until it is shut down again.

start on runlevel 2
start on runlevel 3
start on runlevel 4
start on runlevel 5

stop on runlevel 0
stop on runlevel 1
stop on runlevel 6

respawn
exec /sbin/getty -L 57600 ttyS0 vt102

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