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system admin

15
Apr

Whats in your MBR ??

Master Boot Record or the MBR max to 512 Kb but very essential have you ever looked at what your MBR contains most probably NO!!, so try out the following 2 commands as root and check your MBR Contents

# dd if=/dev/hda of=mbr.bin bs=512 count=1
# od -xa mbr.bin

This will display your MBR change hda to sda if u have an sda type disk, following is my MBR you might not understand anything from this but a careful look is required to know what is it :)

0000000 48eb d090 bc66 7c00 0000 c08e d88e e689
k H dle P f < nul | nul nul so @ so X ht f
0000020 bf66 0600 0000 b966 0100 0000 a5f3 23ea
f ? nul ack nul nul f 9 nul soh nul nul s % j #
0000040 0006 8000 80fa 057c fa80 7e87 b202 8880
ack nul nul nul z nul | enq nul z bel ~ stx 2 nul bs
0000060 4916 6607 bebf 0007 3100 66f6 04b9 0203
syn I bel f ? > bel nul nul 1 v f 9 eot etx stx
0000100 00ff 2000 0001 0000 0200 90fa f690 80c2

25
Mar

Restoring GRUB after a reinstall

You had just did a weekly install of some OS which did not detected Linux, Follow the steps mentioned below to get GRUB working again. Please note this would erase the current bootloader and install a new one for you if you are unsure of what you are doing do not try this

  1. Boot from a Linux Live CD ( ex ubuntu or knopix, i use Ubuntu)
  2. Open the terminal
  3. Follow the commands mentioned below
  • sudo grub

if sudo doesnot works switch to root user and use grub drectly, Find the ROOT device you will get the values for X & Y which will be used later.

  • grub> find /boot/grub/stage1

Set the root device from the information achieved from the above command

  • grub> root (hdX,Y)

Install GRUB

  • grub> setup (hd0)

Exit GRUB

20
Mar

User / Group Disk Quotas A three Step Guide

A disk quota is a limit set by a system administrator that restricts certain aspects of file system usage on modern operating systems. "Wikipedia"

Requirements : Quota Package

Where to get it : Quota package is generally available in majority of Linux Distros but still if your distro doesn't provide you with Quota compile it from http://sourceforge.net/projects/linuxquota/ :)

Step 1) Installation :

a) openSUSE : yast -i quota

b) Ubuntu : sudo apt-get install quota

c) Fedora : yum install quota

d) Others : Use rpm or compile if not available

 

Step 2) Enable Disk Quota

Disk quota is generally applied on a user or a set of users to its recommended to enable Disk Quota on your Home partition dont enable quota on the root partition unless you are under the expert category

16
Mar

How to Masquerade (ICS) in Linux

Its very simple to masquerade in linux with few lines of iptables and ip_forward commands.

Assumptions : Your Linux box has 2 NIC's one connected to internet (eth0) other connected to local network (eth1 IP 192.168.0.10)

first of all you have to flush and delete existing firewall rules which are there by default in linux .

so flush rules by typing the following in terminal

iptables -F
iptables -t nat -F
iptables -t mangle -F

now delete the chains by using

iptables -X
iptables -t nat -X
iptables -t mangle -X

now its time to save iptables so type

service iptables save
service iptables restart

now all rules and chains will clear !

check it by /etc/sysconfig/iptables which has all defaults rules set to accept.

now open /etc/rc.d/rc.local

and insert the following line

2
Mar

Skype in Ubuntu

Skype is not available in the default configured repositories of Ubuntu so an alternate is downloading a deb package from skype and installing it but as i am an apt-get fan i would recommend adding the repositories listed below and then using

# sudo apt-get install skype

But you need to Add a Repository using the commands below before using apt-get if there is no command listed for your distro goto Medibuntu

  • Ubuntu 9.04 "Jaunty Jackalope"

wget http://www.medibuntu.org/sources.list.d/jaunty.list --output-document=/etc/apt/sources.list.d/medibuntu.list

  • Ubuntu 8.10 "Intrepid Ibex"

sudo wget http://www.medibuntu.org/sources.list.d/intrepid.list --output-document=/etc/apt/sources.list.d medibuntu.list

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