Recovering or troubleshooting GRUB2 prompt in Debian GNU/Linux

Due to some reason, I was in need to replace existing HDD with new one. So I cloned it using CloneZilla. It was a GNU/Linux Machine. First of all CloneZilla refuses copy partitions, one after another and flagged error for each of one. I remembered the reason for errors and turned off the machine. Turned on again and SHUTDOWN properly. The point is, if Machine is not shutdown properly, file system is unclean and  ColneZilla will complaint while cloning. So I fixed that first. Then cloned without any error. But Computer refuses to boot from newly  cloned HDD. It stayed at grub> prompt

Then I did the following to troubleshoot

Step1. grub> set root=(hd0,1)                                       #  / (root) partition was /dev/sda1

Step2. grub> linux  /vmlinuz root=/dev/sda ro

step 3 grub> initrd /initrd.img

step3. grub>boot

Machines rebooted

on the command prompt as a root

#grub-install  /dev/sda
Rebooted again. Its done.

Reference: https://help.ubuntu.com/community/Grub2/Troubleshooting

Iptables rules to limit time & quota based access

Here are the rules i have add to my GNU/Linux Firewall to limit time and quota for my kids for internet and Xbox live

To limit Quota ( I have just allotted 2GB will increase later on)

iptables -I FORWARD 5  -s 172.16.0.33 -p tcp -m quota –quota 2147483648 -j ACCEPT

iptables -I FORWARD 6  -s 172.16.0.33  -j DROP

For quota ofcourse i have to reset the quota again. I will try to automate it some how

To limit time

iptables -I FORWARD 7 -s 172.16.0.33 -p tcp -m multiport –dport http,https -o eth0 -i eth1     -m time –timestart 16:00 –timestop 18:00 –weekdays Mon,Tue,Wed,Thu,Fri,Sat,Sun -j ACCEPT

Reference:  http://linuxgazette.net/108/odonovan.html

(Above said link had a little typo in time based rule is –days instead of –weekdays

Debian GNU/Linux Nagios3 Bug

I had installed the Nagios3 form package. Installation was fine. I was getting the error message as shown in Screen shot

Even making changes for  ACL’s in Apache conf result noting.

Google is always our friend.The link shown below explained about the bug.

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=626462

I have changed file as shown

Added the index.html in /etc/apache2/conf.d/nagios3.conf. So the line should be

DirectoryIndex index.php  index.html

not

DirectoryIndex index.php

/etc/init.d/apache2 restart

Done!

Have Fun

Ucarp setup for Debian Squeeze

It was easy

Do the following on both  Load Balancers ( I did it on Nginx LBs)

1. apt-get install ucarp

2. vi  /etc/network/interfaces and append the lines starting from ucarp-vid 3

3. replace password and ip (192.168.69.11) with your own

4. Reboot

I have followed the link below. Tested it by shutting down both Load Balancers one by one.

Will dig more in to it. It is Awesome!.

Reference http://forsetti.wordpress.com/2011/09/10/ucarp-and-squeeze/

Have Fun

GNU/Linux Screen Utility

screen command refrence nice link

http://aperiodic.net/screen/quick_reference

Have FUN

Nginx as a Load Balancer

It is very basic setup of Nginx as a  load balancer. I have two Apache servers (web1.meapay.com & web2.meapay.com). Ngnix will act as a load balancer in front of these two servers

I have done it on Debian squeeze. So first we have to install nginx package

#apt-get install nginx

Edit the nginx configuration file. Before editing,  I have copied the original nginx conf file as default.orig

#cd  /etc/nginx/sites-available/

#/etc/nginx/sites-available# cp default default.orig

#vi  /etc/nginx/sites-available/default

upstream mysite {
                server web1.meapay.com;
                server web2.meapay.com;
                }

server {

        server_name  http://www.meapay.com:80;
        #listen   [::]:80 default ipv6only=on; ## listen for ipv6
        access_log  /var/log/nginx/access.log;

        location / {
                proxy_pass http://mysite;
                proxy_set_header   Host $host;
        }

}

#/etc/init.d/nginx restart

Its done.

Have FUN

Reference:

http://mickeyben.com/blog/2009/12/30/using-nginx-as-a-load-balancer/

Mounting RAID array device in /etc/fstab in Debian GNU/Linux

May be helpful for you while mounting RAID array device in /etc/fstab

While making entry in /etc/fstab for newly created RAID device,  we need either device name (/dev/md7) or UUID. I got the UUID using the command

#mdadm –detail /dev/md7

and made the entry in fstab. But it did not worked as per  expectation

Searched Google about the problem as usual. I found that we have to use the UUID provided by the following command

#blkid /dev/md7

not by the command mdadm. Both UUID are different. It works. I have no idea why they are different. So please if you find please tell me as well.

Have FUN! again

Copy GPT Partitioning layout to other hard disk drive

To copy GPT Partition layout to many drives we need sgdisk. sfdisk cant do that.

As of Debian 6.0. Installer does not have sgdisk. So I had rebooted the machine from Gparted live cd. and ran the command given below.

Note that the /dev/sdb is destination drive and source is second device(/dev/sda) (exchange them at your own risk). It will copy partition layout from /dev/sda  to /dev/sdb

#sgdisk -R=/dev/sdb /dev/sda

The command below is required coz the first command copy/assign the same GUID to new device. So to assign another random unique GUID run the following command

#sgdisk -G /dev/sdb

Have FUN!