Admins eHow SysAdmin Tips & Tricks

April 17, 2012

How to create a mirror of a site using wget

Filed under: General,linux — Tags: , , , — admin @ 7:33 am

First you need to make sure you have the latest version of wget, some distros are still being released with older versions of wget which has some bugs regarding mirroring functionality. currently the latest version is 1.13.4, so if you don’t have the latest version, you can download and build it from following link :

after building the wget, make sure the latest version is being used :

wget -V

output :

GNU Wget 1.13.4 built on linux-gnu.

+digest +https +ipv6 -iri +large-file +nls -ntlm +opie +ssl/gnutls 

    /usr/local/etc/wgetrc (system)
Locale: /usr/local/share/locale 
Compile: gcc -DHAVE_CONFIG_H -DSYSTEM_WGETRC="/usr/local/etc/wgetrc" 
    -DLOCALEDIR="/usr/local/share/locale" -I. -I../lib -I../lib -O2 
Link: gcc -O2 -Wall -lgnutls -lgcrypt -lgpg-error -lz -lrt ftp-opie.o 
    gnutls.o ../lib/libgnu.a 

Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Originally written by Hrvoje Niksic <>.
Please send bug reports and questions to <>.

OK, you are good to go now, just execute the following command and relax 🙂

wget -mkp -e robots=off http://site

April 11, 2012

My favorite smartphone wallpapers

Filed under: Android,General — Tags: , , , , , — admin @ 6:36 pm

These are my favorite wallpapers on my SGSII, I hope you enjoy them 🙂

You can download them here : SGSII-Wallpapers

March 19, 2012

Simple Timer Utility

Filed under: General — Tags: , , , , — admin @ 6:15 pm

This is another utility which I wrote for myself use, it is a simple countdown timer which beeps when it reaches zero.
You can download it here : Timer

February 26, 2012

How to update Adaptec raid driver on Centos & RHEL5

Filed under: CentOS,General — Tags: , , , , , , , — admin @ 6:51 pm

Download the driver RPMs from adaptec website, as I have 5805z controller, I downloaded the drivers from here :

You will get a file like this :


unpack it :

tar zxvf aacraid_linux_rpms_v1.1.7-28700.tgz

to get :


install rpm :

rpm -ivh --force aacraid-1.1.7-28700.rpm

it will only extract the files to /opt/Adaptec/aacraid :

cd /opt/Adaptec/aacraid
mkdir mods
mv aacraid_prebuilt.tgz mods
cd mods
tar zxvf aacraid_prebuilt.tgz
rm *.tgz

now you have prebuilt module for different kernels, copy the appropriate kernel module to aacraid.ko path, a command like :

cp aacraid-2.6.18-238.el5xen-x86_64 /lib/modules/2.6.18-274.18.1.el5xen/kernel/drivers/scsi/aacraid/aacraid.ko

if you have locate package installed, you can easy find all aacraid.ko files :

locate aacraid.ko | xargs -n1 modinfo | grep vers

when it is complete, reboot the server.

January 11, 2012

Fix nginx 502 Bad Gateway error

Filed under: General — Tags: , , , , — admin @ 11:01 am

Today I was getting “502 Bad Gateway” on a Glype proxy installation , after digging into the problem I found out it is a problem of nginx fastcgi buffers , here is how to fix it :
open /etc/nginx/nginx.conf
add the following lines into http section :

fastcgi_buffers 8 16k;
fastcgi_buffer_size 32k;

you config should look like this :

http {
fastcgi_buffers 8 16k;
fastcgi_buffer_size 32k;

restart nginx and fastcgi.

December 16, 2011

Linux Delete Empty Directories (Folders)

Filed under: CentOS,Debian,General,linux — Tags: , , , , , , — admin @ 6:01 am

As simple as one single command :

find -type d -empty -delete

September 26, 2011

Gateway on a different subnet on Linux

Filed under: Debian,General,linux — Tags: , , , , , — admin @ 7:50 am

Theoretically host IP and gateway should be on the same IP subnet. but there are some situations where host IP and gateway subnet are on different subnets. like my situation today. I was assigned two additional IPs for my server by my Data-center, but IPs were from a different subnet compared to server main IP. these IPs will work if you set them as additional IPs. but I needed them to create two new VPS’s on my server with bridged network interface. in this situation additional IPs should serve as main IP address and there is no gateway on same subnet available.
So here are the assumptions :

a.b.c.d is the host IP
e.f.g.h is the gateway IP
a.b.c.d & e.f.g.h are on different subnets.

by default if you try to set gateway by following command :

route add default gw e.f.g.h

you will get this error :

SIOCADDRT: No such process

the trick is simple , first add a route to default gateway itself and then set the default gateway , like this :

route add e.f.g.h/32 dev eth0
route add default gw e.f.g.h

remember you may need to change eth0 to your device name , it may be eth1 or wlan0 or anything.

How to make these route changes persistent ?

For Debian/Ubuntu :
Add the following lines to /etc/network/interfaces :

post-up route add e.f.g.h/32 dev eth0
post-up route add default gw e.f.g.h

September 19, 2011

Steve Jobs’ 2005 Stanford Commencement Address – Must See

Filed under: Apple,General — Tags: , , — admin @ 8:25 pm

If you read my blog , you will know that I am not a fan of Apple. In fact I fight against its dominance and its policies.but I really admire this man, Steve Jobs. He deserves what he has acquired.
I recommend everyone to listen to this speech very carefully several times and make use of advises of this man. What he says and recommends in life is very true and useful.

Watch here :
Steve Jobs' 2005 Stanford Commencement Address

The text of speech :
‘You’ve got to find what you love,’ Jobs says

September 14, 2011

An analysis of recent security breach to DigiNotar and Man-In-The-Middle attack to Iranian users

Filed under: General,Security — Tags: , , , , , , , — admin @ 9:23 am

As I have received several requests from Iranian readers of my blog, I have done some analysis on recent DigiNotar security breach and MITM attack to Iranian users.
This analysis is based on Fox-IT interim report of breach. You can download the complete report in PDF Format from the following link :

What is MITM attack and how to prevent it ?
MITM stands for Man-In-The-Middle. it simply means someone stands between you and destination and intercepts or modifies your communication. it is quite easy when communication is not encrypted.
SSL protocol is originally invented to address this issue. The idea is that a trusted Authority (CA) authenticates the identity of destination and by using some cryptography protocols your connection to authentic destination becomes encrypted and impossible to intercept or modify.
It has been shown that the cryptography methods like AES or RC4 which are employed to encrypt the data are quite effective and very hard to crack. so the easier solution is to attack the base of trust model, the trusted authorities (CA). In this kind of attacks, hackers break into CA systems and forge valid certificates for themselves so they can impersonate themselves as authentic destinations and intercept the data. this kind of attack is used in both recent incidents, Commodo and DigiNotar.
Although the protocol is almost safe itself, unfortunately many of these CAs are vulnerable themselves making the whole process vulnerable.
The FOX-IT report indicates the DigiNotar systems were using Windows (Which is vulnerable in nature) and passwords has been crackable through brute-force attack. (More on this later)

To understand it better, I have created a diagram of recent MITM attack to Iranian users with the goal of intercepting communications between them and Google. the attackers have been able to gain access to Google accounts of users through this attack :

This diagram is self-explanatory. The attacker in middle impersonates itself as Google and establishes a secure connection to the user which is signed by DigiNotar CA. Although the connection is still secure, but users have a secure connection to the attacker, not real Google. so attacker has access to all information sent by user, including username, passwords, cookies and etc.

September 5, 2011

IPTables packet traverse map

Filed under: CentOS,Debian,General,linux,Security — Tags: , , , , , — admin @ 7:23 am



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