Disk /dev/sdb doesn’t contain a valid partition table in Linux

drive-not-formatted

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1. Run fdisk /dev/sdb

2. Create a new partition table with ‘o’

3. Create a new partition with ‘n’

4. Let it use the default values by hitting ENTER when it asks for numbers, to take the entire available disk in this partition

5. Write the new partition table with ‘w’, which should dump you back to the prompt.

6. Finally, you should have a /dev/sdb1 to format using the following command:

  sudo mkfs.vfat -n ‘Ubuntu’ -I /dev/sdb1

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Http Error 0 in Drupal

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Http Error 0  is a very common error that occurs in Drupal. There are many reasons behind this error.

htttp-error-0

One of the way to resolve this error is to append the following line in this file : /etc/apache2/mods-available/fcgi.conf

[code]

MaxRequestLen 536870912

[/code]

Increase the number value of the MaxRequestLen until the error stops to continue.

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Load Testing on Web Servers using Apache Benchmark

ab

After working on many websites, I found one of my site getting too many traffic bringing down the site. I contacted the technical support who fixed the problem. I had never tested load on any of my site. So, I started studying load testing on web servers. This helped me to understand how many users can be handled by my website so that it can run smoothly.

I found a very light and strong linux tool called Apache Benchmark Tool that can test load on Web Servers. This can benchmark Apache, IIS and other web server with apache benchmarking tool called ab. There are also other open source tools that helps to test load on web servers.

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I executed following command on my linux terminal:

[code]

ab -c 1000 -n 1000 -t 60 -k http://ignou.ac.in

[/code]

Option -c : This option says there are 1000 concurrent users logged in on the Web Server.

Option -n : This option sends 1000 requests to the Web Server.

Option -t : This option says users will be logged in for 60 seconds.

Option -k : For Keep Alive On

I logged in to the web server and executed the following command to test the actual load.

[code]

top

[/code]

This command helped to track down the load average, CPU and Memory Utilization of the web server.

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How to redirect http requests to https on Debian Linux with Apache Web Server?

securing-apache5-590x277

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Do the following to redirect http requests to https running on Debian Linux with Apache Web Server.

File : /etc/apache2/ports.conf

[code]
NameVirtualHost *:80
Listen 80
[/code]

File : /etc/apache2/sites-availabe/default

[code]
<VirtualHost *:80>
ServerName www.example.com
Redirect / https://www.example.com/
</VirtualHost>

<VirtualHost *:443>
ServerName www.example.com
# … SSL configuration goes here
</VirtualHost>
[/code]

Restart Apache Webserver

[code]
/etc/init.d/apache2 restart
[/code]

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Installing and Configuring Commercial SSL on Debian Linux

SSL-Certificate-Secrity-H01CB360EBAB420000000000000004713

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Note: Please note that commercial SSL certificates require a unique IP address for SSL-enabled sites.

a. Enable SSL for Apache and make a directory named “ssl” inside “/etc/apache2/”

[code]
a2enmod ssl
mkdir /etc/apache2/ssl
[/code]

b. Create a Certificate Signing Request

[code]
cd /etc/apache2/ssl
openssl req -new -days 365 -nodes -keyout www.mydomain.com.key -out www.mydomain.com.csr
[/code]

The above command will create a certificate signing request (CSR) for the site which you’d like to use with SSL. Leave the challenge password blank.
Execute the following command to protect the key:

[code]
chmod 400 /etc/apache2/ssl/www.mydomain.com.key
[/code]

Files for your domain will be created in /etc/apache2/ssl. You may now submit the file ending in .csr to a commercial SSL provider for signing. You will receive a signed file after the CA signs the request. Save this file as /etc/apache2/ssl/www.mydomain.com.crt.
Execute the following command to protect the signed certificate:

[code]
chmod 400 /etc/apache2/ssl/www.mydomain.com.crt
[/code]

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c. Get the CA Root Certificate
You’ll need to get the root certificate for the CA that you paid to sign your certificate. You may obtain the root certs for various providers from these sites:
Verisign
Thawte
Globalsign
Comodo
For example, if we downloaded a root cert for Verisign, we would save it to /etc/apache2/ssl/verisign.cer.
d. Configure Apache to use the Signed SSL Certificate.
We’ll add an entry to /etc/apache2/ports.conf for the IP address you’ll be using to host your SSL-enabled site.
File excerpt:/etc/apache2/ports.conf

[code]
NameVirtualHost 12.34.56.78:443
Listen 443
[/code]

Replace the above IP address with your dedicated IP Address. Next, we edit the VirtualHost Configuration file i.e. /etc/apache2/sites-available/default in our case.

[code]
<Virtualhost 10.10.10.109:443>
SSLEngine On SSLCertificateFile /etc/apache2/ssl/www.mydomain.com.crt
SSLCertificateKeyFile /etc/apache2/ssl/www.mydomain.com.key
SSLCACertificateFile /etc/apache2/ssl/verisign.cer

ServerAdmin info@mydomain.com
ServerName www.mydomain.com
DocumentRoot /var/www/
ErrorLog /var/log/apache2/error.log
CustomLog /var/log/apache2/access.log combined
</Vritaulhost>
[/code]

NOTE: You can edit your existing Virtualhost Configuration file (Virtualhost *:80) by adding the above attributes within the Virtualhost tag.

e. Restart Apache:

[code]
/etc/init.d/apache2 restart
[/code]

f. Congratulations, you’ve installed a commercial SSL certificate! You can visit your site with SSL enabled. i.e. https://mydomain.com OR https://localhost/your_website/

[Source: https://library.linode.com/web-servers/apache/ssl-guides/debian-5-lenny]

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Upload Max Filesize PHP Configuration

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I have installed Apache2, PHP5.5 & MySQL5 independently on my Debian 7.3 OS. I hosted my drupal site on my Dedicated Server. I faced problem to upload files greater than 2MB from the CMS of the Site. After exploring the Internet I found the solution. Here’s the steps:

1. Edit /etc/php5/cgi/php.ini file.

2. Add the following line of code:

[php]upload_max_filesize = 10M[/php]

Make sure that you are not editing /etc/php5/php.ini file

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Solution to Url Encoded Slashes (%2F) Problem in Apache

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I was working on Drupal 6. I had to troubleshoot a site that has a problem in its link. The ugly URL looks like this: http://rcportblair.ignou.ac.in/admin/build/employee/search/result/none/0/none/%252F1

The last argument in the link i.e. %252F is a forward slash automatically added by the Drupal engine which was creating problem while generating result. There are many ways to handle these urls. One way is listed below:

<VirtualHost *:80>
    AllowEncodedSlashes On
</VirtualHost>

This directive may be set in server config file (e.g. httpd.conf OR /etc/apache2/sites-available/default) and may appear inside <VirtualHost> containers to affect certain websites. Using it in .htaccess files is not allowed.

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Clean URLs in CodeIgniter and Drupal for Debian based Dedicated Servers

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Initially, when my projects were in CodeIgniter I struggled to find out the solutions for Clean URLs. Now, I am working on Drupal CMS and the process for activating Clean URLs are similar as in CodeIgniter.

drupal&CodeIgniter

1. The first step is to add the following code in your .htaccess file.

<IfModule mod_rewrite.c>
RewriteEngine on

# Rewrite URLs of the form 'x' to the form 'index.php?q=x'.

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ project_dir/index.php?q=$1 [L,QSA]
</IfModule>

2. Next, for Debian Linux OS edit /etc/apache2/sites-available/default file and add the following script.

<Directory "/var/www/project_dir/">
RewriteEngine on
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ project_dir/index.php?q=$1 [L,QSA]
</Directory>

3. If you are using CodeIgniter, the above two steps are done but for Drupal sites, visit the following link from your Drupal CMS Admin: http://your_site/admin/settings/clean-urls. Select the Enabled radio button & click on save.

Congratulations, You have activated Clean URLs for your websites.

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Apache is running a threaded MPM, but your PHP Module is not compiled to be threadsafe. You need to recompile PHP.

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After installing Apache2, MySQL & PHP on Debian wheezy 7.1, I tried to reboot the apache server. It showed me the following error.
Starting web server: apache2[Fri Dec 27 11:29:16 2013] [crit] Apache is running a threaded MPM, but your PHP Module
is not compiled to be threadsafe. You need to recompile PHP.
Pre-configuration failed
Action 'start' failed.
The Apache error log may have more information.
failed!

So I searched through the internet to recomplie the PHP Source. But none of the tutorials were best and feasible.

Finally, after long try I found the command below that helped me to run the apache and PHP along.
apt-get install apache2-mpm-prefork

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Restrict SSH Access by IP Address on Linux

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Here is how to restrict SSH access to certain IP addresses on and off your home LAN.

Edit the /etc/hosts.allow file to include these lines, assuming your home LAN is on the 192.168.4.x nonrouting IP block, and your work address is on the routing 1.1.1.x
IP block: Remember to add the period on the end of each incomplete IP number.
If you have another complete IP address or range, add a space and that range on the end.

# allow ssh login from home LAN and work LAN
sshd,sshdfwd-X11: 192.168.4. 1.1.1.x.

Edit your /etc/hosts.deny file to include this line:
sshd,sshdfwd-X11:ALL
These lines refuse SSH connections from anyone not in the IP address blocks listed.

Log out and then try logging back in to test your configuration. Good luck!

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