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Archive for the ‘Tips, Tricks, Guides’ Category

Aug 16
2009

Premature end of script headers: apache error

Last updated: August 11th, 2009

Apache errors and the approach to solve it

Premature end of script headers
500 Internal Server Error
The specified CGI application misbehaved by not returning a complete set of HTTP headers.

Some troubleshooting tips:

i) Check /var/log/apache2/error.log (in ubuntu, check the respective apache error log location for the messages)

ii) Check if the content type of the page is correctly set for the html content output.

print “Content-type: text/html\n\n”;

iii) Check if a valid permission has been given for the file to get executed. The file need permission 755 for it to be executed on the server.

iv) Check if the configuration path, inclusion path are set correctly in the referenced programs

Aug 15
2009

Permission denied: exec of failed in Apache Server

Last updated: August 11th, 2009

Apache Permission Denied Error can be caused due to one of many configuration mistakes listed below

Check the apache configuration settings

i) The first is the reference to folder where cgi or perl files will reside and its execute permission settings

 <ScriptAlias /cgi-bin/ /usr/local/cgi-bin/>
 <Directory "/usr/local/cgi-bin">
     AllowOverride None
     Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
     Order allow,deny
     Allow from all
 </Directory>

ii) The second is the proper add handlers that are set for the file execution

AddHandler cgi-script .cgi .pl
<Files ~ "\.pl$">
    Options +ExecCGI
</Files>
<Files ~ "\.cgi$">
   Options +ExecCGI
</Files>

Check the apache error log for any messages (/var/log/apache2/error.log).

Aug 14
2009

Ubuntu: Change menu order in GRUB loader

Last updated: August 14th, 2009

GRUB stands for GRand Unified Bootloader. This is to enable the listing of multiple operating systems so the users could choose the OS of their choice.

To change the menu order we need to edit a file called menu.lst

# vi /boot/grub/menu.lst

Look for a line “default 0“. This is the option to indicate that the first menu on the list should be loaded by default. In order for you to set the default menu content in the GRUB loader that needs to get started you can set this parameter.

This is of the form “default <ID>” where ID = N -1. If there are 4 list items in the menu and if you want to load the 4th item by default, you need to set this configuration setting to “default 3″.

Another option for you is to have the menu list with the entry “savedefault = true“. This would enable the last used menu entry to get loaded during the next boot.

Aug 13
2009

Mount, Read, Write, Access USB Flash Drive in Ubuntu

Last updated: August 10th, 2009

How to access USB Flash Drive?

To know the drives and their partition you need to execute
# fdisk -l

Another option is to list the last 5 entries from /dev to know what devices got attached
$ ls -ltr /dev | tail

And another option is to use the lsusb command.

USB Flash drive will normally be listed down as /dev/sdb1
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Aug 12
2009

su vs. sudo

Last updated: August 11th, 2009

The help pages state …

su – run a shell with substitute user and group id’s
sudo – execute a command as another user (or root)

When ‘sudo‘ is used with a command, the command gets executed with privileges set for the user and the group she belongs to. If a password is required and if it is given initially, the session will be valid depending on the time set for each session and the user needn’t have to type the password within that duration. /etc/sudoers is the location where permission settings for sudoers are being set.
(more…)

Aug 08
2009

How to hide Apache version, Modules loaded, PHP Version?

Last updated: August 4th, 2009

It is often advisable not to disclose information than is necessary when web request are made to Apache server.

By default, Apache displays the version of the server, modules loaded in the server and the version of PHP if PHP is configured with Apache.

In httpd.conf file, set the following directives.

ServerSignature Off
ServerTokens ProductOnly

By default, ServerSignature is set to Off and ServerTokens is set to Full in most Linux distros.

Aug 06
2009

How to burn ISO image from Ubuntu Command Line?

Last updated: August 4th, 2009

First list down the CD/DVD devices connected to your machine and find the device name. Some of the tools that comes handy in an Ubuntu machine are ‘wodim’, ‘genisoimage’

Wodim stands for Write Data to Optical Disk Media. If you don’t have the software installed in your Ubuntu release do an apt-get

$ apt-get install wodim

To know more about wodim and its parameter definition try man on wodim

To list the CD/DVD devices on the machine, issue

$ wodim –devices

wodim: Overview of accessible drives (2 found) :
————————————————————————-
0 dev=’/dev/scd0′ rwrw– : ‘HL-DT-ST’ ‘CD-RW GCE-8481B’
1 dev=’/dev/scd1′ rwrw– : ‘HL-DT-ST’ ‘DVD-ROM GDR8161B’

Our read-write CD device is in /dev/scd0. So our command for burning the .iso image

$ wodim dev=/dev/scd0 driveropts=burnfree -v -data ubuntu8desktop.iso

To burn audio files

$ wodim dev=/dev/scd0 driveropts=burnfree -v -audio one.wav two.wav three.wav

Further read
i) ubuntu guide http://ubuntuguide.org/wiki/Ubuntu:Feisty/CDDVDBurning

ii) ubuntu site https://help.ubuntu.com/community/CdDvd/Burning

Aug 04
2009

Ubuntu, Apache: Virtual Hosting

Last updated: August 4th, 2009

Virtual Hosting in Ubuntu Hardy Heron: Case Example

Consider the case of two domain names mysite1 and site2 to be served on IP Address 192.168.1.100 (port 80)

Before proceeding let us look at how resolv.conf and hosts file are set up …

$ cat /etc/resolv.conf
search kurinchilion.com
nameserver 192.168.1.100

$ cat /etc/hosts
127.0.0.1 localhost
192.168.1.100 myserver.kurinchilion.com myserver

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

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Aug 03
2009

Apache, Ubuntu, CentOS: Virtual Host Configuration

Last updated: July 30th, 2009

What is Virtual Hosting?

Virtual Hosting is a technique by which web servers can serve more than one domain name on the same server. It can also be a variation of serving different sites on the same IP but on different ports.
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Aug 02
2009

MediaWiki: The requested URL /index.php/Main_Page was not found on this server

Last updated: July 29th, 2009

Some possible solutions to this problem:

i) Check if .htaccess file is making any redirections

ii) Check if /LocalSettings.php have any invalid reference to root

ii) If you have freshly installed the server, check if AppArmor or SELinux is installed on the machine. If it is try to remove those software and try you website url.

To remove appArmor follow the below steps:

$ /etc/init.d/apparmor stop
$ update-rc.d -f apparmor remove
$ apt-get remove apparmor apparmor-utils


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