Command used to check if a particular software is installed in Ubuntu or not
$ dpkg-query -s firefox
This is the equivalent of “rpm -qa firefox” in RedHat/CentOS
RFC 2616 – Section 3 states:
“Servers should be cautious about depending on URI lengths above 255 bytes because some older client or proxy implementations may not properly support these lengths.”
Different browser agents support different URI length acceptance. In addition, servers too play a role in accepting/denying URI’s over certain length which may either truncate the URI or may give lengthy URI message indications.
It is always advisable to rely on shorter URI’s and to post data when more field sets are to be transferred across web pages.
POST data too has its limit. In this case, it is the size of the data which is controlled by the server settings.
Some interesting discussions:
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
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).
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
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.
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.
By default, ServerSignature is set to Off and ServerTokens is set to Full in most Linux distros.
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
i) ubuntu guide http://ubuntuguide.org/wiki/Ubuntu:Feisty/CDDVDBurning
ii) ubuntu site https://help.ubuntu.com/community/CdDvd/Burning
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
$ cat /etc/hosts
192.168.1.100 myserver.kurinchilion.com myserver
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback