Shell is an environment around the Kernel providing user interaction. It accepts user commands and convert them to binary code. It is not part of the kernel but uses the kernel to execute the commands. Commonly available shells - BASH (Bourne Again Shell) - CSH (C Shell) - KSH (Korn Shell) All these shells do the same job and the differences come in the form of syntax that these shells use to execute commands and the built-in functions that comes along with it. You can find the shell that is in execution by typing $ echo $SHELL To find all the available shells in the system, type $ cat /etc/shells

To create a password file and to add users to it, use the command $ htpasswd -cm /secured/.mypass username1 To add users to the already existing password file, use the command $ htpasswd -m /secured/.mypass username2 When additional users are added to the password file, ensure that you don't use the "-c" option. Read Password protect directories here

When setting up a workstation to connect to internet, you may come across a message Determining IP information for eth0... failed The above error message basically means that eth0 i.e your network interface card is not setup correctly. Some of the commands that can come handy in troubleshooting where the error lies are listed below $ dmesg | grep eth0 (displays information about the ethernet controller card, mac address etc.) $ cat /etc/sysconfig/network(displays the network settings) NETWORKING=yes HOSTNAME=localhost.localdomain GATEWAY=192.168.122.1 $ cat /etc/sysconfig/network-scripts/ifcfp-eth0 $ ifconfig eth0 down (to down the nic) $ ifconfig eth0 up (to start the nic) $ netstat -rn (display kernel routing IP table) $ cat ifcfg-eth0 (eth0 configuration settings) DEVICE=eth0 BOOTPROTO=dhcp HWADDR=00:16:18:33:B3:CF ONBOOT=yes $ service network restart (restart the network settings) $ ping -c4 google.ca(to check if the internet connection works) $ traceroute google.ca (to check how the IP navigation path is set) Refer Red Hat linux 5 configure network article for additional info

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: Limit on query string GET URL parameters

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