Installing Perl/CGI Scripts

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			What does chmod xxx mean? What is chmod?
	Short Answer Chmod is a Unix command which changes the security settings for particular files, giving users and groups permission to read, write, and/or execute certain files. Long Answer For many of my scripts, the uid (User ID) that the web server is running under must either execute (in the case of the perl scripts) or write or read certain files. There are several different cases in which different chmod commands will be used. For example, any of the perl scripts that must be placed into the cgi bin, must also be executable by the web server. This means you must use chmod 755 filename.pl This allows anyone to read and execute your file and it allows you the permission to write to it. Any of the files that are automatically updated by perl scripts, must be writable and readable by all, including the web server uid. Unless you have super user access, this means setting your files to chmod 777 filename.[html|txt] This will allow everyone to write to your files. If you are still confused on this matter, you must know that to use chmod you must 1) Have a unix account, 2) Be able to ssh/telnet to that unix account or dial up into the account, and; 3) be able to use the shell. If you do not have either of these, you will need to ask your system administrator how you can get around using chmod or what you need to do in order to get it to work.

			What is a cgi-bin?
	Short Answer A cgi-bin is a special directory designated in the config files of a web server to allow execution of CGI scripts in specified directories. Many new servers have done away with this and allow users to execute any scripts ending in .cgi. Long Answer The cgi-bin is used to help keep systems secure. Keeping CGI scripts limited to trusted users is necessary since CGI opens up a lot of security risks. Therefore, most web platforms allow only files inside of a cgi-bin to be executed. This can be changed and on many machines a .cgi extension has been implemented to let anyone use CGI scripts in their directory simply by changing the filenames to have .cgi extension. If this has not been enabled on your system and you don't have a cgi-bin already, ask your system administer if you can have access to execute CGI scripts on your server.

			What is #!/usr/bin/perl and do I need to modify it?
	Short Answer This line must be the first line in your perl program source. It tells the shell that is executing this script where the perl binary is to be used to run this program. Long Answer This line must be in your perl script as the first line to get it to run right. This often causes a 500 Server Error if this is not set as your first line or if it is set in the wrong place.

			What does Server Error 404 "File Not Found" mean?
	Short Answer The URL in one of your scripts that pointed to a file was wrong. The file was not found. Long Answer Make sure that all of the URLS are correct in the scripts and make sure that when the necessary portions of certain URLS are combined they form complete URLS. This isn't one of the most common errors received when setting up my scripts, but many do enter the URLS wrong or do not change them from the standard distribution.

			What does Error 500 "Malformed Header From Script" mean?
	Short Answer Something Went Wrong. Sorry, that's about as specific I can be with a '500' Error. It could be ALMOST ANYTHING. However, you probably are not using a valid cgi-bin or have uploaded the file via FTP in the binary mode in lieu of text. Long Answer Error 500 could be ANYTHING! (almost). Below is a list of some of the most common problems and how you can go about fixing them. Check to make sure that the ACTION="" of your script is pointing to the correct CGI program. If it is, make sure that this file is also chmoded 755 so that everyone, including the Web Server User ID has permission to execute it. Check your server's error_log. On CybrHost servers, this will be located at: /home/sites/site(your site number)/logs/error_log Check the error log right after you receive this error. They will often give you insight as to why you received this error. If there are problems with the scripts, correct any that the error_log may mention. Run the script from the shell and make sure that you don't get any errors. Make sure all files that are supposed to be opened during execution by the script are chmoded so that the web server can read them. Check all paths to certain commands and make sure they are correct. An incorrect path in your script will cause execution of your script to halt. Check your #!/usr/bin/perl line and make sure that it points to the proper location of the perl binary on your system. These are just a few of the MANY possibilities. If you have solved this problem in another way, let me know so I can add it to this list. If you have done all of this including reading the README file and doing what it says to each script, feel free to email me with your problem.