CGI Script Installation Tutorial 9.Start installation now!
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Benny Alexander
December 23, 2004
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Open the
readme file in a text editor and start reading it carefully. Make sure you have
the complete list of files that have to be installed. You can find it in the
list of files from the Help Text file. (Mostly, script developers do this
documentation to help you locate the missing files). If your download was
successfully done without any interruption, you probably have all the files
needed for installation. Let's learn how to use any script file with these 5
easy steps.
1.
Follow the installation document. You will be asked to open
a .cgi or .PL file in a text editor as the first step. In almost any file of
this type, you find the following
This
line must be in your Perl script as the first line to get it to run right. It
often causes a 500 Server Error if this is not set as your first line or if it
is set in the wrong place. Copy the path of Perl program in your server noted
down during the previous lesson as the first line of your program, with' # !' in
the front. Should this command fail, ask your system administrator if they have
Perl installed on their server and to where you should point this line.
2.
Keep reading the .cgi or .PL file, you'll find some lines telling about the
directory path and URL settings of your cgi-bin directory. Change the cgi-bin
path in this file to the one noted down. Follow the other instructions in the
script file given as Remarks. (All the lines which you find that start with #
symbol are remarks or comment statements) Sometimes the author gives you a
warning like "You should not edit anything below this". Its advisable to follow
these warnings. You make any changes violating this warning, at your own risk.
Then, you may be asked to open some more script files to do the same settings as
above. Go one step at a time carefully. It is easily done. Let us pause for a
moment here and learn a little more about the cgi-bin.
The
cgi-bin is a special directory in the server where we keep all the files which
require security. Limiting access of CGI scripts to trusted users is necessary,
since the CGI opens up a lot of security risks. Therefore, most web platforms
only allow files inside of a cgi-bin to be executed. This can be changed. If the
cgi-bin has not been enabled on your server, or if you don't have one, ask your
system administrator to give you the privilege to execute CGI scripts on your
server.
A
cgi-bin is needed to run these scripts unless your system administrator has
turned on ExecCGI, which enables .cgi extensions to be used in any directory. To
find out if you can use CGI scripts, your best bet is to ask your system
administrator if you can. He/She may opt to give you a cgi-bin in your
directory, turn on ExecCGI or check your script and then place it in the server
cgi-bin.
Just
make sure you set all variables to reflect any changes you have to make to the
location of files and scripts by double checking.
3.
Now you are ready to upload. You can upload all the files after completing
all necessary changes There are two modes of uploading, ASCII and Binary. You
can upload the .cgi, PL, .confide, .cfg, .setup and .txt files in ASCII mode,
because basically they are text. Upload any image files like .jpg or .gif in
Binary mode. If you don't follow this you will not be able to execute the
script. If you upload any script files in Binary mode it will crash the script
too. If you find that you have done it accidentally, delete the server file and
upload a fresh copy from your local hard drive, carefully this
time!
4.
Now you would like to change the permissions of the script files but first
you need to know that this is place where people often make mistakes and fail in
installing scripts. You should be clear about chmod(changing mode or
permission), so don't skip this area.
File
permissions allow read, write, and execute access to users based on their user
identification (also known as uid), and their membership to certain groups. You
can use the command: chmod to change a file's permissions. Here is an example:
Chmod
is a UNIX command which changes the security settings for a particular file,
giving users and groups permission to read, write, and/or execute certain files.
For
the script files, you need to make them executable. The code for that is 755.
You only need to do this once. When you FTP the file again, it will overwrite
the old file but the permissions will stay the same. Also note that some FTP
software (like WS_FTP) have a builtin option to let you change the permissions
without having to telnet to the server. Your server however has to support that
feature. If you are interested in setting permissions from your FTP program,
keep reading this section for more information on exactly what the permissions
numbers (755 or 666) mean; or you can jump ahead to step 5, if you are not
curious.
After
you chmod the file, type in ls Ls (that's Ls[space][dash]Ls) and it will
show a directory listing. In WS_FTP you can view it by pressing the Refresh and
DirInfo buttons. Notice that next to the .cgi files, there is something that
looks like:
For
our purposes, we can ignore the first symbol. The "r" symbol stands for read.
The "w" symbols stand for write. And the "x" symbols stand for execute. Now, the
above line of symbols is actually divided into 3 categories. (Ignoring the first
symbol as stated above) the first three symbols define the permissions for the
file's user (probably you). The second set of three symbols define the
permissions for the file's group. (If you and many other employees are working
on a web project together, you might be set up on the server as a group so you
can edit each other's work). The third set defines the permissions for everyone
else ("others" or the "universe"). So by doing chmod 755 filename.cgi, you or
your group can read, write, and execute the file. Everyone including the
Internet browsers, can read and execute the file.
So
what does the number 755 stand for? Notice that this has 3 digits. As you would
expect, those 3 digits correspond to the three different sets of permissions
(file's owner, file's group, and others). Here are what each individual digit
stands for:
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1 = - - x
2 = -
w -
3 = - w x
4 = r - -
5 = r - x
6 = r w -
7 = r w x
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Therefore: 755 = r w x r - x r - x (We don't have to bother about the
leading character). For more about chmod visit here. 5. After you
have the permissions set, jump over to your browser and try to run the
script. Your installation help file will tell you which URL you need to open. It
could be a .cgi, PL or a .html file. Now of course, according to Murphy's Law
there will inevitably be some kind of internal server error. Don't panic. That
just means that something (hopefully minor) is wrong with how the script is set
up. You need to double check once again from the beginning and here is a check
list that can help you.
CGI scripts root directory path and URLs - Make sure its correct
ASCII or Binary ? Which mode did you upload?
Permissions of the script files, directory you created and other text
files.
Location of the files you uploaded.[Script files - Inside cgi-bin.Others
probably outside]
Did you miss any files?
Make changes in all of them?
Finish all the instruction in the list from your installation help file
?
Some scripts are using SSIs.(Egs Poll/Vote scripts).If you run any Server
Side Include(SSI) make sure your server is enabled with this
facility.
After
checking all of the above, when you run the script, did you get something other
than the error message? Good! You are lucky this time and you can start working.
Oh! somebody is saying that they haven't succeeded there. I really want to help
you too.
We can pinpoint the
problem from the type of error messages the browser gives. After submitting the
entry via the form or opening the script file in the browser you may see an
error message. Let us diagnose the problem, correct the script and, next time,
let us stop the browser from screaming.
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